---
source: Everything You Need to Ace Computer Science and Coding in One Big Fat Notebook.pdf
imported: 2026-08-21 23:52
type: book
words:
2026-08-21: 66292
2026-08-25: 66289
COMPUTER
SCIENCE
AND CODING
0101010001
11001010110
01101100011
Copyright © 2020 by Workman Publishing Co., Inc.
By purchasing this workbook, the buyer is permitted to reproduce pages for
classroom use only, but not for commercial resale. Please contact the publisher
for permission to reproduce pages for an entire school or school district. With the
exception of the above, no portion of this book may be reproduced-mechanically,
electronically, or by any other means, including photocopying-without written
permission of the publisher.
Library of Congress Cataloging-in-Publication Data is available.
ISBN 978-1-5235-0277-6
Author: Grant Smith
Illustrator: Chris Pearce
Vetter: Dawn Dupriest
Designer: Abby Dening
Concept by Raquel Jaramillo
Workman books are available at special discounts when purchased in bulk for
premiums and sales promotions, as well as for fund-raising or educational use.
Special editions or book excerpts can also be created to specification.
For details, contact the Special Sales Director at the address below
or send an email to specialmarkets@workman.com.
Workman Publishing Co., Inc.
225 Varick Street
New York, NY 10014-4381
workman.com
WORKMAN, BRAIN QUEST, and BIG FAT NOTE-BOOK are
registered trademarks of Workman Publishing Co., Inc.
Scratch is a project of the Scratch Foundation, in collaboration
with the Lifelong Kindergarten Group at the MIT Media Lab.
It is available for free at https://scratch.mit.edu.
Printed in Thailand
First printing March 2020
10 9 8 7 6 5 4 3 2 1
the
complete middle school study guide
COMPUTER
SCIENCE
AND CODING
WORKMAN PUBLISHING
NEW YORK
EVERYTHING YOU NEED TO ACE
COMPUTER
SCIENCE
AND CODING
HI!
In this notebook you’ll find everything you’ll need to
ace computer science and coding: from understanding
computer systems to reading and writing with programming
languages; from using basic algorithms to writing Boolean
expressions; from working with Scratch and Python to
exploring web development. This is the really important
stuff that you’ll need to understand computer science
and to build a foundation in coding.
You’ll find the notes pretty straightforward, with the
following formatting to keep things organized:
YELLOW
• vocabulary words highlighted in
• definitions set aside in boxes
• important people, places, dates,
and terms written in blue
• doodles, graphics, and charts that
show the big ideas
• main ideas underlined
If you’re having trouble in computer science class or
have an issue with a coding project, this notebook will
help. It hits all the major points of computer science and
walks you through the basics of Scratch, Python, and
web development. It’s also a great study resource!
Whether you want to refresh your memory, reinforce
class instruction, or teach yourself the basics, this
notebook is the way to go.
CONTENTS
COMPUTING SYSTEMS
UNIT 1: 1
1. What Is Computer Science? 2
2. What Is a Computer? 13
3. How Do We Interact with Computers? 29
DATA AND ANALYSIS
UNIT 2: 39
4. Storing Information 40
5. Collecting and Using Information 57
SOFTWARE ENGINEERING
UNIT 3: 67
6. Designing Computer Systems 68
7. Testing 73
COME CHECK OUT
8. Documenting 81 MY GAME SO FAR.
9. Incorporating
Feedback 89
10. Collaborating 97
ALGORITHMS AND
UNIT 4:
PROGRAMMING
109
11. Using Algorithms 110
12. Programming Languages 121
13. Computational Thinking 139
HEY!
UNIVERSAL PROGRAMMING
UNIT 5:
PRINCIPLES
147
I AM A
14. Variables 148
DATA TYPE.
15. Conditional Statements 163
16. Loops 179
17. Events 187
18. Procedures 191
PROGRAMMING
UNIT 6:
WITH SCRATCH
199
19. Getting Started 200
20. Basic Algorithms 223
21. Data and Operators 247
22. Control Blocks and Event Blocks 273
23. Reusing Scripts 299
PROGRAMMING IN PYTHON
UNIT 7: 309
24. Getting Started with Python 310
25. Variables in Python 323
LET'S GET
26. Strings 333 CODING!
27. Numbers as Variables 351
28. Lists and Boolean Expressions 365
29. For Loops 381
30. While Loops and Nested Loops 393
31. Conditional Statements 403
32. Functions 423
WEB DEVELOPMENT
UNIT 8: 443
33. What Is the Internet? 444
34. Cybersecurity 463
35. Creating a Basic Web Page 481
36. HTML Text Elements 497
37. Link Elements 511
38. Styling with CSS 523
39. Styling Individual Elements
with CSS 539
Index 555
Unit
1
TURN
THE
PAGE!
Computing
Systems
1111
1
Chapter
WHAT IS
COMPUTER
SCIENCE?
COMPUTER
A is a device that stores and processes
(changes, moves, or rewrites) information. It can perform
complicated computations and organize and store huge
amounts of information. Computer science is the study of
computers and how computer technology can be used to
COMPUTING
solve problems. It involves studying
SYSTEMS
, programming rules, data and analysis,
networking, the internet,
COMPUTING SYSTEM
and how computers affect
All the basic hardware (the parts
our lives. Computers are
you can see and touch) and
better than humans at software (the programs) that work
together to make a computer run.
storing and sharing tons
12
of information, solving complex calculations quickly, and
learning things. Computer scientists use computers' abilities to
help them develop new technologies that make our lives easier.
Computer technology affects the way we live and think.
It can help us solve our problems and make our lives seem
easier, more fun, and safer.
For example:
* Computers helped navigate
spacecraft to the moon
and Mars.
* Robots help surgeons
perform surgeries with
great precision.
* Computers add realistic
visual and sound effects to
movies and video games.
13
Computer scientists use and create technology to solve
problems. They program computers to both complete tasks
better and faster as well as teach them how to do new
things. Becoming a computer scientist means shifting from
being only a consumer (someone who uses something) to
being a creator.
Computer science is a type of problem solving; it includes the
study of computers, their design, and the way they process
information.
Examples of what computer science IS and IS NOT:
COMPUTER SCIENCE COMPUTER SCIENCE
IS IS NOT
creating a phone app watching videos
(application or program) that on the internet
allows friends to share funny of cats riding
cat videos with each other. tricycles.
programming your own playing your favorite
video game. video game.
14
COMPUTER SCIENCE COMPUTER SCIENCE
IS IS NOT
writing a program that doing your math homework
calculates the answers to on your school’s laptop.
the math problems in your
homework.
writing a program to commenting on the latest
automatically post nice picture your friend posted.
comments on your friends’
pictures.
All the examples in the IS NOT list only use technology, while
the examples in the IS list create new technology.
DON'T JUST
PLAY ON YOUR
PHONE.
PROGRAM IT!
15
THE FIVE CONCEPT AREAS OF
COMPUTER SCIENCE
Computer science can be divided into five concept areas
(main parts) of study:
1. Computing
Systems
Computing systems are the
machines that run programs
and process information. Examples are desktop computers,
laptops, and phones. Many electronic devices are run by
PROGRAMS
and have small built-in computers. For example,
dishwashers, TVs, smart watches, and even some light bulbs.
2. Algorithms and
Programming
PROGRAM
ALGORITHMS A set of instructions
and
(or an algorithm) that
programming involve writing
has been translated into
the programs (code) that tell commands a computer
can understand (code).
computers what to do. Programs
can be very complex-like iTunes,
Safari, Chrome, or Roblox-
ALGORITHM
following many different
A list of steps or instructions
instructions. They can also be
written in human language
simple, like a program that that tells a person how to
complete a task.
only prints out the message
“Hello, World!”
16
Writing a program is sometimes broken up into two steps:
STEP 1: The computer scientist
makes a list of step-by-step
instructions for what she wants
her program to do.
Algorithm
STEP 2: The computer scientist
translates her instructions into
a language (code) the computer
can understand. Now the
algorithm is a program.
Programming
Computers are powerful, but they really aren’t that smart.
They can only do what they're told. Programs give
computers the instructions they need to work.
17
better and more secure ways to share information
across devices.
5. Impacts of Computing
Understanding the impacts of computing involve studying
how computers influence our lives, culture, safety, laws, and
behavior. Just because we can make new technologies doesn’t
always mean we should.
We should ask how these new technologies affect the lives
of others.
For example, what if you made a program that could hack
anyone’s phone and delete all their favorite pictures?
Questions to consider:
What would the effect be on the victims’ lives?
How would your actions affect your friendships?
Are there laws against using such programs?
Would it be wrong to share a program like that even
if we didn’t use it ourselves?
Would this new technology make life better or worse
for others?
19
w
1. What is computer science?
2. Which of these are most likely NOT computing systems?
A. Cell phones
B. Newer TVs
C. Books
D. Electronic readers
3. What is a program, and why do computers need
programs?
4. Computer science is NOT:
A. Studying interesting questions like how to make
deliveries faster using an algorithm
B. Building a computing system as a solution to
a problem
C. Playing computer games
D. Understanding how a new computer technology
could negatively impact people
5. What is a computing system? Provide examples of
computing systems.
20
Computer science is the study of using computers
to solve problems.
2
Chapter
WHAT IS A
COMPUTER?
COMPUTER
A stores, shares, and analyzes huge amounts
of data. It can also perform complex math calculations.
Although a CD (compact disc) can store
information like music, it’s not considered
a computer because the CD itself can’t
change information.
COMPUTERS THROUGH TIME
Thousands of years ago,
people made devices like the
ABACUS
to help them calculate
complex math.
23
In the 1600s, computing became
a profession and the word “computer”
meant “a person who makes
calculations.” Computers (the people)
SLIDE RULE
used a tool called the
to help them calculate.
In 1944, during World War II,
the first electronic computer
was made. THIS IS
A BIG
It was called COMPUTER.
COLOSSUS MARK 1
and was used
by the British
government to
crack secret
German codes.
In 1945, Americans created a faster computer called ENIAC.
ENIAC
Stands for “Electronic Numerical
Integrator and Computer,” which
was the first programmable,
general-purpose computer.
24
Early computers were
THIS IS
massive-they took up A BIG
COMPUTER.
entire rooms! These
computers were used
by large businesses,
governments, or
researchers.
The first mass-produced personal computer, the APPLE II,
was introduced in 1977. Owners could use the computer to run
simple programs or play games.
Today, computers are tiny and everywhere, including phones.
Smartphones are considered computers because:
they run programs (like messaging, photo editing,
and maps).
they store information (like photos, contact information,
and documents).
they perform calculations Smartphones are more
powerful computers than
(with a calculator, with the
the computer used on the
clock/stopwatch, with maps).
rocket that took astronauts
to the moon in 1969.
25
PARTS OF A WHOLE
Computers are made up of two parts:
HARDWARE SOFTWARE
and .
Hardware
Hardware is the physical
parts of a computer, like the
keyboard, mouse, and screen.
An easy way to determine
whether part of a computer
system is hardware is to look: If you
can see it with your eyes, it’s hardware.
Software
Software is the set of programs (instructions) that tell
a computer what to do, like phone applications, editing
programs, and entertainment services. There are all kinds
of software: from games for a gaming system, to the
program that runs your microwave, to the web browser
on your phone. Software is
stored on storage devices
(hardware) like hard
drives, flash drives,
and CDs.
26
An application (app) is a program designed for the
user to perform a task—like take a photo.
All applications are programs, but not all programs are
applications. Some programs are for the computer’s use
only—not the person using the computer.
A CLOSER LOOK AT HARDWARE
Hardware can be separated into different categories:
Input
Input refers to the parts used to send information to a
computer, including a keyboard, mouse, game controller,
and webcam.
A LITTLE
TO THE
LEFT!
27
Storage
Storage refers to the parts that the computer uses to store
USB FLASH DRIVES
information, including hard drives, ,
RAM
CDs, and .
USB (UNIVERSAL SERIAL BUS)
FLASH DRIVE
Also known as a thumb drive or a USB stick;
a portable plug-in device used to store information
RAM (RANDOM ACCESS MEMORY)
A type of computer memory where information can be stored
Processing
The processing parts of the computer run programs,
interpret input, and supply output, including the central
processing unit (CPU) and the graphics processing unit (GPU).
CENTRAL PROCESSING UNIT (CPU)
This is the brain of a computer. It receives input information
and executes commands from other hardware and software.
28
It is made up of the main memory, the control unit, and the
arithmetic logic unit.
GRAPHICS PROCESSING UNIT (GPU)
This part of the computer focuses on graphics. Graphics are
images of all kinds (pictures, animations, videos). The GPU
delivers images, animations, and videos that can be viewed
on the computer’s screen. If you want to get the best picture
quality for your favorite computer game, you’ll need a high-
end GPU to make the graphics look good.
Think of the CPU as a jack-of-all-trades (like a handyman)
and the GPU as the master of a trade (like a plumber). The
CPU is great for completing a variety of everyday tasks well;
the GPU specializes in processing display information quickly.
You wouldn’t want a handyman to replace all the pipes in
your home. Instead, you’d want your plumber to use his or her
special skills to perform that task.
29
Output
Output refers to the parts that the
computer uses to send information to you.
This includes the projector, the monitor,
the printer, speakers, and headphones.
The parts of hardware all work together.
Data (information) comes from the
Is a touch screen an
user (who may be a person or a
input or output part?
computer) and goes through the input
It’s both!
device into processing. Data can then
be placed in storage (saved) or taken
out of storage and then sent to the user.
The process is like digestion: We take in food, process it and
store it, and then pass it out.
INPUT PROCESSING/ OUTPUT
STORAGE
30
A CLOSER LOOK AT SOFTWARE
Application Software (Apps)
Application software (apps) are programs that allow the
user to complete tasks.
“App” is short for “application.”
Word processors, internet browsers, and games are all
examples of application software. Every app in a phone’s
app store is also application software. There’s a wide
variety of application software, and programmers can
specialize in one of the subcategories.
FOR EXAMPLE
* A WEB DEVELOPER is a programmer who makes
application software that runs on websites.
* A MOBILE DEVELOPER is a programmer who writes
application software for mobile devices like phones
and tablets.
* A GAME DEVELOPER is a programmer who develops
application software video games.
31
System Software
System software are the programs that make sure the
individual hardware devices work together and properly
OPERATING SYSTEMS
with other programs. like
Windows on a laptop or iOS (the mobile operating system)
on an iPhone are examples of system software. Operating
systems run in the background; you cannot see what they’re
doing on-screen. The operating system makes it possible to
install games, social media, and other apps on the phone.
Applications cannot work
OPERATING SYSTEMS
without the system software.
Programs that communicate
with hardware, allowing
other programs to run in
the background.
32
Hardware and software are pretty much useless on their
own. Only when they are put together in a complete system
do they become tools.
For example:
| HARDWARE | SOFTWARE | FINAL RESULT |
| -------- | -------- | ------------ |
PHONE TO
| CAMERA | + PHOTO APP | = |
| ------ | ----------- | --- |
TAKE SELFIES
KEYBOARD WORD
PRINTED
| + | PROCESSING | = |
| --- | ----------- | --- |
+
PARTY
| PRINTER | PROGRAM | |
| ------- | ------- | --- |
INVITATION
CAR
STREET = SELF-DRIVING
| + | + | |
| --- | --- | --- |
NAVIGATION
SENSORS CAR
PROGRAM
+
CAMERAS
33
w
1. What is the difference between hardware and
software?
2. What is a computer?
3. How have computers changed over time?
4. What kind of hardware is each of these parts?
Choose from input, output, processing, or storage.
A. TV screen:
B. CPU:
C. Keyboard:
D. Headphones:
E. USB flash drive:
5. How are storage and processing hardware parts
different? Are they both necessary for a computer
to work?
6. What is the difference between the CPU and the GPU?
7. Why was the Apple II significant?
34
Hardware is the physical parts of a computer,
and software is the code or programs that the
computers run.
A CPU is the main brain of a computer and runs most of
the programs, while the GPU mainly processes display
information for your screen.
I
computers
38
3
Chapter
HOW DO WE
INTERACT WITH
COMPUTERS ?
Over time, computers have become easier to use. However,
things can still go wrong. When problems happen, there are
things you can do.
HUMAN-COMPUTER
INTERACTION
USER INTERFACE
The (UI) includes all the parts of a
computing system that you use to operate the computer. For
example, the user interface for playing a video game on a
phone includes the touch screen, speakers/headphones, and
the game’s on-screen menus, buttons, and graphics.
39
GRAPHICAL USER INTERFACE
A (GUI, pronounced
“GOO-ey,” like soft brownies) is a type of user interface
that uses icons and symbols on a
screen instead of just plain text. A
GUI makes it easy for just about
anyone to use a computer. Most user
interfaces are GUIs.
COMMAND-LINE INTERFACE
The (command line, or CLI)
uses only text to operate a computer. This type of interface
is more difficult to use because the user must type in specific
commands, or phrases, for it to work. Although most computer
users will never need to use a command-line interface, it’s a
good thing to learn if you’re a computer scientist.
Human-computer interaction You can try out
(HCI) is the part of computer an example of
human-computer
science that studies and
interaction by finding
improves how the user works the “Accessibility”
with computers. UIs are easy settings on your
computer or phone and
for all people to use, including
turning on the screen
those who are blind or low reader to listen to
vision or are deaf or hard of it read aloud what’s
on the display.
hearing.
40
FOR EXAMPLE,
many phones have built-in screen readers.
This allows users who are blind or have a hard time seeing
to still use their phone.
A program that reads aloud
the words on the screen.
TROUBLESHOOTING
Troubleshooting is taking a systematic, or
step-by-step, approach to solving errors
within a computing system or software.
Or, debugging programs in software.
Using a systematic approach means following a fixed
plan or process, step-by-step. Like instructions for making
a PB&J sandwich. If your computer won’t turn on, one
of the first things you would do is make sure it is plugged
into a power source, and then you would check that all the
power connectors inside the
computer are connected WHERE'S
THE
securely. The benefit to a JELLY?
systematic approach is that
you can repeat the steps
exactly and you can be sure
you haven’t left anything out.
41
Debugging is finding and correcting “bugs,” or
errors, within a program. Debugging is a
specific form of troubleshooting that
is used when programming. Bugs
may be caused by typos
or by not following the
rules or format of the
programming language.
Troubleshooting Strategies
Troubleshooters use some of these strategies to help them
find and fix problems:
Swapping in working parts from
other computers, such as monitors,
keyboards, and even hard drives,
motherboards, or power supplies.
Creating a diagram to trace the problem. For example,
creating a diagram of all the components in a computer
system and how they connect to each other helps
a troubleshooter stay organized as they hunt for
the problem.
42
Making changes in the software to see if the hardware
will work. Sometimes a software update has bugs in it
and you may need to go back to the previous version. Or
maybe you just need to install a new driver (a program
that tells the computer how to interact with a piece
of hardware).
Checking software settings and the compatibility
of components. Some software is made for specific
hardware. For example, you can’t install an iPhone app
on an Android phone.
Getting help from a more knowledgeable troubleshooter.
Sometimes an issue is too big for one person to solve on
their own. There are many websites dedicated to helping
people troubleshoot all sorts of computer issues-they
are a great resource to search through.
43
w
1. What is troubleshooting?
2. Which of these is NOT a troubleshooting technique:
A. Using a checklist
B. Getting help from someone else
C. Replacing a computer
D. Swapping out parts one at a time
3. What does taking a systematic approach mean?
Why is it useful?
4. If your computer won’t turn on, which of these things
should you do first?
A. Try to take it apart.
B. Make sure the power cable is plugged in.
C. Assume it’s broken and return it to the store.
D. Press hard on the keys.
5. What is debugging?
6. How is troubleshooting different from debugging?
44
Solving problems by using a systematic, or
step-by-step, approach.
Graphical user interface (GUI)
48
Unit
2
DATA
RULES!
Data and
Analysis
3399
4
Chapter
STORING
INFORMATION
THE INFORMATION AGE
Our world has moved through the Stone Age, the Dark Ages,
and the Industrial Age. Many say that right now we are living
in the INFORMATION AGE. That’s because we have shifted
STONE AGE DARK AGES
PAST
40
from a focus on making stuff with our hands to using
information technology to create. We have found new
ways to use information to help us create.
INFORMATION PROCESSORS
Computers are . This
means they take information and make it easier for us to
use. For example:
Map apps process information from satellites to
help us find the quickest route to our destination
and even avoid traffic.
Social media apps (such as Snapchat, Twitter,
Instagram, or Facebook) process our personal
information (likes, posts, etc.) and create profiles
INDUSTRIAL AGE INFORMATION AGE
FUTURE
41
of who we are that businesses can use to try to
sell us stuff.
Note: You don’t pay anything to use social networks,
but that doesn’t mean they are free: The cost of using
them is that you hand over tons of information about
yourself. That’s why it’s always important to get
guardians’ permission and guidance before giving out
ANY personal information online.
Self-driving cars gather RADAR
Stands for “radio detection
and analyze large amounts
and ranging”
of information to make
predictions and decisions.
RADAR
(using radio
frequency to detect the LIDAR
Stands for “light detection
presence of or distance
and ranging”
LIDAR
from an object),
(using laser light to
measure the distance to a target), ultrasonic sound waves,
and video recordings from cars’ external cameras and
sensors are collected, temporarily stored on the cars’ hard
drives, then sent over the internet to powerful computers
that analyze the data using artificial intelligence (AI)
programs. The AI programs piece the data together to
learn how to drive by analyzing how humans drive safely.
42
ARE YOU WORRIED
ABOUT ROBOTS HOW DO YOU KNOW
TAKING OVER IT HASN’T HAPPENED
THE WORLD? ALREADY?
The more information we have and the better tools we have to
understand the information, the better decisions we can make.
For example, when you try to buy a birthday present for your
friend, it is much easier to do than trying to buy a present
for a new kid that just moved into town. This is because you
have more information about your friend, so you’re able to
make a better decision about what they would like.
COMPUTERS USE DATA
DATA
is a collection of unorganized figures, words, and
numbers that have not yet been given meaning. Data has
many different forms depending on what kind of information
it represents.
INFORMATION
is data that has been organized to have
meaning. A context is given to the data. For example, all
43
the answers to a survey are data, and the average of the
results is information.
Input data is the unorganized information entered into
the computer.
Output data is the information after the computer
processes
the computer has processed it.
INPUT DATA OUTPUT DATA
In a video game: pressing The character moving
keys or buttons on a game around the screen
console
In social media: typing Edited videos and photos
comments or uploading along with your profile
photos and videos
44
INPUT DATA OUTPUT DATA
On a microwave oven: The food cooking in the oven
selecting numbers or for a given amount of time
buttons on the keypad
In a graphing program: A graph of the numbers
entering numbers for
D UGHNUT SALES
different categories
$800
$600
$400
$200
M O N D A T Y U E SD A W Y ED N T ES H D U A R SD F A R I Y D A Y SA T U R D S A U Y N D A Y
Y
Computers take input data like answers to questions,
numbers, and uploaded images and turn the data into a
format they can understand and process. For example,
pictures are broken up into millions of tiny chunks by a
computer, and then the color of each chunk is recorded
45
in a long sequence of
CODE
code. The computer then A system of symbols, letters,
and numbers used to
processes the code and
represent something else
sends it back to the user as
output data. To show the
picture, the computer reads
the long sequence of code and reconstructs the image on
your screen by displaying the corresponding color in each
tiny chunk, kind of like a super-detailed paint by number.
PROCESSING
INPUT OUTPUT
STORAGE
46
ENCODING DATA
Data has to be written in
MORSE CODE
a format the computer will
Uses dashes and dots
understand. This means you to represent the letters
ENCODE of the alphabet
have to the data
so that the computer can
process it. When you encode information, you change an
image, video, words, etc. into code. For example, MORSE
CODE OPERATORS in World War II would encode written
messages into dashes and dots that were sent over
telegraph wires.
An outdated communication system
that used electrical signals.
DECODE
When you information, you
convert code into an understandable
form of communication. For example,
when the Morse code operators would
receive coded messages in the form of
dots and dashes, they would decode
Morse code operator
the dots and dashes back into English.
DATA ENCODING SCHEMES
There are several we
can use to help a computer understand input data. Data
encoding schemes are ways that we can represent all
types of information so that computers can understand it.
Computers only understand sequences of the digits 1 and 0.
47
BINARY
Any code that uses 1s and 0s is referred to as a
CODE
. (This will be discussed in detail later.) Encoding
schemes were created to help computers understand,
interpret, and create data by reducing all data-images,
sounds, videos, numbers, colors, symbols, and other types
of information-to 1s and 0s.
You could imitate the way computers store an image by
making lists of 1s and 0s, where 0 is a white box on the
grid and 1 is a green box. Here’s how the data would be
represented to draw a simple giraffe on a 5 x 5 grid.
ROW 1: 1, 1, 0, 0, 0
ROW 2: 0, 1, 0, 0, 0
ROW 3: 0, 1, 0, 0, 0
ROW 4: 0, 1, 1, 1, 0
ROW 5: 0, 1, 0, 1, 0
Encoding Colors
Different types of data, like colors, numbers, and pictures,
can be encoded in different ways. The most common ways
RGB
colors can be encoded are through the coding schemes
HEXADECIMAL
and .
You can use a scanner to encode an old photograph into digital
data that a computer can understand. Scanners work by
using a sensor that detects colors and encodes the entire
48
photo into a series of number values. The scanner puts all
these values in an order that a computer can understand
and use to re-create the image on a computer screen.
RGB is color notation that uses three numbers separated by
commas, where each number is between 0 and 255 (computers
encode each value to binary numbers). Each of the three
numbers represents a different shade of red, green, and
blue. (That’s where the name RGB comes from!) When the
different shades of red, green, and blue are combined, they
can make many more colors.
There are 16 million ways
to combine three numbers
between 0 and 255. This
means that there are
16 million colors that can
(255, 203, 5)
be represented in the RGB
R G B
encoding scheme.
The hexadecimal color notation (or “hex” for short) uses
six characters to represent the same 16 million colors as
RGB. Hexadecimal is different from RGB because it uses
numbers and letters. It uses combinations of the numbers
0-9 and letters A-F. For example, would make
a pink color by using the letters F and B as well as the
numbers 0 and 4. Each set of two characters (such as
49
FF, 00, and B4) represents a different color: The first two
characters represent red, the next two green, and the
final two blue-and just like with RGB, the different
number/letter combinations represent different shades
of each individual color.
The computer language CSS
uses this symbol to represent
RED GREEN BLUE
hexadecimal colors.
Although data such as colors can be represented in different
ways, the important part is that each color uses an encoding
scheme so that computers can understand the information.
50
Representing Colors
In the table below, the first two columns are schemes
(ways) that computers read colors. Each encoding scheme
is translated into binary code. The other three columns are
examples of how humans read or identify colors.
| COMPUTERS | | | HUMANS | |
| --------- | --------- | ------- | -------- | -------- |
| HEX CODE | RGB | ENGLISH | SPANISH | VISUALLY |
| FF0000 | 255,0,0 | Red | Rojo | |
| 0000FF | 0,0,255 | Blue | Azul | |
| FFFF00 | 255,255,0 | Yellow | Amarillo | |
| 008000 | 0,128,0 | Green | Verde | |
| 000000 | 0,0,0 | Black | Negro | |
Encoding colors into numbers and letters is just one way
information is made readable by computers. Sounds,
keyboard inputs, touch screen taps, thumbprint readings,
GPS locations, and all sorts of data are collected and
encoded into a format that computers can understand.
51
w
For questions 1-3, complete the sentences.
1. We are currently living in the Age.
2. Converting data into code is called .
3. Converting data from code to a readable format is
called .
4. What is the difference between data and information?
5. Label each option below as an example of encoding or
decoding.
A. Green → 008000
B. 000000 → Black
C. Amarillo → 255,255,0
D. FF0000 →
6. How many different colors can be made using
hexadecimal or RGB?
52
Label which color each of these pairs represents in this
hexadecimal code:
→ → →
Information
Red Green Blue
→
→ →
Every post, picture, video, or other bit of information you
share online gives businesses clues about you and what
you like to buy. Companies can sell this information to
advertisers.
RED
FF0000
56
5
Chapter
COLLECTING
AND USING
INFORMATION
There are many ways to collect information. You can:
conduct interviews
hand out surveys
make observations
Computers can be used to make all
EFFICIENT
EFFICIENT
these methods more .
Takes less time or effort
A survey can also be a type of
sensor that takes human input.
Computers can collect and analyze data
faster and more accurately than humans.
57
INTERVIEWS
INTERVIEWS
gather information through asking questions.
They are a great way to gather detailed information from
people. When interviewing, we can ask follow-up questions to
get more information and to more clearly understand the
interviewee. Interviews work great if you only need to collect
data from a small group of people.
The person being interviewed
A downside to interviews is that data from responses is
COMPUTABLE
not easily . This means that we can’t use
a math formula or computer algorithm to find a pattern in
the data. For example, we can’t find the average of a page
of written answers. But we can find the average of a group
of numbers.
SURVEYS
SURVEY
A is a list of questions. Surveys can be completed
and sent digitally through email, websites, or other types
of programs. They can also be completed on paper. The
responses to a survey can give us general information about
a large group of people.
Computers use the information provided in surveys to
efficiently compare large amounts of data.
58
Surveys are great because we can send them out and
people can complete them on their own. Surveys are used
because they save time.
A downside to surveys is that people may not take the survey
seriously, or they may not complete it at all. Another downside
is that it’s more difficult to gather very detailed information
because follow-up questions can’t be personalized.
Different types of survey questions provide different
types of data:
Open-ended questions allow for more detailed responses,
but like interview responses, the data is more difficult for
a computer to analyze.
Multiple-choice questions are great for finding trends and
patterns. Election ballots use multiple-choice questions, where
voters select one candidate for each position. This makes it
easy for a computer to analyze: The candidate with the most
votes wins! The downside to multiple-choice questions is that
the options are limited to the choices given, which means we
won’t get detailed responses like with open-ended questions.
59
LINEAR SCALE QUESTIONS
allow users to rank their
answer. For example, ice-cream taste testers rate how much
they like a new flavor on a scale of 1 to 5, where 1 means
they don’t like it and 5 means they love it.
Computers use multiple-choice questions and linear scale
questions to more efficiently compare data. Computers can
also use the data provided to calculate and identify trends.
OBSERVATIONS
OBSERVATIONS
require looking at an event and making
a record of it.
Data is collected at sports games
through observation. Points, THIS ISN’T THE TIME
TO DO AN INTERVIEW—
fouls, penalties, times, and JUST OBSERVE
HEY, ALL-STAR!
THE GAME!
distances are recorded WHAT‘S THE
SCORE?
to understand much more
than just who won.
Computers can make
comparisons and
predictions based
on observations.
60
USING DATA
The first computing machines were made to calculate
CENSUS
information. The population in the United States
was getting so big that the government needed a way to
add up all the survey data. The
CENSUS
HOLLERITH TABULATING MACHINE
An official count or
was used to calculate the survey
survey that collects
results, which provided useful information about a
population (for example,
information to the government.
where they live, their age,
Computers have always been
and number of people
used to help make sense of large in the household)
amounts of data.
1890—Hollerith Tabulating Machine
A major step toward modern-day computers,
this machine read and summarized
information stored on punch cards.
Charts and Graphs
Charts and graphs are ways to visualize data. Computer
applications use different types of charts to represent
different types of information clearly. Charts and
graphs are tools that data scientists can use to visualize
information in order to analyze it, draw conclusions, and
communicate the information.
61
PLAYER
STNIOP
ANN MAX INDRA CAM MEL
)SDNASUOHT(
SELAS
Line graphs are used to show how something changes
over time. For example, a company could use a line graph
to show the growth in sales of their ebooks.
EBOOK SALES
50
40
30
20
10
2014 2016 2018 2020
YEAR
Bar graphs are used to compare different values in a
category. For example, they can be used to compare the
number of points scored by each player on a volleyball
team.
VOLLEYBALL, GAME 6
6
5
4
3
2
1
62
Pie charts are used to show the percentage of parts of a
whole. For example, they can be used to show the popularity
of different doughnuts sold in a bakery.
DOUGHNUT SALES
PLAIN
JELLY
CHOCOLATE
GLAZED
63
w
1. Which of the following questions would result in easily
computable data? (Choose all that apply.)
A. Do you like eating spicy food?
B. Does your nose run when you eat really spicy food?
C. Draw a picture of the spiciest thing you have eaten.
D. On a scale of 1 to 5, how spicy are the cafeteria’s
jalapeño poppers?
2. Two ways (of many) to collect data are .
3. What is one advantage conducting interviews has over
handing out surveys?
4. If you wanted to find out which sports team is the
most popular among 100 nearby kids, what kind of
data collection tool would you use?
5. If you want to gather easily computable data, which
two question types should you avoid?
6. Give one example of when computers are used to
collect data.
64
A , B , D
Unit
3
READ ANYTHING
GOOD LATELY?
TXT
Software
Engineering
6677
6
Chapter
DESIGNING
COMPUTER
SYSTEMS
THE ENGINEERING
DESIGN PROCESS
When designing computers or programs, computer scientists
ENGINEERING DESIGN PROCESS
follow an to help them
understand and improve their designs. Their goal is to make
the program as efficient and user-friendly as possible.
ENGINEERING
is a branch of science
that studies the design, building, and use
of machines and structures to solve
problems. Computer engineering is the
application of study of computer science
and the practice of engineering to
68
There are many slightly different engineering design processes,
but a basic version is
1. identify the problem
2. plan a solution
3. build/make the plan
4. test
5. improve
and then the cycle
starts again.
computer software and hardware. Software engineering is
an application of computer science.
Step 1: Identify the Problem
Software engineers identify the problem and what they
need to find a solution. They ask themselves:
What is the problem I want to solve?
• Example: find the
shortest way home
from school that includes
stopping at the library
and grocery store.
69
What can be used to help solve the problem?
• a map showing the locations
• distances between locations
• type of transportation used
What features will I need to solve the problem?
• be able to calculate
• be able to draw a map
This stage may include collecting and analyzing data
from people who face the same problem. This could include
interviewing people, sending out surveys, or observing people.
It can also include the use of sensors or GPS tracking.
Step 2: Plan
Software engineers develop plans
for a solution to the problem.
Planning can include
making lists or drawing maps
of a proposed solution. Plans
should be very detailed.
70
Step 3: Build
The code is written, and other parts of the solution are
added to the program. The build step ends when a working
product is completed.
Step 4: Test
Identify problems by testing the source code or solution.
Software engineers usually ask people to use the product
and give feedback. There are
different levels of testing.
In the early stages, the
programmer will run tests on
their own; then they will ask
peers to test their solution.
Later the programmer will ask
a group of users to test the
solution and give feedback.
Step 5: Improve
Fix problems and improve the solution. In this step, the bugs
or other issues identified in the test step are corrected.
71
EVERYDAY ENGINEERING
Powerful technologies have become smaller, cheaper, and
easier to work with, which means anyone can design and
build amazing things. With Lego robotics, drones, 3-D
printers, desktop laser cutters, micro:bits, Arduinos, and
Makey Makeys, you can become an everyday engineer.
micro:bits and Arduinos are very small computers on
a single chip that can be programmed to do a number
of different things, such as keep track of data like a
fitness tracker, or behave like a game controller. They
are used to teach students coding and programming.
Makey Makeys (a type of microcontroller like a
micro:bit or Arduino) are electronic invention kits for
kids that allow the user to use alligator clips to connect
everyday objects to computer programs. This allows
the user to control the objects in a different way.
72
7
Chapter
TESTING
Testing is an important part of the engineering process. As
Step 4 in the engineering design process, this task takes up
the most time.
Many things can go wrong with programs. These are ways
programmers try to limit the number of problems in their
programs so that they run smoothly.
DEFENSIVE PROGRAMMING
DEFENSIVE PROGRAMMING
is designing your program
so that it keeps working even when things don’t go as
expected. One way to do this is to intentionally get your
program to produce errors to see how you should solve them.
For example, if you write a program where the user should
input their email address, you could try to produce an error
by entering text that is not an email address.
73
Then ask:
Does the program still run correctly if a user inputs their
phone number or name in the email address field?
What can you do to prevent the user from inputting the
wrong information?
IF IT AIN'T BROKE . . . I DON'T
BREAK IT! THINK
THAT'S HOW
IT GOES!
USE CASES TEST CASES
and are used in defensive
programming to help you see where adjustments may be
needed in a program.
Use Cases
Use cases are lists of actions users can take. It describes
how users will use your program.
74
The list could be a very detailed flowchart, or it could be
a few ideas you come up with.
It’s important that the user is able to run a program without
errors. For example, after you complete the programming of
a game, you should play the game from beginning to end to
make sure it runs the way you want it to.
Test Cases
Use case tests check to see if the user can complete a goal
in the program. For every use case, there will be many more
test cases. Test cases are specific, more detailed tests. They
use conditions that your program may run under. The use
case is used to define the functionality required. Use case
testing is then testing for that functionality.
Test cases focus on one condition (or variable) at a time to
make sure the program works in all situations.
For example, if you were creating a video game, you could
create a test case that makes sure your character jumps
when you press the spacebar.
Programming defensively
would mean making sure
If that test passes, you should that, no matter how long
the user held down the
also test to see what happens
spacebar, the character
if you hold down the spacebar
would jump just once.
instead of pressing it just once.
75
If you defensively programmed your game, then the
character will just jump once.
I CAN
If you didn’t defensively program, FLY!
or forgot to test what happens
when the user holds down the
spacebar, the character might
do something you don’t want
them to do.
Another example: If you programmed a calculator app
that divides your number by 10, test cases make sure your
program works with different types of numbers. Would the
program crash if the user tries to enter 1 or 0?
It is important to pick test cases that use many types of
input. For example, for a calculator app, instead of testing
only with digits 0-9, choose positive and negative integers,
rational numbers, and zero.
76
Remember from Math Class
Positive integer: a whole number greater than zero,
not a fraction or a decimal.
For example, 2, 5, 9, 50.
Negative integer: a whole number less than zero,
not a fraction or a decimal.
For example, −1, −5, −150.
Rational number: any number that can be written as
a fraction or a ratio.
−5
For example −5 can be written as — a nd
1
2.15 can be written as 215 .
—
100
77
w
1. Explain the difference between a use case and
a test case.
2. NASA is testing a program by seeing if an astronaut can
use the program to successfully complete all the steps of
a mission from rocket launch to orbiting Earth. Is this
a use case test or a test case?
3. NASA is testing a small part of the launch program-
the part that controls the engines-to see if the program
runs correctly even with different inputs. Is this
a use case test or a test case?
4. You are a defensive programmer if:
A. You think testing is a waste of time
B. Your program will run even if things go wrong
C. Your program protects against a virus
D. All of the above
78
Use cases are the broad tests that determine if a
user is able to complete a general task, while test
cases are specific tests that use various types of input.
8
Chapter
DOCUMENTING
DOCUMENTATION
is information about a program‘s code.
There are two main types of documentation: comments and
README files.
COMMENTS
All programming languages have a way to add comments to
the code. Comments are not part of the program; they are
skipped when the program is run and can’t be seen by the
user. Comments are messages written by the programmer
about the program’s code. They can be explanations about
what a chunk of code does, reminders about things to add
or change in the code, or questions to other programmers
who will look at the code.
Example:
Add a countdown clock at the top of the screen.
81
Commenting on code helps you remember what each section
does. This is helpful for large programs because you won’t
remember what every line of code was written to do.
Comments also are helpful for short programs because you
might want to look at the code long after you finish writing it.
Sometimes you’ll want to reuse code from another program,
or code you or someone else wrote. Comments help you quickly
find the portion of code you want to reuse. For example, if you
were making a game, instead of creating the code to move
characters around on your own, you could copy a similar chunk
of code from another program. You could write a comment so
that you know which chunk of code this is in your program.
Comments are also used to
COMMENTING
help debug a program. Because
OUT
comments are not read when the
Marking sections
COMMENTING
program is run, of code as a comment
OUT a section of code is an easy so that it will not be run
with the rest of the code
way to make the computer skip
lines of code (that may contain a
bug) without deleting them.
Comments can also be helpful in debugging by adding test
lines of code that you comment out when you are done
testing it.
82
Comments can also be notes to yourself as you code.
For example, you could leave short notes as reminders to
yourself like:
back to.
note about what code you still need to write but
need to come back to later.
README
PLEASE
A README file (usually typed in READ ME.
all caps to get your attention)
gives information about a program,
including which files are included, TXT
how to install it, how to use it, credits
and attribution, or known bugs.
A README file can be
PLAIN TEXT FILE
written for the user, other
A text document that
programmers, or both. Usually has no formatting
(like bold type, indents,
only one README file is used
and paragraph spacing);
per program, and it usually is
just words and punctuation
PLAIN TEXT FILE
a .
83
Although README files can include user information, a user
guide is a more common way to help users figure out how
to use a program. Usually user guides are only created for
large, complicated programs like Microsoft Word or Excel.
FASCINATING . . .
READ TXT
ME
84
READING A SMART
=
USER GUIDE IDEA
85
w
1. What are two types of documentation you can make to
help others understand your program?
2. Which type of documentation helps you remember what
small chunks of code are supposed to do?
3. Why is commenting out a line of code helpful in
debugging?
4. Why are comments useful to you and other
programmers?
5. Which of these are reasons to use documentation?
(Choose all that apply.)
A. Makes it easier to find sections of code you want
B. Makes it easier to collaborate
C. You can write notes to yourself while programming
D. Helps you find bugs
E. Gives credit
F. Explains how to use a program
86
Comments and README files
9
Chapter
INCORPORATING
FEEDBACK
USER-CENTERED DESIGN
Users decide whether or not a program is good. Their
opinions will be based on how easy the program is to use
and whether it does what it’s supposed to do.
USER-CENTERED DESIGN
is a process for creating
a program that considers users’ wants and needs at every
stage of development. To make a program work easily for
as many users as possible, you should ask different kinds
of users for their opinion on your program.
Incorporating feedback means using the information
you gathered from users to revise your design.
89
When creating a user-centered design, you should focus on
several things:
MARGARET, I CAN'T GET
USABILITY - CAN YOU COME THE VIDEOS TO
HELP ME WITH COME BACK
Is it easy to THIS NEW
SNAPPING APP?
figure out
NEWB!
and use?
ACCESSIBILITY
-Can people
COOKIES
with different abilities use it?
CONTENT
-Does your
program make sense to the
target audience?
people for whom the
program is designed
90
COLLECTING
SERIOUSLY,
FEEDBACK MORE TESTING?
Before sharing a program
with the world, programmers
ALPHA BETA
use and
testing to get feedback from
users. These users point out
bugs or issues in the program.
Alpha testing is the first round
of user testing, which is usually Alpha (a) and beta (b)
done just before the program is are the first
two letters of the
finished. Alpha testers are
Greek alphabet.
friends or people you trust.
At this point your code isn’t
finished, so you should
expect them to find
COME CHECK OUT MY
plenty of bugs.
GAME SO FAR.
In a coding class,
alpha testing can mean
asking a classmate to
come over and check
your program, even if
it’s only halfway done.
91
Beta testing is the second round of user testing, which is
usually done after the program is finished. Beta testers
are a selected group of potential users.
FOR EXAMPLE,
if you made a new app to help your
friends study for an upcoming math final, the beta testers
would be a group of your classmates in math class. Beta
testers should find fewer bugs than alpha testers.
Showing your program
HEY, MRS. ALVAREZ,
to potential users helps COULD YOU BETA TEST
MY ESSAY BEFORE
to identify flaws you I TURN IT IN?
might have overlooked
before. Fixing these
flaws before sharing
your program with
everyone can help you
catch mistakes before
the program goes out
into the world.
92
w
1. What is user-centered design?
2. Which of the following is NOT a principle of
user-centered design?
A. Entertainment
B. Usability
C. Accessibility
D. Content
3. What is feedback?
4. How is alpha testing different from beta testing?
5. Will an alpha or a beta tester be likely to find more bugs?
6. What does it mean if a program is accessible, and why
does making accessible programs matter?
More questions 93
User-centered design is creating a program
based on what users want.
B
10
Chapter
COLLABORATING
WORKING ON A TEAM
Collaborating, or working with others, on programming
projects is helpful because different people have different
strengths. Having several people work together on a large
program (instructions that tell a computer what to do) can
help the project finish faster. It can also reduce the burden
on the programmer.
STILL
TYPING.
The Space Shuttle
ran on 400,000 lines
of code. New high-
end cars run on
100 million lines of
code. Facebook is
made up of around
60 million lines of code. To write millions of lines of code
by yourself would take more than a lifetime.
97
Collaborating on a project by dividing up the work and
focusing on your strengths will help you build more efficient
programs more quickly.
Tips to help members of a team work well together:
Set clear expectations. Make sure everyone
knows exactly what they are supposed to do
to contribute to the project. Don’t leave out
any parts of the project.
Focus on your strengths. Divide up tasks
so that each person is assigned a task that
they will enjoy doing and will most likely be
good at.
Set realistic timelines. Give yourselves time to
complete the work, but also push yourselves
to work hard and finish the project.
98
Give equal workloads. Although each team
member will be doing different tasks, make sure
the work is divided equally so no one feels that
they are stuck doing all the work.
Create clear roles. Decide who should be the note
taker, the tester, the debugger, or any other role
you might need. Clear roles will help you keep on
track and focus on your own tasks.
DESIGN CODE ARTWORK
FOR THE APP FOR THE APP FOR THE APP
99
PAIR PROGRAMMING
When projects are really small, like those you might do
in a class, programming with a large team may be too
PAIR PROGRAMMING
much. is a strategy where two
people work at the same computer to complete a project.
Programmers use this strategy because it helps them
work faster and make fewer errors.
In pair programming, each coder has a specific role. One
DRIVER NAVIGATOR
person is the , and the other is the .
The driver is in control of the keyboard. They are in charge
of typing in the code and
NAVIGATOR DRIVER
double-checking their
work. The navigator
is in charge of telling
the driver what
code should be
written and for
catching bugs
while working.
Both the driver and the navigator should communicate
with each other while coding. Pairs should rotate roles
often so that each person has a chance to drive and
navigate.
100
GETTING HELP FROM
THE COMMUNITY
Most programmers spend a lot of their time searching
for solutions to their programming problems. When you’re
making a program you can use many resources to help you
finish the project. Even experienced programmers ask other
programmers for help.
When you’re programming, you should look for opportunities
to build on the work of others. This does NOT mean it’s
okay to copy someone else’s code and say that it’s your
own. Instead, you should use someone else’s program for
ideas, or copy only a small part of the code.
ATTRIBUTION
You should always give by making sure
that the programmer gets credit for their work. If your
program or part of your program was written by you but
inspired by someone else, give them
credit in a comment or README
THIS PART
file. If you want to copy part
IS MINE.
of someone else’s program,
first ask the author if it’s
okay or look for copyright
permissions. Then, make
it clear which part is
their code and which
101
part is yours. When you’re copying code, it’s a good idea to
include attribution in both a comment and a README file.
Here’s an example of what giving attribution looks like:
I used the example project from @the_coding_master, and I
modified it to use more light effects, added a turtle costume
to the whole thing, and made it play the music from @music_
lover. Credit to @gamer_pro for the game play inspiration!
WHOA! DID YOU
MIND IF I COPY
MAKE A PROGRAM THAT
THAT CODE?
DOES YOUR HOMEWORK
FOR YOU? I'LL GIVE YOU
ATTRIBUTION.
When you give attribution, you are showing that you are
grateful for someone else’s hard work and you are helping
to create a community of sharing. Also, giving attribution
isn’t just a nice thing to do-in some cases, it’s also the law!
102
Giving attribution in programming is like CITING
quotations or PARAPHRASING other authors when
you write a report in English class.
PARAPHRASE
CITE
Using someone else’s idea but
Referencing the source
saying it in your own words
USING LIBRARIES
LIBRARIES
(also known as modules or extensions) give you
PREMADE FUNCTIONS
access to helpful . For example,
if you were making a game, you could type hundreds of
lines of code to simulate a character jumping around and
interacting with another character on the screen. Or, you
could use a library that already has all the jumping-and-
interacting-with-characters
PREMADE
code built in. Some libraries
FUNCTIONS
require that you give attribution
Ready-made lines
somewhere in your program,
of code for a
sometimes as a comment in specific action
your code.
It’s always a good idea to look for help or a library
that can support your project.
103
THIS ISN’T
THE LIBRARY
I WAS
THINKING OF.
104
w
1. Name two benefits of programming as a team.
2. True or false: Most programmers never need to ask
for help.
3. It’s okay to use someone else’s code as long as you do
what two things?
4. If you don’t copy someone’s code exactly, but use it as
inspiration, do you still need to give credit? Yes/no.
5. As the driver, how can having a navigator help you?
6. Why would it be important to switch roles often when
pair programming?
7. Why would using a physics library (one that has
functions that can make your characters and objects
look like they are realistically interacting or moving)
be helpful to a game maker?
More questions 105
Any two of the following are good benefits:
• You can accomplish bigger tasks.
• You have a variety of strengths to draw from.
• You have extra sets of eyes to help avoid and
catch mistakes.
• You can learn from others.
Many programmers would feel sad or even angry about
someone else claiming authorship of their code.
Unit
4
Algorithms and
Programming
110099
11
Chapter
USING
ALGORITHMS
ALGORITHMS
Both humans and computers use algorithms. Algorithms
are processes or steps that can be followed. A recipe is
an example of an
algorithm that both
humans and some
computers can use.
Algorithms give
clear instructions
for repeating tasks.
Different algorithms
could be used to
complete the same task. For example, there are different
ways to divide two numbers using long division or by doing
repeated subtraction. Both ways give you the same result,
110
but one way may be better. In computer science, we are
always looking for better algorithms.
Better algorithms are faster, simpler, or more efficient.
Algorithms are useful because they can
provide better ways to complete tasks.
Efficient
Inefficient
(the opposite of efficient)
Studying Algorithms
Developing algorithms is its own branch of computer science
and is very similar to the study of mathematics. For example,
mathematicians and computer scientists have been studying
111
the TRAVELING SALESPERSON PROBLEM for almost
100 years.
The Traveling Salesperson problem asks, “Given a list of
cities and the distances between each pair of cities,
what is the shortest possible route that a salesperson
can take to visit each city and return home?”
The goal of the Traveling Salesperson problem is to develop
the most efficient algorithm that can determine the shortest
path that a traveling salesperson should take. The problem
can be applied to real life. For example, a delivery truck
dispatcher uses a shortest-route algorithm to determine all
their deliveries for the day. The algorithm helps the trucking
company save time and money.
PROGRAMS
The job of a computer scientist is to come up with a solution
to a problem, turn the solution into an algorithm, and then
code the algorithm into a program so that it can be read by a
computer. A program is an algorithm that has been translated
(coded) into instructions for a computer.
Algorithms are often written out in a way that most people
can understand. It’s less likely that most people can read
112
a computer program and understand it, because it uses
a combination of numbers, letters, and symbols in an
arrangement we are not used to-but a computer would
know just what it says.
Programmers give very specific instructions to computers
PROGRAMMING LANGUAGES
using . Programming
languages use combinations of numbers, words, symbols, and
formatting to tell a computer what to do in a way that it
can understand.
FOR EXAMPLE:
Suppose you wanted to find out if today
is your friend's birthday. You could write this algorithm or
program.
ALGORITHM PROGRAM (PYTHON)
1. Look up today’s date. #Import datetime library
from datetime import *
2. Ask a friend when #Get Today's Date
their birthday is. today = date.today( )
3. D etermine if today is #Get User’s Birthday
your friend’s birthday. dob_str = input(“What is your
Date of Birth? dd/mm/yyyy")
113
ALGORITHM PROGRAM (PYTHON)
4. I f today is your friend’s #Convert user input into a date
birthday, say “Happy dob_data = dob_str.split("/")
Birthday!” Otherwise, tell dobDay = int(dob_data[0])
them, “Today is not your dobMonth = int(dob_data[1])
birthday.” dobYear = int(dob_data[2])
dob = date(dobYear,dobMonth,dobDay)
user’s birthday
thisYear = today.year
nextBirthday =
date(thisYear,dobMonth,dobDay)
if today == nextBirthday:
print("Happy Birthday!")
else:
print("Today is not your birthday.")
When you start learning
to program, it’s traditional HEY
to begin by writing a
simple program that makes
a computer display,
“Hello, World!”
114
EARLY DAYS OF PROGRAMMING
Programming a computer is also called coding. Coding can
be traced back to the nineteenth century.
Ada Lovelace is considered one of
THE FIRST PROGRAMMERS. In 1843,
Lovelace wrote an algorithm for
a machine called the ANALYTICAL
ENGINE, which was a mechanical
computer.
Augusta Ada King,
Countess of Lovelace
The Analytical Engine
was designed by
CHARLES BABBAGE.
Instead of running on
electricity like modern
computers, this computer
used gears and a steam
engine. It was used to
count and solve simple
mathematical problems.
The Analytical Engine
115
The Analytical Engine was designed
to run simple programs made using
punch cards. Each punch card would
have holes in it that the machine
would read as instructions. The
punch cards would be used to
punch cards
program the computer.
Lovelace believed that the machine could be given
instructions to carry out other tasks. She understood that
it could be programmed. Lovelace was the first person to
recognize the potential of the Analytical Engine beyond
calculating.
116
w
1. Explain the difference between an algorithm and
a program.
2. Which of the following is NOT an algorithm?
A. Steps to make a burrito
B. Instructions on how to French braid
C. A how-to guide on building a model airplane
D. An anonymous love note to your crush
3. Why are the best algorithms efficient? Why are
computer scientists always looking for more efficient
algorithms?
4. Choose the algorithms below that are also programs.
A. Instructions on how to play an instrument
B. Microsoft Word
C. Snapchat
D. A list of steps for building a drone
5. True or false: Different algorithms can be made to
complete the same task in different ways.
6. What kind of languages do computers understand?
More questions 117
An algorithm is a set of instructions to complete
a task, and a program is a set of instructions
that can be understood by a computer.
Computers need specific instructions and only
understand programming languages.
12
Chapter
PROGRAMMING
LANGUAGES
There are hundreds of programming languages, and
programmers use different languages for different types
of tasks. Languages like JavaScript, PHP, and Python
WEB PAGES
| are used to make -documents that can be | | |
| ----------------------------------------- | --- | --- |
displayed in a web browser (like Chrome, Safari, or Firefox).
| A collection of web pages is called a | WEBSITE | . |
| -------------------------------------- | --------- | --- |
MOBILE APPLICATIONS
are MOBILE
| made with the programming | APPLICATIONS | |
| --------------------------- | ------------------ | --- |
| languages Swift, Java, C, | Types of software | |
designed to run on
and others.
mobile devices like
cell phones and tablets
121
USING PROGRAMMING
LANGUAGES
Since each programming language has different strengths
(for example, some are faster, others are easier to write, or
some show graphics better), programmers may use several
languages for large projects. For example:
Facebook uses Python, JavaScript, PHP, and others.
YouTube uses Python, JavaScript, C++, and others.
Twitter uses JavaScript, C++, Ruby, and others.
All three websites use JavaScript. That’s because
JavaScript (along with HTML and CSS) is primarily a
FRONT-END LANGUAGE, which means it is used to make
the part of a website that can be viewed on a screen.
Websites like Facebook, YouTube, THIS TIME YOU GET
TO BE THE BACK HALF.
and Twitter also store tons of
information (posts, comments,
profile pictures, videos, etc.).
This means they need another
type of programming language
(a BACK-END type) to organize
and connect all the extra
information to the front end.
122
Different back-end languages are used for different
reasons. For example, C++ runs (follows instructions) faster
than other programming languages but is harder to write.
So a company might start by writing their product in an
easier language like Python and then go back and replace
parts of the product with C++ to increase the speed at which
it processes information.
No computer programmer knows every programming
language, just like no one knows every spoken language.
However, it is useful to know a few programming languages so
that, for example, you can combine a language that is great
for graphics with a language that is great for processing large
amounts of code.
HOW COMPUTERS READ CODE
LANGUAGE A COMPUTER
CODE =
UNDERSTANDS
Binary
Computers process information using electrical circuits
that can turn on and off. Computer scientists use
the digits 1 and 0 to stand for
A path or collection
of paths through which
on and off. The 1s and 0s
electricity is carried
are a type of encoding called
123
BINARY MACHINE CODE
, or .
BINARY
A binary digit can be either 0 or 1. Binary is how
computers talk and
represent information.
In binary, 1s and 0s are often used,
but you can also represent binary
with “On” and “Off” or “True” and
“False.” All words, numbers, letters,
1 = ON
symbols, images, videos, programs,
0 = OFF
emojis, and music can be
represented in binary.
MACHINE CODE
The most basic language that all
programming languages are turned
into before a computer runs them
The CPU of a computer can only read instructions written
in machine code. So, after a human enters a program into
a computer, a computer program
then turns it into binary machine COMPILING
Translating a
code. The process of translating
programming language
(changing) a program into machine
into machine code
COMPILING
code is called .
124
No matter how many different programming languages are
used to write the phrase “Hello, World!”, the machine code
for each version looks the same.
PROGRAM
print("Hello, World!")
I CAN
READ
THIS!
COMPILER
INPUT:
Algorithm ➜ Code
MACHINE CODE
01000101
PROCESSING
MACHINE
BINARY =
CODE
A compiler changes instructions from the programming language
into machine code. Before the first compiler was invented,
programmers had to write their programs in a language close to
machine code. In 1952, GRACE HOPPER wrote the first compiler
program. Her compiler helped programmers spend less time
writing out machine code and more time creating programs.
125
Representing Numbers Using Binary
Binary is another way of using numbers to count or to
represent numbers. Binary is sometimes referred to as
BASE 2 because it uses two digits (0 and 1), while our usual
way of counting is called BASE 10 because it uses ten digits.
The bi in binary means two. Even though binary
uses only two digits, it can still be used to
represent every number value that base 10 can.
I'LL GIVE YOU
HMM. I WONDER WHY
TEN GUESSES.
WE COUNT IN BASE 10?
In base 10, each place is ten times the value of the place to
its right. As numbers get larger, we add digits to the next
place value to the left.
126
| FOR EXAMPLE, | the number 237 means two hundred |
|---|
thirty-seven. Each digit corresponds to a value that is
based on the place of the digit in the number.
| 100s | 10s 1s | | |
| ---- | ------ | --- | --- |
| 2 | 3 7 | | |
binary = 2
In binary, numbers increase in value 2 times as we double
(multiply by 2) the value of each new place. From right to left,
digits in base 2 (binary) have the place values of 1, 2, 4, 8, 16,
32, 64, and so on, doubling each time.
Binary place values: From right to left, each place is double
the value of the previous one.
To represent the number 1 in binary, write “1” in the ones place.
| 128s 64s | 32s 16s | 8s 4s | 2s 1s |
| ------------ | ----------- | ----------- | ----------- |
| place place | place place | place place | place place |
1
127
There is no “2” digit in binary. To write the number 2, put a
0 in the ones placeholder, then move to the left and put a 1 in
the twos place.
| 128s 64s | 32s 16s | 8s | 4s | 2s | 1s |
| ------------ | ----------- | ----- | ----- | ----- | ----- |
| place place | place place | place | place | place | place |
| | | | | 1 | 0 |
| | | | | ON | OFF |
0 is in the ones place, so its value is 0 × 1, or 0.
1 is in the twos place, so its value is 1 × 2, or 2.
When you add together the two values (0 + 2), you get 2.
You can use basic addition to figure out binary values.
| 128s | 64s 32s 16s | 8s | 4s | 2s | 1s |
| ------ | ----------------- | ---- | ---- | ---- | ---- |
VALUE
| place place | place place | place | place | place | place |
| ----------- | ----------- | ----- | ----- | ----- | ------- |
| 3 | | | | 1 | 1 2 + 1 |
| 4 | | | 1 | 0 | 0 4 + 0 |
| 5 | | | 1 | 0 | 1 4 + 1 |
| 6 | | | 1 | 1 | 0 4 + 2 |
128
Another way to think of binary digits is how computers do:
as “on” or “off.”
FOR EXAMPLE,
if we had 8 light bulbs lined up in a row
(to represent 8 place values in base 2), we could use them
to represent a number in binary by turning each light bulb
on or off.
You can represent 237 using a row of 8 light bulbs. Each
light bulb that is on represents 1, and each light bulb that is
off represents 0 value in the placeholder.
1 1 1 0 1 1 0 1
The sum of the place values for the light bulbs that are on
is 237.
128 + 64 + 32 + 8 + 4 + 1
129
Representing Letters in Binary
At first, computers were used just to make mathematical
calculations. Later, a way to represent letters and symbols
in binary was developed.
The AMERICAN STANDARD CODE FOR INFORMATION
INTERCHANGE (ASCII) assigned each letter of the alphabet
and symbol its own binary code. Each letter was assigned
a number, which was then encoded into binary.
For example,the capital letter A is assigned the number 65,
which in binary is written 01000001.
Although the number 65 and the letter A share the exact
same binary code, the program tells the computer if it
should interpret the binary as letters or numbers.
130
Bits and Bytes
Bit is short for
binary digit.
Terms like “16 gigabytes of memory”
or “1 terabyte hard drive” are
used when talking about computer
WHAT
storage. These terms represent A CUTE
LITTLE
quantities of binary digits. BIT!
BIT
A is the smallest unit of
storage. It represents one digit
(1 or 0).
The next greater
BYTE
measurement is a ,
which represents 8 bits. For
example, 01010101 is 1 byte.
(There are 8 digits.)
A BYTE-SIZED FAMILY
b = bit
B= byte
The largest number you can represent with
1 byte is 11111111, which in base 10 is 255.
That’s why RGB (color) values run from 0 to 255: because
those are the numbers you can represent with 1 byte.
131
Larger quantities of bytes can be represented using
a prefix:
Kilobyte (KB)-about one thousand bytes (A 5-page
Word document is around 100 KB.)
Megabyte (MB)-about one million bytes (Audio files are
several MB.)
Gigabyte (GB)-about one billion bytes (HD movies are
a few GB.)
Terabyte (TB)-about one trillion bytes
(Some new hard drives hold around
1-3 TB. The Hubble Space Telescope
sends 10 TB of data to Earth
every year.)
The Hubble Space Telescope was the first major
telescope to be placed in space. Launched into
Earth’s orbit in 1990, it is one of the largest
telescopes ever made. Its purpose is to allow
scientists to observe distant stars and planets.
132
CREATING ALGORITHMS
Before typing out a program, programmers first come up
with the algorithm, or list of steps, that will be used in
PSEUDOCODE
the code. They often use (pronounced
FLOWCHARTS
“SOO-doe”) and
FLOWCHART
to design or plan algorithms
A diagram that outlines
before they begin programming. the steps in a process
Pseudocode
Pseudocode is written in a style or format that’s similar
to the programming language a programmer is going to
use. There are no rules on how to write pseudocode, but it’s
meant to be read by humans, not a computer.
Most programmers format their pseudocode so that each
line represents a line of real code in their final program.
The pseudocode doesn’t have to
be perfect; it should just give an Coding without a plan
is like building a house
idea of what the final program
without a blueprint.
may look like.
133
Flowcharts
Flowcharts help programmers visualize the steps in an
algorithm. Just like making an outline before writing an
essay, flowcharts help organize ideas, and they use specific
symbols to represent different parts of an algorithm.
Each symbol in a flowchart has a meaning.
| NAME | SYMBOL | MEANING IN FLOWCHART |
| ------------- | ------ | ----------------------------------- |
| Oval | | The beginning or end of the program |
| Parallelogram | | An input operation |
A process to be carried out
| Rectangle | | (addition, subtraction, division, etc.) |
| --------- | --- | --------------------------------------- |
A decision (or branch) to be made; the
Diamond
program should continue along one of
the two routes
Hybrid
An output operation
| Flow line | | The direction of flow in the program |
| --------- | --- | ------------------------------------ |
134
If you wanted to write an algorithm to check if today is
your friend’s birthday, the flowchart might look like this:
Look up today’s date.
true false
Is today’s month and
day the same as your
friend’s birthday?
Say, “Don’t forget to Say,
wish your friend a “No reminders
Happy Birthday today!” today.”
It might look like this in pseudocode:
Look up today’s date.
If the month and day of your friend’s birthdate
are the same as today’s date:
Then, say “Don’t forget to wish your friend
a Happy Birthday today!”
Else, say “No reminders today.”
135
w
1. What is a programming language?
2. For computers to be able to read and run a program,
a is needed to translate the program into
machine code.
3. What do the 0 and 1 in machine code represent?
4. Why are there different programming languages?
5. Why might learning one programming language make it
easier to learn another?
6. How many bits are in a byte?
7. If a computer compiled two programs that both wrote
“Hello, World!”, would the machine code for “Hello,
World!” look different?
136
A programming language is a language used
to give specific instructions to computers.
13
Chapter
COMPUTATIONAL
THINKING
Computer science focuses on using computers to create
solutions to problems.
COMPUTATIONAL
THINKING
is the thought
PROCESSING
process for creating solutions
that can be carried out by
a computer.
139
FOR EXAMPLE,
if your problem is that you need to write
a book report, a common solution is to read the book, plan
out the essay, then write about what you read.
A way you might solve the same problem using computational
thinking might be to collect data on the number of times
each character talks to another and plot the information on
a graph. You might even develop a program that analyzes
the data for you. The graph would give you data-driven
evidence of the relationships between the characters in the
story. The output of your program and data could be used
to tell you what to write in your essay.
An extreme example may be to program an artificial
intelligence (AI) program that can understand
natural language, analyze the book, and write the
essay for you. While this example might not help you
meet your goal of learning about the book, it shows
how far computational thinking can go.
The way people
speak to each other
140
In computer science, artificial intelligence (AI) is a powerful way
of programming machines and computers so they can learn from
large amounts of data to improve the way they work. This type of
computing allows computer programs to make predictions and
decisions beyond those that they are directly programmed to make.
There are four major ideas in computational thinking:
1.
Decomposition: Breaking a problem down into
simple parts
2.
Pattern Recognition: Identifying what different
problems have in common
3.
Abstraction: Separating details that matter from
details that are not important
4.
Algorithm Design: Creating a solution with simple
steps that anyone can follow
DECOMPOSITION
Before beginning work on a solution, you need to understand
all the parts of the problem. Once you understand each part,
you can break the problem into smaller tasks. Decomposition
makes problems more manageable to solve.
141
FOR EXAMPLE,
when writing a book report, you would
break the assignment down into smaller, simpler tasks:
1.
Read the book.
2.
Identify the main characters.
3.
Identify the theme.
4.
Analyze tone, plot, and character relationships.
5.
Write about the tone, plot, and characters in the book.
Decomposition helps to identify where to start and the tasks
that need to be completed.
PATTERN RECOGNITION
Patterns are events that are repeated. Recognizing where you
have created solutions to similar problems before will help you
create solutions that can be used to complete different tasks.
FOR EXAMPLE,
if you’ve used a format or a template for
writing book report outlines in the past, you can include that
same process in your program. A book report outline may be
different, but the process of writing the report is the same.
142
ABSTRACTION
Abstraction is focusing on the important ideas of a problem
and ignoring details that will not help you find a solution.
FOR EXAMPLE,
focusing on the important parts of the
book (like the relationships between major characters,
the setting, or the theme), and not on less important
information (like conversations between minor characters
or daily events), helps you create a program that is not
specific to one book. The program would work with books
that have different plots, but include major characters,
settings, and themes.
ALGORITHM DESIGN
Algorithm design means writing out the steps you need to
follow so that you can get the same solution every time.
When a solution is carried out by an algorithm, the solution
becomes reusable.
143
Learning to Code
PROGRESS CHART
KNOWLEDGE
SLLIKS
144
w
1. What is computational thinking?
2. Why is creating a solution that can be reused
an important part of computational thinking?
3. Do programmers use computational thinking while
creating programs?
4. Which one of the four parts of computational thinking
talks about focusing on the main idea?
5. Explain what decomposition is.
6. Which of the four parts of computational thinking is
considered by most to be the key idea?
answers 145
Unit
5
I'M A FREE
SPIRIT KIND OF
PROGRAMMER.
Universal
Programming
Principles
114477
14
Chapter
VARIABLES
VARIABLE
In math, a is a letter or symbol used in place of
a quantity we don’t know yet. The variable is a placeholder
for a number in a mathematical expression or equation. In
computer programming, a variable is a container for storing
a value. The variable is stored in the computer’s memory and
can be used or changed throughout the program. Variables
act as stand-ins or placeholders for values that are stored
in the computer.
IDENTIFIER
The name of the variable is the . The information
VALUE
that the variable contains is the . Variable values
can be text, numbers, or other types of data.
For example, the score in a computer game is the variable.
If the game starts out at
Value
12
zero and the player earns one
point, here’s how the variable SCORE Identifier
would work:
Variable
148
The program finds where the variable value for “score” is
stored, then replaces the previous value of 0 with the new
value: 1.
ASSIGNING AND
NAMING VARIABLES
To create a variable within a
DECLARE
DECLARE
program, you have to
To create a variable
it. When you declare a variable, within a program by
giving it a name
you’re telling the computer to
create a space for information
and to assign that space a name. It’s like organizing a
bunch of toys using boxes on a shelf. For each type of toy,
you pick a box, label it, and put the toys inside the box.
149
I DECLARE THIS
BOX TO BE FOR
BASEBALL
CARDS!
BASEBALL
CARDS!
CLEATS
OLD NEW
HATS HATS
FOAM FOAM
HANDS HANDS
(OVERSIZED) (UNDERSIZED)
To assign a value to a variable, use the equal sign (=). The
identifier goes on the left of the equal sign, and the value
goes on the right. You can assign a new value to your
variable anytime you want.
The = symbol is called ASSIGNMENT
an ASSIGNMENT OPERATOR
OPERATOR The = symbol, which assigns
in
values to variables
programming because it’s
used to assign a value to
a variable.
150
In programming, the = sign doesn’t mean “equals”; it means
“is assigned.”
name = "Jason" means that the variable name is assigned
the value Jason.
There are specific rules for how you can identify or name
variables. Different programming languages may have
different rules, but the common rules are:
Variable names should be short and should clearly
describe what the variable represents.
This works: score
Too long!
This doesn‘t work: this_variable_represents_
player_1_score
Variables must begin with a letter of the alphabet.
This works: firstPlayer
This doesn‘t work: 1stPlayer
151
Variables can contain letters, numbers, and some
characters like an underscore. No reserved characters (like
more than one word to name a variable, you can use the
underscore (_) symbol instead of a space or use uppercase
letters to start each word with no space between words.
These work: first_player or firstPlayer or
FirstPlayer
These don’t work: first player or first#player
or first@player
Some words already have special meanings within a
program and cannot be used as identifiers. These words
depend on which programming language you are using.
FOR EXAMPLE,
Python uses the word “return” to produce
a value of an expression or function. Here are some
reserved words (words you can't use for naming) in Python:
PYTHON RESERVED WORDS
true for false import and
not if or else return
none while elif
152
TYPES OF INFORMATION
VARIABLES CAN STORE
Variables can store many different types of information
(called data types).
I CAN
String Values STORE
ANYTHING.
STRING
variables can store
any kind of character (including
letters, numbers, symbols, and
special characters). For example, in
a quiz program, we could use string
variables to store questions and
answers in the program.
“”
A string is always placed inside
quotation marks.
EXAMPLES:
String
name = "Alan Turing"
fruit_salad = "Yummy yummy"
Variable name (Identifier)
153
Numeric Values
Variables can also store numeric values, including integers
(positive and negative whole numbers) or floating point
numbers (numbers with a decimal point). For example, we can
use a variable to store the amount of time it takes a player
to complete a level in a game.
Do not use quotation marks with numeric values.
EXAMPLES:
Numeric value
age = 13
Variable name (Identifier)
xp = 245
HIGH
score = 23.5
SCORE!
x_coordinate = -300.76
XP = EXPERIENCE POINTS
Used to show a player’s character’s
advancement in a video game
154
You can use algebraic expressions when assigning values to
variables. For example, we can use a variable to store the
experience points a player has and add 5 points to the value
every time they reach a goal (score = x + 5).
We could also use math to add points to a score variable.
FOR EXAMPLE,
to add 2 points to a value we can use:
score = 5 + 2
Because “score” is an integer variable, it has the value of 7,
the sum of the integer values.
But if you made “score” store a string by putting 5 + 2 inside
quotation marks like this:
score = "5 + 2"
Then “score” is storing the string value of "5 + 2", the actual
content within the quotes.
155
Boolean Values
Sometimes programmers need to know if something is true
or false. For example, in a game they want to know if the
game is over or if it is still
going. Or, did the user get a Boolean variables
quiz question right or wrong? are named after the
English mathematician
When the information we want
George Boolean.
to store is true or false (can
TRUE!
also be “yes” or “no”), then we
can use another data type
BOOLEAN
called (pronounced
“BOO-lee-un”). Boolean variables
can only have two possible
values: true or false.
FOR EXAMPLE:
I_like_licorice = False
powerUp = True Variable name (Identifier)
gameOver = True Boolean
value
156
Lists
ARRAY
An variable stores an entire list of information. This
is useful when you have multiple pieces of information that
you want to store in one place. For example, in a Hangman
game program you could use a list (array) to store all the
letters the player guesses. Each time the player guesses a
new letter, it would be added to the end of the list.
157
w
1. In computer science, variables:
A. are numbers like pi
B. represent parts of an experiment that are measured
or tested
C. are placeholders for storing information
D. are unchangeable
2. What is the difference between a variable’s identifier
and its value?
3. Explain what it means to declare a variable.
4. Which of the following variables are string types?
(There may be more than one.)
A. character = “Dr.”
B. vehicle = “Ambulance”
C. speed = 37
D. lives = “3”
158
What is the assignment operator? What does it do?
C
The assignment operator is the = symbol. It is used to
assign values to variables.
15
Chapter
CONDITIONAL
STATEMENTS
Conditional statements run a chunk of code only when a
certain condition is met. Conditional statements follow the
IF . . . THEN FORMAT
(if this, then that), and they allow
programs to be more flexible and powerful because they
can change depending on different conditions.
For example:
If you touch the enemy, then your character dies.
If you cross the finish line first, then you win.
If you score a goal, then your score increases by
one point.
163
Here’s what a basic conditional statement looks like:
If a specific thing happens
Then this other thing will happen
Here’s what a conditional statement could look like in a
quiz game:
condition
If the player gives the correct answer
Then the player earns 100 points consequence
(action)
An If . . . Then statement can be shown with a flowchart.
For example, in the quiz game where a correct answer earns
the player 100 points, a basic conditional statement might
look like this:
IF
THEN
Correct answer
Get 100 points
164
You can have a different action happen if your condition is
ELSE
false. To do that, use and then describe the different
action.
If a specific thing happens
Then this other thing will happen
Else
A different thing will happen
Here’s what a conditional statement with an “else”
consequence could look like in the quiz game:
If the player gives the correct answer
Then the player earns 100 points
Else
The player loses 50 points
An If . . . Then . . . Else statement
can also be shown with a
IF
flowchart. For example:
ELSE THEN
Correct answer
Lose 50 points Get 100 points
165
You can combine multiple conditional statements to create
ELSE IF
even more consequences. To do that, use in an
“if” statement.
Every “else if” added within a statement adds another
action, or consequence, that could happen. For example, here’s
how you can use an “else if” to get three consequences (three
different actions) to happen in a conditional statement:
If a specific thing happens
this other thing will happen
Else if another thing happens
A different thing will happen
Else
Yet another thing will happen
Here’s what an if statement with an else if consequence
and an else consequence looks like when calculating the
number of points a player should get depending on
the number of quiz questions they get correct:
166
If a player answers 10 questions correctly
Player is awarded 100 points
Else if player answers 5 or more questions correctly
Player is awarded 50 points
Else
Player is awarded 10 points
The flowchart would look like this:
Start
IF
10 correct THEN
Get 100 points
answers
ELSE IF
5 or more THEN
correct answers Get 50 points
ELSE
Get 10 points
167
COMPARISON OPERATORS
COMPARISON OPERATORS
(symbols used when
comparing values) are used in programming to form
Boolean expressions.
OPERATOR DESCRIPTION
is greater than
< is less than
= is greater than or equal to
<= is less than or equal to
== is equal to
!= is not equal to
Put a value on either side of a comparison operator to make
a Boolean expression.
168
FOR EXAMPLE:
| 10 > 5 | True | 10 <= 5 | False |
| ------- | -------- | -------- | -------- |
| 10 < 5 | False | 5 == 5 | True |
| 5 >= 5 | True | 10 != 5 | True |
“==” means equal to,
just like “=” in math.
Comparison operators can be used in flowcharts. This
flowchart shows that if 10 is greater than 5, you‘ll say “yay,”
else you‘ll say “boo.” You’ll say “yay” because 10 > 5 is True.
| | False | | True |
| --- | ----- | --- | ---- |
10 > 5
| Say “boo.” | | | Say “yay.” |
| ---------- | --- | --- | ---------- |
yay
169
You can use the == operator to compare two values. For
example, you could see if a game is over or not based on
the player reaching a score of 10 like this:
False True
score == 10
Game in progress Game over,
player wins
You could also use a Boolean variable by itself.
For example, in a race game, you could have a variable
called “boost.” The value of the variable is set to True if the
player earns a speed boost. The program uses a conditional
statement to check if boost is true (the player has earned a
boost). If so, then the program should increase the player’s
speed:
True
Boost earned?
Increase
player’s speed
170
COMPOUND CONDITIONALS
To check if multiple conditions are true in one conditional
statement, you can combine Boolean expressions within a
single conditional statement.
COMPOUND CONDITIONALS
are conditionals that
combine two or more Boolean expressions.
LOGICAL OPERATORS
are used to combine the expressions.
The most common logical operators are AND, OR, and NOT.
AND statements are true when both conditions are true.
True AND True → True
For example, if a player finishes a race and if they finished
faster than anyone else, they are the first-place winner.
But if one or both of the conditions is false, then the AND
statement is false.
True AND False → False
False AND False → False
171
FOR EXAMPLE,
a game player sets a new speed run
record only if they beat the game AND finish in less time
than the current record.
If the player just finishes the game but doesn’t do it in less
time, or doesn’t finish the game at all (if both conditions
are not met), then the player does not set a new record.
Beat game
True
AND
time < 9.58 minutes
Player set new
speed record
The OR statement is true if at least one of the conditions
is true.
False OR True → True
True OR True → True
False OR False → False
172
| FOR EXAMPLE, | in a ball game, if the player hits the |
|---|
right wall OR if they hit the left wall, then they lose and
the game ends.
If either condition of hitting either wall is met, then the
consequence (losing) becomes true.
| | Hit left wall | True |
| --- | -------------- | ---- |
OR
Hit right wall
Game over
The NOT statement doesn’t compare two conditions; instead,
it reverses the value from True to False and False to True.
| NOT False | → True | NOT switches the |
| ------------ | --------- | ----------------- |
expression to its
opposite.
| NOT True | → False | |
| ----------- | ---------- | --- |
173
FOR EXAMPLE,
in a race game, we could have a
conditional that says: If Game Over is NOT true, then play
background music. In other words, play music as long as
the game is still going.
IT’S OPPOSITE
DAY.
NESTED CONDITIONALS
NESTED CONDITIONAL
A is one conditional inside of
another conditional. For example, in a virtual pet game you
could nest conditionals to determine the mood of the pet
based on different conditions like hunger and tiredness.
If the virtual pet is not awake, show the mood as asleep.
174
If the pet is awake, and if the pet’s hunger is below 50 percent,
then show a happy mood, else show a hungry mood.
So, if the pet is awake and its hunger level is at 75 percent,
then its mood will be hungry.
The flowchart looks like this:
False True
Pet is awake
False True
Hunger > 50%
Mood = Asleep Mood = Happy Mood = Hungry
175
w
1. What is the difference between an “if” statement and
an “else if” statement?
2. Assume a player scored 15 points by the time they
completed a game. Does the following evaluate to true
or false?
Player score > 20 AND Player completed game
3. Assume an alien in a game has been aggravated and is
200 feet away from the player. Would the alien attack
the player based on the following conditional statement?
If alien is aggravated OR if alien is within 100 feet
Then attack player
4. When would you use an “else if” statement versus
nested conditional statements?
5. Circle the part of the pseudocode below that is the
conditional part of the statement:
If it is summer
Then display “Swimming Pool Open!”
176
An “else if” statement is always nested within
an “if” statement and doesn’t exist on its own.
An “if” statement can exist without an “else if”
statement.
16
Chapter
LOOPS
LOOP STATEMENTS
allow you to easily repeat a chunk
of code many times. For example, in a game with a bouncing
ball, it would be too much work to type out the code to make
the ball bounce up and down a thousand times (move up,
then fall down; move up, then fall down; move up, then fall
down . . .). Instead, you can put the repeated code in a loop:
Repeat 1,000 times
move up, then fall down
BOING!
Loops not only save programmers time, they also make
programs shorter, which makes them easier for the
computer to run.
179
When creating a loop, you should answer these questions:
* What do I want to repeat?
* When do I want the loop to stop repeating?
There are different types of loops:
FOR LOOP
A is a type of loop that repeats itself a
set number of times. For loops are used when you know the
number of times you want to repeat something. For loops
and arrays are often used together.
FOR EXAMPLE,
we could use a for loop to list all the
top-ten players of a game whose names are stored in
an array.
an array containing the
names of the top-ten players
Top10 = [“player1”, “player2”, “player3”, “player4”, “player5”,
“player6”, “player7”, “player8”, “player9”, “player10”]
←begin the for loop, repeat the code in
the loop for each item in the Top10 list
for item in Top10:
the code that’s repeated-print out
each name in the Top10 list
print(item)
180
WHILE LOOP
A will run a chunk of code until a condition
is met. This is used when you don’t know the exact number
of times you want the loop to repeat and it depends on
another factor.
FOR EXAMPLE,
in a quiz game you can repeatedly ask
a question until the user gets the correct answer:
while answer is not correct:
Ask the user, “What is the name of the current
Vice President of the United States?”
print “you are right!”
The quiz game would continue to ask
the question until the user got the right
answer, even if it took 100 attempts!
UHH . . .
ATTEMPT
99
181
NESTED LOOP
A is when one loop is put inside another
loop. Nested loops help create more complex repeating code.
FOR EXAMPLE,
you could program background music for
a game using nested loops.
A nested loop can repeat a beat until the game is over. An
inner loop can repeat a bass drum sound 7 times before a
snare sound is played:
OUTER LOOP
Repeat until the game is over:
INNER LOOP
Repeat 7 times:
Play bass drum sound
Play snare sound
In pseudocode, use indenting to show code
that is inside or dependent on other code.
Be careful when using nested loops, because it’s easy to get
confused about which chunks of code should be repeated.
182
The inner loop always has to run through all its sequences
before the outer loop code is run again.
FOR EXAMPLE,
the background music would sound like this:
OUTER
LOOP
Bass drum, Bass drum, Bass drum,
Bass drum, Bass drum, Bass drum,
Bass drum
Snare
INNER
LOOP
Bass drum, Bass drum, Bass drum,
Bass drum, Bass drum, Bass drum,
Bass drum
Snare
Bass drum, Bass drum, Bass drum,
Bass drum, Bass drum, Bass drum,
Bass drum
Snare
The bass sound is played 7 times (running through all
versions of its loop) before moving on to the next line of
code, playing the snare sound. Then the entire outer loop
is repeated until the game is over.
183
w
1. How are While loops different from For loops?
2. When you put a loop inside a loop, it’s called a
loop.
3. If you want to repeat a chunk of code 6 times, you
should use a loop.
4. What will the following print?
Repeat 3 times:
Print “Jump”
Repeat 2 times:
“Duck”
Print “Slide”
5. When will the outer loop in the following pseudocode
stop repeating?
While number of ice cream cones > 0:
Get a cone
Repeat 3 times:
Add scoop of ice cream
184
While loops will repeat as long as a condition
is true, but a For loop will repeat a set number
of times.
17
Chapter
EVENTS
EVENTS
are actions that cause something to happen
within a program. They make programs interactive because
the user is in control. For example:
clicking a mouse
pressing a key
tapping a touch screen
187
Events can also be things that happen within the program-
like when a character dies and the message “Game Over”
appears.
Events can be external actions from a user, like a mouse
click. They can also be internal actions that happen within a
program, like a web browser completely loading a web page.
EVENT HANDLER
An is the code that is run when an
event happens. Pressing the spacebar in a game is an event,
but the event handler is the code in the game that tells a
character to jump when the spacebar is pressed.
FOR EXAMPLE,
in a fruit-chopping game, you could add
code like the pseudocode below that swings a chef‘s knife
every time the spacebar is pressed.
on press_spacebar:
swing chef‘s knife
188
w
1. Give an example of an event from a keyboard.
2. How is the event handler different from an event?
3. What would your favorite app be like without events?
4. What is the event in the following pseudocode?
on-screen tap:
If player tapped balloon:
Pop balloon
5. What is the event handler in the following pseudocode?
on-screen tap:
If player tapped balloon:
Pop balloon
answers 189
18
Chapter
PROCEDURES
REUSING CODE
PROCEDURE
A is a piece of code that you can easily use
over and over. Loops are great when you want to repeat an
action multiple times in a row. But when you want to use the
same chunk of code in different parts of a program, you will
need a procedure.
For example, in a four-person game we could program each
character individually to jump when each player presses
their jump button. But a better
PROCEDURE
way is to create a single jump
A piece of code that has
procedure for each character to
a name and completes a
use when each player presses specific task
their jump button.
Declaring a Procedure
Instead of copying and pasting the same chunk of code
throughout a program, a programmer can save that
chunk of code and name it. When the name of the code
191
(the procedure) is used in a program, the computer
understands that it should use that chunk of code.
HIS MAJESTY HAS
To create a procedure, you
DECLARED A NEW
must declare it by giving it PROCEDURE . . .
a name and adding the code
you want to use as a procedure.
(It‘s like declaring a variable,
where you give a variable
a name and a value).
You could declare a jump
A function is also a chunk
procedure for the four-person
of code. Each function
game by calling it “jump” and performs a specific task,
like “print.”
adding the code to it that makes
a character jump.
name of procedure
function jump
move up
code for the
pause procedure
move back down to the ground
STEP 1: Identify the chunk of code to be saved:
move up, pause, move back down to ground.
192
STEP 2: Name the chunk of code and save:
Jump = move up, pause, move back down to ground.
Calling a Procedure
CALL
Declaring a procedure just gives it
When you use
a name; it won’t run the code. The
the name of a
procedure will not do anything if you procedure in a
program so that it
don't tell it to. When you’re ready to
can run the code
use the procedure in your program,
CALL
you have to it.
For example, a procedure can be called as many times as
you want.
When Player 1 hits the spacebar
Jump
name of procedure
When Player 2 hits the up arrow
Jump
When Player 3 hits the W key
Jump
When Player 4 hits the I key
Jump
193
The same procedure-jump-is called when four different
events happen. When the computer reads “jump,” it will
look up the jump function and run the code found there.
HELLO, I’M
THE . . . WHAT?
CALLING ABOUT
THE PROCEDURE.
YA GOT
ME,
DOC!
Parameters and Returns
PARAMETERS
are variables whose value is passed into a
procedure. It can give limits or ranges to the procedure, like
“jump 3 times.” The only difference between a parameter
and a variable is that a parameter value can only be used
within a procedure, but a variable can be used throughout
the entire program.
A parameter’s input can change how a function acts.
194
FOR EXAMPLE,
in a space battle game we can use a
function to animate a laser shooting out of a spaceship’s
gun. Because we want the laser to shoot at whatever
the user is aiming at and not the same spot every time,
we need to input (to the laser function) the location that
the user is aiming at. The laser function can then change
where it shoots each time the user fires the spaceship’s
gun.
X and y parameters can give the x- and y-coordinates to the
function so the laser shoots in the direction the player is aiming.
Function Shoot_Laser (x,y):
Display laser graphic next to
spaceship gun
While on the screen:
Move toward (x,y)
195
RETURN A VALUE
Some procedures or functions can .
The return value is the procedure output. Depending on the
procedure, you could get a different return value every time
you ran it.
Parameters and return values are often used in the
same function.
FOR EXAMPLE,
if you made a procedure that
calculated the average reaction speed of a game player,
the parameters would be the reaction times of the player,
and the return value would be the average of all the
player’s times.
This is how
This is the task.
the task is
accomplished.
Function Average_Time (Player_Times_array):
Average = Sum all times in Player_Times_array
divided by number of items in array
Return Average
This is the result of the task.
After calling the Function Average_Time,
the function would return a value that is
the player’s average time.
196
w
1. A piece of code that you can easily use over and over
again is called a .
2. What’s the advantage of using parameters with a
procedure?
3. The output of a procedure is called the value.
4. If you want to use the same chunk of code multiple
times in your program, you should make the code a
.
5. What is the return value for the following function?
Score = 5
Function Score_Bonus (score):
Return Score + 10
answers 197
Unit
6
Programming
with Scratch
119999
19
Chapter
GETTING
STARTED
GETTING TO KNOW SCRATCH
Scratch is a free graphical programming language.
It is a programming language that is simple to use
because you don’t have to type in commands.
BLOCKS
It works by snapping precoded together to
create scripts (programs).
Scratch is useful
BLOCK
for making games
A block in Scratch is a graphic that
and interactive represents a chunk of code. Blocks
snap together depending on
stories.
their shape (like puzzle pieces).
200
BLOCKS
Instead of programming by typing out commands, in
Scratch programs are made by connecting blocks together
vertically. All a user has to do is snap blocks together and
their code will run in order from the first block (at the top)
to the last block (at the bottom).
Block
Blocks look like this
Block
Blocks fit together like puzzle pieces and come in several
categories that organize blocks into similar actions. There
are six types of blocks that snap together in different ways
depending on their shape (like puzzle pieces that only fit in a
specific way). The shape of the block doesn’t control what it
does; it only controls how other blocks connect to it.
You can stack a couple of blocks together to make a short
and simple program that will move a character across
the screen. Or you can make a long and complicated
program that uses hundreds of blocks, like for a game
with multiple levels.
201
SOME SAY HE’S BEEN CODING FOR OVER
A HUNDRED YEARS AND HIS PROJECT
USES A MILLION BLOCKS!
The Blocks menu organizes all the blocks into nine categories,
each represented by a colored dot and a category title.
Category
Blocks palette
Blocks
Blocks menu
202
Each category is a grouping of blocks that does similar
things:
Motion, Looks, and Sound blocks control objects in
the program and what they do.
Variables and Operators blocks store and manage
information.
Events and Sensing blocks make specific actions
happen.
Control blocks direct the program, script.
My Blocks allow you to make and store your own
custom blocks.
Scripts
A single group of blocks that are all connected is called a
SCRIPT
. A script can be a very basic program that is two
blocks long, or a million (or more) blocks long. Any number of
scripts can be used together to make a single project. Large
projects such as a multilevel game can use dozens of long
scripts.
When making a script, you can stack blocks together or
place one block inside the other.
203
The green block is placed
when clicked inside the purple block.
say join Hello, name
start sound Meow
Scripts are created in the
SCRIPTS AREA
SCRIPTS AREA
.
The space on the screen where
blocks are combined
to make scripts
Blocks are used by dragging
them over from the Blocks
palette to the Scripts Area.
Drag blocks over
Scripts
Scripts Area
204
You can add COMMENTS
I’M WRITING
by right-clicking (or ctrl-clicking A SCRIPT. ME TOO!
for Macs) directly on a block
or on the Scripts Area and
selecting “Add Comment.”
Comments help
programmers keep
track of what specific
chunks of code do and
Comments are not run
make it easier to share
as part of the code.
code with others.
FOR EXAMPLE,
if you wrote a chunk of code that
slowly subtracted health points from a player in a game,
you could comment on it as a reminder to yourself that
“this code is for the poison effect; it decreases player
health by 5 points every
10 seconds.”
This is what a Scratch
comment looks like.
205
If you’re using the online version of Scratch, you can store
your scripts in the backpack area.
Backpack
Storing scripts is helpful because you can save time and
effort by using the same script in more than one project.
206
FOR EXAMPLE,
you might want to make a game
that has a kangaroo that jumps. If you’ve already
made a game that has a rabbit jumping,
I’M GOING
you could open the rabbit game, TO SAVE THIS
RABBIT SCRIPT
drop the jump script from the
FOR LATER.
rabbit game into the backpack,
open the new game, and
drag the jump script from
the backpack to your new
kangaroo game.
SWEET
CODING
TIP!
207
SPRITES
SPRITES
are the characters and objects used in programs.
You can control sprites with blocks.
Programs can use one or many sprites. Scratch has a
library of sprites. You can also draw or upload your own
sprite.
The SPRITE LIST displays all
THUMBNAIL IMAGE
the sprites used in a project.
A smaller version of
Each sprite is represented by the original image
THUMBNAIL IMAGE
a .
Sprite list
New sprite
menu
Selected sprite
Sprite thumbnails
208
When you have multiple sprites in your program, click on
the thumbnail to select the sprite you want to write a script
for, change the appearance of, or add a sound to.
New sprites can be added to the Sprite list using the New
Sprite menu, where you can Choose a Sprite, Paint, Surprise
(a random sprite from the library is chosen for you), or
Upload Sprite.
COSTUMES
Different images used to
Costumes
change the appearance of
Each sprite can have a single sprite
COSTUMES
multiple .
Costumes let you change how
a sprite looks, like the position of
its limbs, what it’s wearing, or
its size. Costumes can be used to
animate sprites, like the pages in
a flip-book cartoon.
FOR EXAMPLE,
here are four costumes that can be used
to make it look like the sprite is moving:
209
Costumes are edited in the Costumes tab.
Image Editor
Costume list
COSTUME LIST
The shows a thumbnail for each of the
sprite’s costumes. In the New Costume menu, you can:
choose a costume from the library
draw or upload a file
take a picture
You can view the costumes
of other sprites by selecting
the sprite in the Sprite list.
210
IMAGE EDITOR
The has tools to draw new costumes
or edit the costumes of existing sprites. Costumes can be
BITMAP VECTOR
created in either or mode. Both modes
will allow you to create the same artwork, but they are
different in how the image is made.
Bitmap mode: Tools are more recognizable (paintbrush, line,
circle, text, fill, erase, and others) as editing tools, but images
can look grainy when enlarged.
Vector mode: Add, resize, and reshape
shapes by pulling at the corners. Vector
mode creates graphics that are more
smoothly enlarged, making it better
to use for projects that are viewed in
full-screen mode.
211
Sounds
You can program your sprites to play sounds using blocks in
the Sound category.
The Sound list shows all the sounds available for the selected
sprite. You can also add sounds from Scratch’s sound library or
from uploaded music. Or you can record your own sound.
The Sound Editor allows you to edit sounds.
Sound list
Sound Editor
The shape on the screen represents the sound. It changes as
the sound is changed.
212
Setting the Stage
STAGE
The is the place where you can see the output of
running your script. The green flag and the stop sign start
and stop the program respectively.
Start Full screen
Stop
Stage
213
Sprites move around the stage using a grid system like the
coordinate system used in math. The x- and y-coordinates
are used to identify locations.
y
5
4
3
2
1
x
-5 -4 -3 -2 -1 1 2 3 4 5
-1
-2
-3
-4
-5
The x- and y-coordinates at the center of the stage are
(0, 0). The stage is 360 steps tall and 480 steps wide.
(x, y)
214
MOTION BLOCKS
move sprites around. They allow you to
change the x- and y-coordinate positions.
change x by 10
FOR EXAMPLE, Motion
the block
block
will move a sprite 10 steps along the x-axis
(10 steps to the right). You could use the same block but
change the 10 to -10 to move the sprite -10 steps along
the x-axis (10 steps to the left). The “change y by ( )” block
moves a sprite up and down along the y-axis.
HEY! THIS
GRID LOOKS
JUST LIKE THE
COORDINATE
PLANE I
LEARNED
ABOUT IN
MATH CLASS.
215
The background image (scenery)
Tip: Add background theme
on the stage is called the music to a backdrop
BACKDROP . Select the stage to play music while
users play your game!
thumbnail to create scripts for
your backdrop and bring up the
backdrop tab. You can edit backdrops with the backdrop
tools in the backdrop tab. You can add scripts, additional
backdrops, and sounds to the backdrop.
Backdrop tab
Stage backdrop
Backdrop tools
Backdrop
216
Sharing Projects
The online version of Scratch allows users to publish and
share projects with the community. Once a project is shared,
anyone in the world who goes to the Scratch website can
see it.
When projects are shared, community members can leave
comments (questions, positive feedback) on the project pages.
Each project has its own project page where the owner adds
instructions, notes, and credits.
Extensions
EXTENSIONS
can be
EXTENSIONS
used to add more blocks
Additional sets of new
to the palette. blocks that can add
more functions
Extensions include:
* Music blocks that can play notes like musical instruments.
* Pen blocks that can be used to draw on the stage.
* Blocks that add interactive capabilities, like video
sensing, text to speech, and translate.
217
w
1. Describe what a script in Scratch is.
2. What are blocks in Scratch used for?
3. What is the Scripts Area used for and how is it used?
4. If you want to save a chunk of code to use in another
project, which Scratch feature should you use?
5. Which of the following comments would not be
appropriate to post on a project?
A. The project rocks!
B. How did you make the cat sit on the cactus?
C. Great project. FYI I found a bug on level 2 in the game.
D. What a waste of time, you should quit coding now.
More questions 219
A script is a collection of blocks that have been
stacked together. Scripts can be a couple of blocks
or many dozens of blocks long. They can be combined
to create a program.
A. The sprite would move up 100 steps.
B.
The sprite would move to the center of the screen.
C.
The sprite would move to the right 100 steps.
20
Chapter
BASIC
ALGORITHMS
When you run a program in
An algorithm is a list of
Scratch, each block completes
steps to complete a task.
its task before moving on to the
next one in the script. Scripts run
starting with the top block and
working down to the last block.
| 1st when | clicked | |
| -------- | ------------- | --- |
| 2nd move | 10 steps | |
| say | Hello, World! | |
3rd
| 4th start | sound Meow | |
| --------- | ----------------- | -------- |
| 5th ask | What's your name? | and wait |
223
There are two ways to make a script run:
Click on any of the blocks in the script. (This runs
the entire script starting at the top.)
Use an event block.
when clicked EVENT BLOCK
move 10 steps
When a script
say Hello, World! is running, all
the blocks in the
start sound Meow script glow at the
same time.
ask What's your name? and wait
TYPES OF BLOCKS
The most commonly used block types are hat blocks and
stack blocks.
224
HAT BLOCK
A starts the script it is attached to. It does
not have a notch on its top and cannot fit under other
blocks. Hat blocks are event handlers in Scratch-they listen
for events and run when the event happens. For example,
when green flag clicked is one of nine event blocks; it runs
the code attached to it when the user clicks the green flag.
WE’RE ALWAYS ON TOP OF THINGS!
ME TOO!
Examples of events are when a user presses a key on
the keyboard or when a sprite is clicked on.
STACK BLOCK
A is a rectangular block that connects to
other blocks.
ANIMATING A CAT
SCRATCH
The default sprite for every new project is the
CAT
. Sprites can be programmed to move around the stage
using blocks in the Motion category.
225
WHAT ARE YOU
Walk
GOING TO MAKE ME DO?
This script makes the Scratch Cat move
forward 10 steps when the green flag
is clicked.
1, 2, 3, 4, 5,
6, 7, 8, 9, 10
when clicked
move 10 steps
Some blocks have fields in them where you can type in your
own numbers or text.
PARAMETERS
These fields are called . Click on them to
change or add numbers or text to them.
move 10 steps Parameter (add input here)
226
Parameters give the blocks more information and allow
you to customize their actions. For example, you can use the
say ( ) block to make a sprite say what you want it to.
say I'm the coolest person in the world.
WELL, THEN,
I GUESS IT MUST BE TRUE!
Parentheses ( ) are used to show a parameter,
or input field, when writing out Scratch code.
For example, this block:
move 10 steps
would be written like this: move ( ) steps.
Not all blocks have parameters-
some are just labeled with the
command they perform. when clicked
move 10 steps
This script makes the Scratch Cat
move forward 10 steps then switch
next costume
to its next costume every time
the green flag is clicked.
227
If a script was made up of the event block and a move (1)
step block, when you click the green flag a bunch of times,
the Scratch Cat will walk across the stage. Clicking the green
flag 3 times makes the cat take 3 steps, like this:
Sprites don’t have to walk
when clicked
in straight lines. To make the
Scratch Cat walk in a circle, add
pen down
the turn clockwise (15) degrees
block to the end of the script.
move 10 steps
Then press the green flag 24
times to make the Scratch Cat next costume
walk in a complete circle. Use
turn 15 degrees
the pen down block to draw
the circle.
You press the green flag 24 times because 360
(the number of degrees in a circle) divided by 15
(the number of degrees turned each time) equals 24.
228
To make the Scratch Cat move in a bigger or smaller circle,
the parameters in the move ( ) steps and turn clockwise ( )
degrees blocks can be changed. For example, to make the
circle bigger, you can change the turn clockwise ( ) degrees
input field from 15 to 5. Click the green flag 72 times, and it
will make a bigger circle.
To add pen blocks, open the
The blocks in the Pen
Add Extension menu (bottom-
category can be used to
left corner) and select the
draw shapes on the stage. Pen category. After the Pen
category is added, you’ll see
The pen down block is used
the Pen category blocks at the
to trace a line wherever
end of the Blocks menu.
the sprite moves.
229
Blocks can be inserted into the middle of scripts, not just added to
the end. Scripts are run block by block from the first one at the top to
the last one at the bottom. In order to trace a line wherever the sprite
moves, the “pen down” block must run before the Scratch Cat starts to
move. Insert the block toward the top of the script instead of at the end.
To insert a block within a script:
when clicked
1.
Hold the block between two
pen down
other blocks to get a gap and
shadow to appear.
move 10 steps
2.
Let go of the mouse. next costume
turn 15 degrees
The block will be
inserted here.
Glide
Another way to make sprites move around the stage is the
glide ( ) secs to x: ( ) y: ( ) block found in the Motion category.
Instead of making the sprite walk or move instantly the way
the move ( ) steps block does, the glide ( ) secs to x: ( ) y: ( ) block
assigns a specific amount of time to move the sprite to a
new location. The first parameter tells the sprite how long
to take (in seconds), and the other two parameters tell it
exactly where to go on the stage.
230
HEY, MAN, GOTTA MOVE,
WHAT’S THE RUSH? MOVE, MOVE!
I’M JUST GONNA
GLIDE MY WAY OVER.
= glide for 1 second to
glide 1 secs tox: -50 y: 50
coordinates (−50, 50)
Another movement block, the go to x: ( ) y: ( ) block, can instantly
move the sprite to a specific point on the screen every time
the script runs. By entering 50 in the x parameter field and 50
in the y parameter field, the Scratch Cat will automatically
jump to the location (50, 50).
Glide on over to
the next page
231
| FOR EXAMPLE: | The following script makes the Scratch |
|---|
Cat glide around in a square.
Block #1 runs the script when
| 1 when | clicked | the green flag is clicked. |
| ------ | ------- | -------------------------- |
Block #2 jumps the sprite
| 2 go tox: | 50 y: | 50 |
| --------- | ----- | --- |
to the location (50, 50).
Block #3 erases all previously made
| 3 | erase all | |
| --- | --------- | --- |
pen marks.
Block #4 traces the path of the sprite
| 4 | pen down | |
| --- | -------- | --- |
as it moves.
Blocks move
| 5 glide | 1 secs | tox: -50 y: 50 |
| ------- | ------ | -------------- |
the sprite to all four
corners of a square.
6
| glide | 1 secs | tox: -50 y: -50 |
| ------- | ------ | --------------- |
| 7 glide | 1 secs | tox: 50 y: -50 |
| 8 glide | 1 secs | tox: 50 y: 50 |
232
DEBUGGING STRATEGIES
Programs don’t always run as the programmer intended.
There are strategies to debug (fix problems):
Review scripts one block at a
time. Read each block out loud
and think about what each
block actually does.
Work with small chunks of
code. Break up scripts and run
only small chunks at a time. After running a chunk with
no problems, add another set of blocks and continue to
check for errors.
Comment on scripts explaining what they do and review
the blocks to make sure they do what you are expecting.
Ask a classmate to help by using one of the above
strategies together.
233
BLOCKS AND THEIR FUNCTIONS
Motion
| move | 10 steps | |
| ---- | -------- | --- |
The Motion blocks are used to move a sprite around.
| mmoovvee 1100 | sstteeppss | |
| ------------- | ---------- | --- |
| move | 10 steps | |
| turn | 15 degrees | |
Move ( ) steps: A stack block that moves the sprite forward
| ttuurrnn | 1155 ddeeggrreeeess | |
| -------- | ------------------- | --- |
| turn | 15 degrees | |
| turn | 15 degrees | |
Turn clockwise ( ) degrees: A stack block that turns the sprite clockwise
(to the right)
| ttuurrnn | 1155 ddeeggrreeeess | |
| -------- | ------------------- | --- |
| turn | 15 degrees | |
| go to | random position | |
Turn counterclockwise ( ) degrees: A stack block that turns the sprite
counterclockwise (to the left)
go to random position
go to random position
go to random position
| go to x: | 0 y: 0 | |
| -------- | ------ | --- |
Go to x: ( ) y: ( ): A stack block that jumps the sprite to the location at the
| x-g oantdo yx:-coo0rdinayt:es | 0 | |
| ----------------------------- | --------- | --------------- |
| go to x: | 0 y: 0 | |
| go to x: | 0 y: 0 | |
| glide | 1 secs to | random position |
| glide 1 | secs to | random position |
| glide 1 | secs to | random position |
| glide | 1 secs to | random position |
| glide | 1 secs to | x: 0 y: 0 |
234
| glide 1 | secs to x: | 0 y: 0 |
| ------------------ | ---------------- | ------ |
| glide 1 | secs to x: | 0 y: 0 |
| glide | 1 secs to x: | 0 y: 0 |
| point in | direction 90 | |
| point in direction | 90 | |
| point in direction | 90 | |
| point in direction | 90 | |
| point toward | mouse-pointer | |
| point toward | mouse-pointer | |
| point toward | mouse-pointer | |
| point toward | mouse-pointer | |
| change | x by 10 | |
| change x | by 10 | |
| change x | by 10 | |
| change x | by 10 | |
| set x to | 0 | |
| set x to | 0 | |
| set x to | 0 | |
| set x to | 0 | |
| change | y by 10 | |
| change y | by 10 | |
| change y | by 10 | |
| change y | by 10 | |
| set y to | 0 | |
| set y to | 0 | |
| set y to | 0 | |
| set y to | 0 | |
| if on edge, | bounce | |
| ifon edge, | bounce | |
| if on edge, | bounce | |
| if on edge, | bounce | |
| set rotation | style left-right | |
| set rotation | style left-right | |
| set rotation | style left-right | |
| set rotation | style left-right | |
x position
x position
x position
xyppoossiittiioonn
y position
y position
ydipreocstiitoionn
direction
direction
direction
| mmoovvee 1100 | sstteeppss | |
|---|---|---|
| mmmooovvveee 111000 | sssttteeepppsss | |
| ttuurrnn | 1155 ddeeggrreeeess | |
| tttuuurrrnnn | 111555 dddeeegggrrreeeeeesss | |
| ttuurrnn | 1155 ddeeggrreeeess | |
| tttuuurrrnnn | 111555 dddeeegggrrreeeeeesss |
ggoo ttoo rraannddoomm ppoossiittiioonn
gggooo tttooo rrraaannndddooommm pppooosssiiitttiiiooonnn
| move 10 | steps | |
| ------------------- | ------------------------- | --------------------------------------------- |
| ggoo ttoo xx:: | 00 yy:: 00 | |
| gggooo tttoooxxx::: | 000 yyy::: 000 | |
| turn | 15 degrees | |
| gglliiddee 11 | sseeccss ttoo | rraannddoomm ppoossiittiioonn |
| gggllliiidddeee 111 | ssseeecccsss tttooo | rrraaannndddooommm pppooosssiiitttiiiooonnn |
| turn | 15 degrees | |
| gglliiddee 11 | sseeccss ttoo xx:: | 00 yy:: 00 |
| gggllliiidddeee 111 | ssseeecccsss tttoooxxx::: | 000 yyy::: 000 |
go to random position
| ppooiinntt iinnddiirreeccttiioonn | 9900 | |
| ------------------------------------------------- | ------ | --- |
| pppoooiiinnnttt iiinnndddiiirrreeeccctttiiiooonnn | 999000 | |
Go to ( ): A stack block that jumps the sprite to the mouse pointer or
to a random position on the stage
| go to x: | 0 y: 0 | |
| ---------------------------------- | --------------------------------------- | --- |
| ppooiinntt ttoowwaarrdd | mmoouussee--ppooiinntteerr | |
| pppoooiiinnnttt tttooowwwaaarrrddd | mmmooouuussseee---pppoooiiinnnttteeerrr | |
Point toward ( ): A stack block that points the sprite toward the mouse or
another sprite
| glide 1 | secs to | random position |
| ---------------------------- | --------- | --------------- |
| cchhaannggee xx | bbyy 1100 | |
| ccchhhaaannngggeee xxxbbbyyy | 111000 | |
Change x by ( ): A stack block that moves the sprite along the x-axis
| glide 1 | secs to x: | 0 y: 0 |
| ------------------- | ---------- | ------ |
| sseett xx ttoo | 00 | |
| ssseeettt xxxtttooo | 000 | |
Set x to ( ): A stack block that jumps the sprite to the location along
the x-axis
| point in direction | 90 | |
| ---------------------------- | --------- | --- |
| cchhaannggee yy | bbyy 1100 | |
| ccchhhaaannngggeee yyybbbyyy | 111000 | |
Change y by ( ): A stack block that moves the sprite along the y-axis
| point toward | mouse-pointer | |
| ------------------- | ------------- | --- |
| sseett yy ttoo | 00 | |
| ssseeettt yyytttooo | 000 | |
Set y to ( ): A stack block that jumps the sprite to the location at the y-axis
| change x | by 10 | |
| ---------------------------- | ------------------------------- | --- |
| iiffoonn eeddggee,, | bboouunnccee | |
| iiifffooonnn eeedddgggeee,,, | bbbooouuunnnccceee | |
| set x to | 0 | |
| sseett rroottaattiioonn | ssttyyllee lleefftt--rriigghhtt | |
ssseeettt rrroootttaaatttiiiooonnn ssstttyyyllleee llleeefffttt---rrriiiggghhhttt 235
| change y | by 10 | |
| -------- | ----- | --- |
xx ppoossiittiioonn
xxxpppooosssiiitttiiiooonnn
yy ppoossiittiioonn
syyyetpppoooyssstiiiotttiiiooonnn0
ddiirreeccttiioonn
dddiiirrreeeccctttiiiooonnn
| if on edge, | bounce | |
| ------------ | ---------------- | --- |
| set rotation | style left-right | |
x position
y position
direction
| mm moo ovv vee e | 11 100 0 ss stt tee epp pss | s | |
|---|---|---|---|
| mm oo vv ee | 11 00 ss tt ee pp | ss | |
| tuu urr rnn n | 155 5 dee | egg grr ree eee ess s | |
| tt tt uu rr nn | 11 11 55 dd dd | ee gg rr ee ee ss | |
| tuu urr rnn n | 155 5 dee | egg grr ree eee ess s | |
| tt tt uu rr nn | 11 11 55 dd dd | ee gg rr ee ee ss | |
| gg goo o tt too o | rr raa ann ndd doo omm m pp poo oss | sii itt tii ioo onn n | |
| gg oo tt oo | rr aa nn dd oo mm pp oo | ss ii tt ii oo nn | |
| gg goo o tt too oxx x:: | : 00 0 yy y:: : | 00 0 | |
| gg oo tt oo xx | :: 00 yy :: | 00 | |
| gg gll lii idd dee e | 11 1 ss see ecc css s | tt too o rr raa ann ndd doo omm m | pp poo oss sii itt tii ioo onn n |
| gg ll ii dd ee | 11 ss ee cc ss | tt oo rr aa nn dd oo mm | pp oo ss ii tt ii oo nn |
| gg gll lii idd dee e | 11 1 ss see ecc css s | tt too oxx x:: : 00 0 | yy y:: : 00 0 |
| gg ll ii dd ee | 11 ss ee cc ss | tt oo xx :: 00 | yy :: 00 |
| pp poo oii inn ntt tii inn ndd | dii irr ree ecc ctt tii ioo onn n | 99 900 0 | |
| pp oo ii nn tt ii nn | dd ii rr ee cc tt ii oo nn | 99 00 | |
| poo oii inn ntt ttt too oww | waa arr rdd d moo ouu | uss see e-- -pp poo oii inn ntt tee err r | |
| pp pp oo ii nn tt tt oo | ww aa rr dd mm mm oo | uu ss ee -- pp oo ii nn tt ee rr | |
| chh haa ann ngg gee e | xbb byy y 100 0 | ||
| cc cc hh aa nn gg ee | xx xx bb yy 11 11 00 | ||
| ss see ett txx xtt too o | 00 0 | ||
| ss ee tt xx tt oo | 00 | ||
| cc chh haa ann ngg gee e | yy ybb byy y 11 100 0 | ||
| cc hh aa nn gg ee | yy bb yy 11 00 | ||
| ss see ett tyy ytt too o | 00 0 | ||
| ss ee tt yy tt oo | 00 | ||
| ii iff foo onn nee edd dgg | gee e,, , bb boo ouu unn ncc cee | e | |
| ii ff oo nn ee dd | gg ee ,, bb oo uu nn cc | ee |
If on edge, bounce: A stack block that turns the sprite around when it
hits the edge of the stage
| ss see ett trr roo ott taa att | tii ioo onn nss stt tyy yll lee e | ll lee eff ftt t-- -rr rii igg ghh htt t | |
| ------------------------------ | --------------------------------- | ---------------------------------------- | --- |
| ss ee tt rr oo tt aa | tt ii oo nn ss tt yy ll ee | ll ee ff tt -- rr ii gg hh tt | |
Set rotation style ( ): A stack block that sets the rotation style
| xx xpp poo oss sii itt tii | ioo onn n | | |
| -------------------------- | --------- | --- | --- |
| xx pp oo ss ii tt | ii oo nn | | |
X position: A reporter block that holds the x value of the sprite’s location
| yy ypp poo oss sii itt tii | ioo onn n | | |
| -------------------------- | --------- | --- | --- |
| yy pp oo ss ii tt | ii oo nn | | |
Y position: A reporter block that holds the y value of the sprite’s location
dd dii irr ree ecc ctt tii ioo onn n
dd ii rr ee cc tt ii oo nn
Direction: A reporter block that holds the direction value of the sprite
236
LsoayoksHello!
| | for | | 2 seconds | |
| ---------- | --- | --- | --------- | --- |
| say Hello! | for | 2 | seconds | |
| say Hello! | for | 2 | seconds | |
The Looks blocks are used to change how a sprite looks.
| say Hello! | for | | 2 seconds | |
| ---------- | --- | --- | --------- | --- |
say Hello!
say Hello!
say Hello!
Say ( ) for ( ) seconds: A stack block that makes a speech bubble appear
above the sprite for a set number of seconds
say Hello!
| think Hmm... | | for | 2 | seconds |
| ------------ | --- | --- | --- | ------- |
| think Hmm... | | for | 2 | seconds |
| think Hmm... | | for | 2 | seconds |
Think ( ) for ( ) seconds: A stack block that makes a thought bubble
appear above the sprite for a set number of seconds
| think Hmm... | | for | 2 | seconds |
| ------------ | --- | --- | --- | ------- |
think Hmm...
think Hmm...
think Hmm...
Think ( ): A stack block that makes a permanent thought bubble appear
above the sprite
think Hmm...
| switch costume | to | costume1 | | |
| -------------- | --- | -------- | --- | --- |
| switch costume | to | costume1 | | |
| switch costume | to | costume1 | | |
Switch costume to ( ): A stack block that switches to the named costume
| switch costume | to | costume1 | | |
| -------------- | --- | -------- | --- | --- |
next costume
next costume
next costume
next costume
| switch backdrop | | to backdrop1 | | |
| --------------- | --- | ------------ | --- | --- |
| switch backdrop | | to backdrop1 | | |
| switch backdrop | | to backdrop1 | | |
| switch backdrop | | to backdrop1 | | |
next backdrop
next backdrop
next backdrop 237
next backdrop
| change size | by | 10 | | |
| ------------- | ------- | ------ | --- | --- |
| change size | by | 10 | | |
| change size | by | 10 | | |
| change size | by | 10 | | |
| set size to | 100 | % | | |
| set size to | 100 | % | | |
| set size to | 100 | % | | |
| set size to | 100 | % | | |
| change color | | effect | by | 25 |
| change color | | effect | by | 25 |
| change color | | effect | by | 25 |
| change color | | effect | by | 25 |
| set color | | effect | to | 0 |
| set color | | effect | to | 0 |
| set color | | effect | to | 0 |
| set color | | effect | to | 0 |
| clear graphic | effects | | | |
| clear graphic | effects | | | |
| clear graphic | effects | | | |
| clear graphic | effects | | | |
show
show
show
show
hide
hide
hide
hide
| go to front | | layer | | |
| --------------- | --------------- | ----- | -------- | --- |
| go to front | | layer | | |
| go to front | | layer | | |
| go to front | | layer | | |
| go forward | | | 1 layers | |
| go forward | | | 1 layers | |
| go forward | | | 1 layers | |
| go forward | | | 1 layers | |
| costume | number | | | |
| costume | number | | | |
| costume | number | | | |
| backdrop | number | | | |
| bcaocsktudmroep | nnuummbbeerr | | | |
| backdrop | number | | | |
| size | costume # | | | |
| sbiazcekdrop | nucmobseturme # | | | |
| size | costume # | | | |
| size | costume # | | | |
| ssaayy HHeelllloo!! | ffoorr 22 | sseeccoonnddss | |
|---|---|---|---|
| ssaayy HHeelllloo!! | ffoorr 22 | sseeccoonnddss | |
| ssaayy HHeelllloo!! | ffoorr 22 | sseeccoonnddss | |
| say Hello! | for 2 | seconds |
ssaayy HHeelllloo!!
ssaayy HHeelllloo!!
ssaayy HHeelllloo!!
say Hello!
| tthhiinnkk HHmmmm...... | ffoorr | 22 | sseeccoonnddss |
| ----------------------- | ------ | --- | -------------- |
| tthhiinnkk HHmmmm...... | ffoorr | 22 | sseeccoonnddss |
| tthhiinnkk HHmmmm...... | ffoorr | 22 | sseeccoonnddss |
| think Hmm... | for | 2 | seconds |
tthhiinnkk HHmmmm......
tthhiinnkk HHmmmm......
tthhiinnkk HHmmmm......
think Hmm...
| sswwiittcchhccoossttuummee | ttoo ccoossttuummee11 | | |
| --------------------------- | --------------------- | --- | --- |
| sswwiittcchhccoossttuummee | ttoo ccoossttuummee11 | | |
| sswwiittcchh ccoossttuummee | ttoo ccoossttuummee11 | | |
| switch costume | to costume1 | | |
nneexxtt ccoossttuummee
nneexxttccoossttuummee
nneexxtt ccoossttuummee
next costume
Next costume: A stack block that changes the sprite’s costume to the next
one in the costume list
| sswwiittcchhbbaacckkddrroopp | ttoo bbaacckkddrroopp11 | | |
| ----------------------------- | ----------------------- | --- | --- |
| sswwiittcchhbbaacckkddrroopp | ttoo bbaacckkddrroopp11 | | |
| sswwiittcchh bbaacckkddrroopp | ttoo bbaacckkddrroopp11 | | |
| switch backdrop | to backdrop1 | | |
Switch backdrop to ( ): A stack block that switches to the backdrop that is named
nneexxtt bbaacckkddrroopp
nneexxttbbaacckkddrroopp
nneexxtt bbaacckkddrroopp
next backdrop
Next backdrop: A stack block that changes the backdrop to the next one in
the backdrop list
| cchhaannggee ssiizzee | bbyy 1100 | | |
| ------------------------- | --------- | --- | --- |
| cchhaannggee ssiizzeebbyy | 1100 | | |
| cchhaannggee ssiizzee | bbyy 1100 | | |
| change size | by 10 | | |
Change size by ( ): A stack block that changes the size of the sprite by the
number specified
| sseettssiizzee ttoo | 110000 %% | | |
| -------------------- | --------- | --- | --- |
| sseettssiizzeettoo | 110000 %% | | |
| sseett ssiizzee ttoo | 110000 %% | | |
| set size to | 100 % | | |
Set size to ( )%: A stack block that sets the size of the sprite to a set percentage
| cchhaannggee ccoolloorr | eeffffeecctt | bbyy | 2255 |
| ----------------------- | ---------------- | ---- | ---- |
| cchhaannggee ccoolloorr | eeffffeeccttbbyy | | 2255 |
| cchhaannggee ccoolloorr | eeffffeecctt | bbyy | 2255 |
| change color | effect | by | 25 |
Change ( ) effect by ( ): A stack block that changes an appearance on the
sprite by a set amount
| sseett ccoolloorr | eeffffeecctt | ttoo | 00 |
| ----------------- | ---------------- | ---- | --- |
| sseett ccoolloorr | eeffffeeccttttoo | | 00 |
| sseett ccoolloorr | eeffffeecctt | ttoo | 00 |
| set color | effect | to | 0 |
Set ( ) effect to ( ): A stack block that sets an appearance on the sprite to
a specific setting
| cclleeaarr ggrraapphhiicc | eeffffeeccttss | | |
| ------------------------- | -------------- | --- | --- |
cclleeaarr ggrraapphhiicceeffffeeccttss
| 2cc3llee8aarr ggrraapphhiicc | eeffffeeccttss | | |
| ---------------------------- | -------------- | --- | --- |
| clear graphic | effects | | |
sshhooww
sshhooww
sshhooww
show
hhiiddee
hhiiddee
hhiiddee
hide
| ggoo ttoo ffrroonntt | llaayyeerr | | |
| -------------------- | ------------------ | --------------- | --- |
| ggoottoo ffrroonntt | llaayyeerr | | |
| ggoo ttoo ffrroonntt | llaayyeerr | | |
| go to front | layer | | |
| ggoo ffoorrwwaarrdd | | 11 llaayyeerrss | |
| ggoo ffoorrwwaarrdd | | 11 llaayyeerrss | |
| ggoo ffoorrwwaarrdd | | 11 llaayyeerrss | |
| go forward | | 1 layers | |
| ccoossttuummee | nnuummbbeerr | | |
| ccoossttuummee | nnuummbbeerr | | |
| ccoossttuummee | nnuummbbeerr | | |
| costume | number | | |
| bbaacckkddrroopp | nnuummbbeerr | | |
| bbaacckkddrroopp | nnuummbbeerr | | |
| bbaacckkddrroopp | nnuummbbeerr | | |
| backdrop | number | | |
| ssiizzee | ccoossttuummee ## | | |
| ssiizzee | ccoossttuummee ## | | |
| ssiizzee | ccoossttuummee ## | | |
| size | costume # | | |
| say Hello! | for 2 | seconds | ||
|---|---|---|---|---|
| say Hello! | for 2 | seconds | ||
| say Hello! | for 2 | seconds | ||
| ssaayy HHeelllloo!! | ffoorr 22 | sseeccoonnddss | ||
| say Hello! | for 2 | seconds | ||
| ssaayy HHeelllloo!! | for 2 | seconds |
say Hello!
say Hello!
ssaayy HHeelllloo!!
say Hello!
| tshainyk HHemllmo!... | | for | 2 | seconds |
| ----------------------- | --- | ------ | --- | -------------- |
| think Hmm... | | for | 2 | seconds |
| think Hmm... | | for | 2 | seconds |
| tthhiinnkk HHmmmm...... | | ffoorr | 22 | sseeccoonnddss |
| think Hmm... | | for | 2 | seconds |
| tthhiinnkk HHmmmm...... | | for | 2 | seconds |
think Hmm...
think Hmm...
tthhiinnkk HHmmmm......
think Hmm...
| sthwiintckh cHomstmum...e | | to costume1 | | |
| --------------------------- | --- | --------------------- | --- | --- |
| switch costume | | to costume1 | | |
| switch costume | | to costume1 | | |
| sswwiittcchh ccoossttuummee | | ttoo ccoossttuummee11 | | |
| switch costume | | to costume1 | | |
| nsewxittcchocsotusmtueme | | to costume1 | | |
next costume
next costume
nneexxtt ccoossttuummee
next costume
| snwexittchcobsatcukmderop | | to backdrop1 | | |
| ----------------------------- | --- | ----------------------- | --- | --- |
| switch backdrop | | to backdrop1 | | |
| switch backdrop | | to backdrop1 | | |
| sswwiittcchh bbaacckkddrroopp | | ttoo bbaacckkddrroopp11 | | |
| switch backdrop | | to backdrop1 | | |
| nsewxittcbhabckadckrodprop | | to backdrop1 | | |
next backdrop
next backdrop
nneexxtt bbaacckkddrroopp
next backdrop
| cnheaxntgbeacskidzerobpy | | 10 | | |
| ------------------------- | -------------- | -------------- | ---- | ---- |
| change size | by | 10 | | |
| change size | by | 10 | | |
| cchhaannggee ssiizzee | bbyy | 1100 | | |
| change size | by | 10 | | |
| scehtansigzee stoize | 1b0y0 | 10% | | |
| set size to | 100 | % | | |
| set size to | 100 | % | | |
| sseett ssiizzee ttoo | 110000 | %% | | |
| set size to | 100 | % | | |
| csheatnsgizee | tocolo1r00 | %effect | by | 25 |
| change | color | effect | by | 25 |
| change | color | effect | by | 25 |
| cchhaannggee | ccoolloorr | eeffffeecctt | bbyy | 2255 |
| change | color | effect | by | 25 |
| scehtangecolocrolor | | effeecftfetcot | by0 | 25 |
| set color | | effect | to | 0 |
| set color | | effect | to | 0 |
| sseett ccoolloorr | | eeffffeecctt | ttoo | 00 |
| set color | | effect | to | 0 |
| csleetar grcaoplhoirc | effecetsffect | | to | 0 |
| clear graphic | effects | | | |
| clear graphic | effects | | | |
| cclleeaarr ggrraapphhiicc | eeffffeeccttss | | | |
| clear graphic | effects | | | |
| schleoawr graphic | effects | | | |
show
Clear graphic effects: A stack block that resets the graphic effects to 0
show
sshhooww
show
hsihdoew
hide
Show: A stack block that shows the sprite
hide
hhiiddee
hide
| ghoideto front | | layer | | |
| -------------- | --- | ----- | --- | --- |
| go to front | | layer | | |
Hide: A stack block that hides the sprite
| go to front | | layer | | |
| -------------------- | --- | ---------- | -------- | --- |
| ggoo ttoo ffrroonntt | | llaayyeerr | | |
| go to front | | layer | | |
| ggoo to fofrrownatrd | | layer1 | layers | |
| go forward | | | 1 layers | |
Go to ( ) layer: A stack block that brings the sprite in front of or behind
all other sprites
| go forward | | | 1 layers | |
| ------------------------- | ------- | ----- | --------------- | --- |
| ggoo ffoorrwwaarrdd | | | 11 llaayyeerrss | |
| go forward | | | 1 layers | |
| gc coo s t u m mfe eorwan | nru udm | b e r | | |
| o s t u | m | b e r | 1 layers | |
Go ( ) ( ) layers: A stack block that sends the sprite in front of or back
behind other sprites
| costume | number | | | |
| ---------------------------- | -------------- | ------- | --- | --- |
| ccoossttuummee | nnuummbbeerr | | | |
| b bcaoa c csk ktud dmr o oep | nn nuu umm mbb | bee err | | |
| r p | | r | | |
| costume | number | | | |
Backdrop ( ): A reporter block that holds the number of the backdrop
being shown
| backdrop | number | | | |
| ---------------- | ------------ | --------------- | --- | --- |
| bbaacckkddrroopp | nnuummbbeerr | | | |
| s sbi iaz zce | nuc cmo | obs set u urm e | # | |
| ekdrop | | t m e | # | |
| backdrop | number | | | |
Size: A reporter block that holds the value of the size of the sprite
| size | costume # | | | |
| -------- | ------------------ | --- | --- | --- |
| ssiizzee | ccoossttuummee ## | | | |
| size | costume # | | | |
| size | costume # | | | |
239
Sound
Sound blocks are used to make and modify sounds.
ppllaayyssoouunndd MMeeooww uunnttiillddoonnee
ppllaayyssoouunndd MMeeooww uunnttiillddoonnee
play sound Meow until done
Pplalayy sosuonudn d( ) unMtiel odwone: A sutanctkil bdlooncke that plays the selected sound and
waits to continue the rest of the script until the sound is done playing
ssttaarrttssoouunndd MMeeooww
ssttaarrttssoouunndd MMeeooww
start sound Meow
start sound Meow
Start sound ( ): A stack block that plays the selected sound
ssttooppaallllssoouunnddss
ssttooppaallllssoouunnddss
stop all sounds
Stsotpo palal lslosuonudnsd: sA stack block that stops all sounds in the program
from playing
cchhaannggee ppiittcchh eeffffeeccttbbyy 1100
cchhaannggee ppiittcchh eeffffeeccttbbyy 1100
change pitch effect by 10
change pitch effect by 10
Change ( ) effect by ( ): A stack block that changes the sound effect on
sounds being played by the set amount
sseett ppiittcchh eeffffeeccttttoo 110000
sseett ppiittcchh eeffffeeccttttoo 110000
set pitch effect to 100
set pitch effect to 100
Set ( ) effect to ( ): A stack block that sets the effect on sounds being
plccallyeeaeadrr tssooo uaun nsdedt eenffuffemeccbttsesr
cclleeaarr ssoouunndd eeffffeeccttss
clear sound effects
clear sound effects
Clear sound effects: A stack block that removes all sound effects
cchhaannggee vvoolluummee bbyy --1100
cchhaannggee vvoolluummee bbyy --1100
240
change volume by -10
change volume by -10
sseettvvoolluummee ttoo 110000 %%
sseettvvoolluummee ttoo 110000 %%
set volume to 100 %
set volume to 100 %
vvoolluummee
vvoolluummee
volume
volume
pplalayyssoouunndd MMeeooww uunnttililddoonnee
play sound Meow until done
ssttaarrttssoouunndd MMeeooww
start sound Meow
ssttooppaallllssoouunnddss
stop all sounds
cchhaannggee ppititcchh eefffefeccttbbyy 1100
change pitch effect by 10
sseett ppititcchh eefffefeccttttoo 110000
set pitch effect to 100
ccleleaarrssoouunnddeefffefeccttss
clear sound effects
cchhaannggeevvoolulummeebbyy --1100
change volume by -10
Change volume by ( ): A stack block that changes the volume by the
set amount
sseettvvoolulummeettoo 110000 %%
set volume to 100 %
Set volume to ( ): A stack block that changes the volume to the set percentage
vvoolulummee
volume
Volume: A reporter block that holds the value of current volume level
241
Pen
Blocks in the Pen category are used to draw on the stage.
The Pen category is added as an extension and is not one
of the default categories.
eerraassee aallll
erase all
Erase all: A stack block that removes all pen marks and stamps from the stage
eerraassee aallll
ssttaammpp
stamp
Stamp: A stack block that stamps the image of the sprite to the stage.
ssttaammpp
Stamps cannot be controlled with blocks. Stamps are copies of images
of the sprite printed onto the stage.
ppeenn ddoowwnn
pen down
ppeenn ddoowwnn
Pen down: A stack block that begins to trace the movements of a sprite
ppeenn uupp
with lines
pen up
ppeenn uupp
sseettppeenn ccoolloorrttoo
Pen up: A stack block that stops tracing the movements of a sprite
| set pen color | to | |
| ------------------------ | --------------- | ---- |
| sseett ppeenn ccoolloorr | ttoo | |
| cchhaannggee ppeenn | ccoolloorr bbyy | 1100 |
Set pen color to ( ): A stack block that sets the pen color to the selected color
| change pen | color by | 10 |
| ------------------- | --------------- | ---- |
| cchhaannggee ppeenn | ccoolloorr bbyy | 1100 |
242
| sseettppeenn | ccoolloorr ttoo 5500 | |
| ---------------------- | -------------------- | --- |
| set pen | color to 50 | |
| sseett ppeenn | ccoolloorr ttoo 5500 | |
| cchhaannggee ppeenn | ssiizzee bbyy 11 | |
| change pen | size by 1 | |
| cchhaannggee ppeenn | ssiizzee bbyy 11 | |
| sseettppeenn ssiizzee | ttoo 11 | |
| set pen size | to 1 | |
| sseett ppeenn ssiizzee | ttoo 11 | |
erase all
erase all
erase all
erase all
stamp
stamp
stamp
stamp
pen down
pen down
pen down
pen down
pen up
pen up
pen up
pen up
| set pen color | to | |
| ------------- | -------- | --- |
| set pen color | to | |
| set pen color | to | |
| set pen color | to | |
| change pen | color by | 10 |
| change pen | color by | 10 |
| change pen | color by | 10 |
Change pen color by ( ): A stack block that changes a quality of
| change pen | color by | 10 |
| ---------- | -------- | --- |
the existing pen by the set amount
| set pen | color to 50 | |
| ------- | ----------- | --- |
| set pen | color to 50 | |
| set pen | color to 50 | |
| set pen | color to 50 | |
Set pen color to ( ): A stack block that sets a quality of the pen to
a specific numerical value
| change pen | size by 1 | |
| ---------- | --------- | --- |
| change pen | size by 1 | |
| change pen | size by 1 | |
| change pen | size by 1 | |
Change pen size by ( ): A stack block that
| set pen size | to 1 | |
| ------------ | ---- | --- |
changes the pen size by the set amount
| set pen size | to 1 | |
| ------------ | ---- | --- |
| set pen size | to 1 | |
| set pen size | to 1 | |
Set pen size to ( ): A stack block that sets
the pen size to the set amount
243
IT’S MORE FUN
TO FOLLOW
ALONG ON
YOUR COMPUTER.
244
w
1. What do all hat blocks have in common?
2. What does the pen down block do?
3. What does the following glide 1 secs tox: -50 y: 50
block make a sprite do?
4. How can you tell if a script is running?
5. Select all that are true. Hat blocks can be placed:
A. above other blocks
B. below other blocks
C. inside other blocks
6. Select all that are true. Stack blocks can be placed:
A. above other blocks
B. below other blocks
C. inside other blocks
7. How do you insert a block between two other blocks?
8. Which block should you use to erase all the pen markings
on the stage?
answers 245
21
Chapter
DATA AND
OPERATORS
VARIABLES
Reminder: Boolean
values can only be
Storing information is useful when
either true or false.
you want to reuse it while running
a program. Information can be
stored using variables:
A VARIABLE IS
WHERE A PROGRAM
STORES DATA. THE
Variables: hold one type of value-
DATA IS CALLED
a number, string (text), Boolean, ITS VALUE.
or list
REPORTER BLOCKS
report out, or
deliver, the current value of the variable
they represent. They can store numbers
and words as variable values.
247
A reporter block is placed inside the parameter area of any
other block.
There are reporter blocks in every
blocks category except Events and Control.
A reporter block is shaped
like this:
Variables
You can create a new variable by clicking on “Make a
Variable” in the Variable category of the Blocks menu. After
you make a new variable, a new reporter block with the
variable name appears in the Blocks palette.
There are two ways to change the value of a variable:
1.
set ( ) to ( ) block: used to replace the current value
with a new value
2.
change ( ) by ( ) block: used to add to or subtract
from the current value of the variable
248
FOR EXAMPLE, in a game we can create a variable
called “score” and use the set (score) to (0) stack block to
set the score variable to 0 when the game begins. We can
also use the change (score) by (1) stack block to increase
the score by one point every time the user scores a point
during the game. We can access the value of the score
| | set score | to 0 |
| ---------------------- | --------- | ---- |
| variable with the | set score | to 0 |
| score reporter block. | set score | to 0 |
The reporter block could
be used to display the
| | change score | by 1 |
| ----------------------- | ------------ | ---- |
| score on the stage or | change score | by 1 |
| | change score | by 1 |
tell when a player has
won the game based
| on points scored. | score | |
| ----------------- | ----- | --- |
score
score
249
Built-In Variables
Some reporter blocks have built-in variables that store data.
The values of the variables can be used in programs.
For example, the built-in
go to x: mouse x y: mouse y
variables called mouse x
and mouse y name the
position on the x-axis and y-axis of the user’s mouse cursor on
the stage. These values can be inserted into the parameters
of the go to x: ( ) y: ( ) stack block to make a sprite go to the
user’s mouse location on the stage.
the things users type in
USER INPUT
USER INPUT
Some built-in variables store . We can
ask for users to enter words or numbers by using the
ask ( ) and wait stack-type block found in the Sensing
category. Their answer
is stored in the answer
when clicked
reporter block. We can
ask What's your name? and wait
ask a user to enter their
name, then use the say ( )
say join Hello answer
block to have the sprite
tell the user hello with
their name:
Answer reporter block:
user input stored here
250
The ask ( ) and wait block makes a speech bubble appear
above the sprite and a text box appear at the bottom of the
stage. The script pauses until the user types an answer in
the text box and presses enter on the keyboard.
Lists
In Scratch you can store multiple values in a single place
with LISTS.
List blocks are used to set values and to use the data they
store later in the program.
FOR EXAMPLE,
we could make a high-score list called
“high_score” and use the add ( ) to ( ) stack block to add
the names “Indira,” “Leo,” and “Kemi”:
add Indira to high_score
add Leo to high_score
add Kemi to high_score
251
my list
my list
my list
add thing to my list
my list
add thing to my list
my list
add thing to my list
deletemy1list of my list
add thing to my list
my list
delete 1 of my list
add thing to my list
my list
delete 1 of my list
add thing to my list
delete all of my list
addeldetem th y i1n li g st otfo mmyy l ilsistt
Create a new list by clicking on the Make a List button in the
delete all of my list
deletemy1list of my list
Variable cateadgdory tohfin tghe Btolockmsy mlisetnu. After creating a new list,
delete all of my list
these blocks dweliellt eapmpye1 laisrt ionf thme yB lliosctks palette:
aindsdert ththiningg toat m1y listof my list
ddeelleettee all1of omfy limsty list
my list
aindsdert ththiningg toat m1y listof my list
delete all of my list
delete 1 of my list
ad inde s lde e t r e t athl t l hino ingf g mtoa y t lismt 1y listof my list
dreeplelatece ite1m of1 moyf listmy list with thing
adin desldeetret athltlh inoin gfg mto ayt lismt1 y list of my list
dreeplelatece ite1m of1 moyf listmy list with thing
insert thing at 1 of my list
delete all of my list
di r n ees plee latrec t e i t t h e1i m ng of1 at moy1 f listm o y f lis m t y list with thing
item 1 of my list
delete all of my list
dirne esp leela tre cte itthe 1imng of 1at m o y1f list moyf lismt y listwith thing
diteelemte al1l of ofmym lisyt list
replace item 1 of my list with thing
insert thing at 1 of my list
item 1 of my list
drieteeplemlatec#eaoliltfeomfthimn1gy lisitnof mmyy l ilsistt with thing
insert thing at 1 of my list
item 1 of my list
drieteeplemlatec#eaoliltfeomfthimn1gy lisitnof mmyy l ilsistt with thing
insert thing at 1 of my list
item 1 of my list
rietepmlac#eoitfemthin1g inof mmyy l ilsistt with thing
length of my list
initseemrt 1thingof atmy l1ist of my list
item # of thing in my list
replace item 1 of my list with thing
length of my list
item 1 of my list
insert thing at 1 of my list
item # of thing in my list
rleepnlgatcheoitfemmy l1ist of my list with thing
my list contains things ?
item 1 of my list
item # of thing in my list
rleepnlgatcheoitfemmy l1ist of my list with thing
my list contains things ?
iitteemm # o1f thoifngmyi nlistmy list
rleepnlgatcheoitfemmy l1ist of my list with thing
my list contains things ?
siihtteeommw#liso1tf mthoyif nligstmyi nlistmy list
length of my list
my list contains things ?
siil htte een ommg w th#lisoo 1tff mtmhoy yif nl i lgs is tm t yi nlistmy list
my list contains things ?
sihteomw lis1t moyf listmy list
ilteenmgth# ooff tmhyin lgist in my list
hidemlyis ltist my lisctontains things ?
show list my list
ilteenm mgtyh#
li
oos fft tmhyin clgiosntta in
ins
my
t h
li
i
s
n
t
gs ?
252 hide list my list
show list my list
item # of thing in my list
lenmgtyh liosft my cliosnttains things ?
hide list my list
show list my list
sh l h e id n oemg w t lyh ils i l stios t ft mm m yy y l il sc i l s i tos t nttains things ?
hleidnem gtly his lti o s f t mmy yli sc lito s n t tains things ?
show list my list
hide list my list
my list contains things ?
show list my list
hide list my list
my list contains things ?
show list my list
hide list my list
show list my list
hide list my list
show list my list
hide list my list
hide list my list
hide list my list
Lists start out empty. Use the add ( ) to ( ) blocks to add the
names to the high_score list. The list display (shown on the
stage) will show that the three names have been added to
the high_score list:
The replace item ( ) of ( ) with ( ) stack block is used to
replace items on the list. In the first parameter, type the
number of the index for the item to be replaced. To replace
Kemi with Margaret, type “3” because Kemi is third in the list.
In the last parameter, type “Margaret” because that’s the
new value.
replace item 3 of high_score with Margaret
Other list blocks can be used to delete and insert new
list items.
253
OPERATORS
OPERATORS are used to perform calculations on values. There
are two types of operators blocks:
| | REPORTER | and | BOOLEAN | | |
| --- | -------- | ----- | ------- | --- | --- |
+
The reporter blocks are used to perform mathematical functions
+
on values (such as add, subtract, mu+ltiply, divide, round, and
others). For example, we could make a+ sprite go to a location 50
-
steps above the user’s cursor using an addition reporter block:
-
-
| | | go tox: | mouse x | y: mouse | y + 50 |
| ------------------------ | --- | ------- | ------- | -------- | ------ |
| Boolean-type operators | | | - | | |
*
blocks are used to evaluate
*
statements as true or false.
*
| For example, we can use the ( ) > ( ) block to determine if | | | * | | |
| ------------------------------------------------------------- | --- | --- | --- | --- | --- |
/
a player’s score is greater than 50:
| | | | | score > | 50 |
| --- | --- | --- | --- | ------- | --- |
/
| | + | | / | | |
| --- | --- | --- | --- | --- | --- |
Math Blocks
/
| | | pick | random | 1 to | 10 |
| --- | --- | ---- | ------ | ---- | --- |
+
In the Operators category, there are reporter blocks with
| math operators b+uilt into them:pick | | | random | 1 to | 10 |
| ------------------------------------ | --- | ---- | ------ | ---- | --- |
| | - | pick | random | 1 to | 10 |
| | + | pick | random | 1 to | 10 |
mod
-
mod
-
| | * | | mod | | |
| --- | --- | --- | --- | --- | --- |
mod
-
| | * | round | | | |
| --- | --- | ----- | ------ | --- | --- |
| | * | round | | | |
| | / | round | | | |
| | * | round | | | |
| 254 | | | abs of | | |
/
| | | | abs of | | |
| --- | --- | --- | ------ | --- | --- |
/
| | pick random | 1 to | ab1s0 of | | |
| --- | ----------- | ---- | -------- | --- | --- |
| | / | | abs of | | |
| | pick random | 1 to | 10 | | |
| | pick random | 1 to | 10 | | |
mod
| | pick random | 1 to | 10 | | |
| --- | ----------- | ---- | --- | --- | --- |
mod
mod
round
mod
round
round
| | abs of | | | | |
| --- | ------ | --- | --- | --- | --- |
round
| | abs of | | | | |
| --- | ------ | --- | --- | --- | --- |
| | abs of | | | | |
| | abs of | | | | |
Each block has one or two input fields where you can insert
numbers or variables. The value for each block is the solution
to the math equation shown in the block.
FOR EXAMPLE,
if you wanted to subtract 6 - 2, you
would use the ( ) - ( ) block:
The value of this
block is 4.
6 - 2
WHAT?
You can use math with YOU MEAN I CAN
GET SCRATCH TO DO
variables by inserting
MY MATH HOMEWORK
FOR ME?!
the reporter variables
block into the input field
of a math block.
FOR EXAMPLE,
to find out someone’s age, you could set
a variable, “birth_year,” to the year someone was born (for
example, 2005), and subtract that from the current year:
Name of variable: birth_year
2020 - birth_ year
Value: 2005
255
+
-
+
*
-
/
*
| pick random | 1 to | 10 |
| ----------- | ---- | --- |
/
| > 50 | | |
| ---- | --- | --- |
Boolean Blocks
| | pick random | 1 to 10 |
| --- | ----------- | ------- |
BOOLEAN BLOCKS
evaluate information to be true or
false. The<y h5a0ve statements or math equations inside them
that are either true or false.
50
| = 50 | | |
| ---- | --- | --- |
EXAMPLE:
< 50 The “=” Boolean block looks
at both sides of the equal
| 2 + | 2 = 4 | |
| --- | ----- | --- |
sign and decides if they
true
are the same.
= 50
| 2 + | 1 = 4 | |
| --- | ----- | --- |
The value of the Boolean block is true because 2 + 2 = 4.
false
| | 2 | + 2 = 4 |
| --- | --- | ------- |
If the Boolean block had the equation 2 + 1 = 4, then the value
true
of the block would be false.
| | 2 | + 1 = 4 |
| --------------- | ---------- | ------- |
| join apple | banana | false |
| letter 1 | of apple | |
| | join apple | banana |
| length of apple | | |
256
| | letter 1 | of apple |
| -------------- | --------- | -------- |
| apple contains | a | ? |
| | length of | apple |
mod
| | apple | contains a ? |
| --- | ----- | ------------ |
round
mod
| abs of | | |
| ------ | --- | --- |
round
| | abs | of |
| --- | --- | --- |
+
-
+
| - | | | * | |
| --- | --- | --- | --- | --- |
/
*
| / | | | pick random | 1 to 10 |
| --- | --- | --- | ----------- | ------- |
50
| pick random | 1 | to 10 | | |
| ----------- | --- | ----- | --- | ---- |
| > | 50 | | | < 50 |
Boolean blocks can also be used to compare words. For
example, Marcos = Marcos is true. Marcos = Greg is false.
WE DON’T EVEN
= 50
< 50
LOOK ALIKE.
| | | | Marcos | = Marcos |
| --- | --- | --- | ------ | -------- |
= 50
true
| Marcos | = Marcos | | Marcos | = Greg |
| ------ | -------- | --- | ------ | ------ |
| | true | | | false |
| Marcos | = Greg | | | |
false
| Be careful with spaces! | | | HI, MARCOS. | |
| ---------------------------- | --- | --- | ----------- | --------- |
| Spaces before or after each | | | join apple | banana |
| word compared must match. | | | | OH, HEY, |
MARCOS.
| | | | letter | 1 of apple |
| ---------- | -------- | --- | --------- | ---------- |
| join apple | banana | | | |
| letter 1 | of apple | | length of | apple |
257
| | | | apple | contains a ? |
| --------- | -------- | --- | ----- | ------------ |
| length of | apple | | | |
| apple | contains | a ? | mod | |
round
mod
| | | | abs | of |
| --- | --- | --- | --- | --- |
round
| abs | of | | | |
| --- | --- | --- | --- | --- |
In the Operators category, there are Boolean blocks for
comparison (<, =, >) and logical operations (and, or, not). These
blocks can be combined by nesting them within each other.
FOR EXAMPLE,
you could use the ( ) > ( ) , ( ) < ( ) , and
( ) and ( ) Boolean blocks to see if a variable, score, is greater
than 10 and the timer is less than 200. To do this, insert the
( ) > ( ) and ( ) < ( ) blocks inside the left and right input fields
of a ( ) and ( ) block:
score > 10 and timer < 200
These blocks are nested within a ( ) and ( ) block.
Nesting blocks means putting one or
more blocks inside another block.
In the Sensing category, there are Boolean blocks that check
for specific conditions. If the condition is met, the block’s value
is true; otherwise the value is false.
258
| FOR EXAMPLE, | you could use the key ( ) pressed? |
|---|
Boolean block to sense if the spacebar on the keyboard
is pressed. Or, you could use the touching color ( ) block to
| | | key space pressed? | |
| --- | --- | ------------------ | --- |
check if the sprite is touching a certain color. When these
conditions are met, the blocks will have the value of true.
| key space | pressed? | touching color | ? |
| -------------- | -------- | -------------- | --- |
| touching color | ? | | |
HEY, LET ME KNOW
WHEN THE SPRITE IS
TOUCHING GREEN.
THEN I CAN START
MY HOMEWORK.
259
BLOCKS AND THEIR FUNCTIONS
Variables
The blocks in the Variables category are used to store and
change data as single-value variables or multiple-value lists.
Make a Variable
Make a Variable
Make a Variable
Make a Variable
Make a Variable
my variable
my variable
my variable
my variable
*variablme ynavmarei*a:b Ale reporter block that holds the value of the
named variable
set my variable to 0
set my variable to 0
set my variable to 0
set my variable to 0
set my variable to 0
Set ( ) to ( ): A stack block that sets the value of the selected variable to
a set number, string, or Boolean
change my variable by 1
change my variable by 1
change my variable by 1
change my variable by 1
change my variable by 1
Change ( ) by ( ): A stack block that changes the value of the selected
variable by the set amount
show variable my variable
show variable my variable
show variable my variable
show variable my variable
show variable my variable
Show variable ( ): A stack block that will show the variable value in a little
display window on the stage
hide variable my variable
hide variable my variable
hide variable my variable
hide variable my variable
hide variable my variable
Hide variable ( ): A stack block that will hide the variable value display
window on the stage
260
These Make a List Mb al o c k as Lg si v te the user the ability to change a list of values.
| MM M | aaa k kk kee e e aaa | LLL iii isss t tt | | | | |
| ---- | ----------------------------- | ------------------ | --- | --- | --- | --- |
Make a List
| | my list | | | | | |
| --- | ------------------------ | --- | --- | --- | --- | --- |
| mmm | myyy ylll liii isss sttt | t | | | | |
| | my list | | | | | |
list name: A reporter block that holds the value(s) of the named list
| add | thing | to | my list | | | |
| ----------- | --------------------- | ------ | ------------------------------- | --- | --- | --- |
| addd dddd d | thhh hiii innn nggg g | tooo o | myyy y lll liii isss sttt t | | | |
| aaa | ttt | ttt | mmm | | | |
| add | thing | to | my list | | | |
Add ( ) to ( ): A stack block that adds the set value to the end of the
selected list
| delete | 1 | of | my list | | | |
| -------------------------- | --- | ------ | ------------------------------- | --- | --- | --- |
| deee elll leee ettt teee e | 1 | offf f | myyy y lll liii isss sttt t | | | |
| ddd | 111 | ooo | mmm | | | |
| delete | 1 | of | my list | | | |
Delete ( ) of ( ): A stack block that deletes an item from the selected list
| delete | all of | my list | | | | |
| -------------------------- | --------------------- | ------------------- | ----------- | --- | --- | --- |
| deee elll leee ettt teee e | alll llll looo offf f | myyy y lll liii | isss sttt t | | | |
| ddd | aaa | mmm | | | | |
| delete | all of | my list | | | | |
Delete all of ( ): A stack block that deletes all items from the selected list
| insert | thing | at | 1 of | my list | | |
| ------------------------------ | ----------------------- | ------------ | -------------- | --------------- | --------------------- | --- |
| iii innn nsss seee errr rttt t | ttt thhh hiii innn nggg | g aaa attt t | 111 1 ooo offf | f mmm myyy y | lll liii isss sttt t | |
| insert | thing | at | 1 of | my list | | |
Insert ( ) at ( ) of ( ): A stack block that inserts a value at a location in
a selected list
| replace | item | 1 | of my list | | with thing | |
| ------- | ---- | --- | ---------- | --- | ---------- | --- |
rrr reee eppp plll laaa accc ceee eiii ittt teee emmm m 111 1 ooo offf f mmm myyy y lll liii isss sttt t www wiii ittt thhh h ttt thhh hiii innn nggg g
| replace | item | 1 | of my list | | with thing | |
| ------- | ---- | --- | ---------- | --- | ---------- | --- |
Replace item ( ) of ( ) with ( ): A stack block that replaces the value in
| a location of a selected list item | 1 | of my list | | | | |
| ---------------------------------- | --------------------- | ------------------------------- | -------------------------- | -------------------------- | --- | --- |
| ittt teee emmm m | 1 | offf f myyy | y lll liii isss sttt t | | | |
| iii | 111 | ooo mmm | | | | |
| item | 1 | of my list | | | | |
| item # | of | thing | in my list | | | 261 |
| ittt teee emmm m### #ooo | offf f | thhh hiii innn nggg g | innn n myyy | y lll liii isss sttt t | | |
| iii | | ttt | iii mmm | | | |
| item # | of | thing | in my list | | | |
| length | of | my list | | | | |
| leee ennn nggg gttt thhh hooo | offf f | myyy y lll liii isss sttt t | | | | |
| lll | | mmm | | | | |
| length | of | my list | | | | |
| my list | | contains | | things | ? | |
| myyy y | lll liii isss sttt t | cooo onnn nttt | taaa aiii innn nsss s | thhh hiii innn nggg gsss s | ? | |
| mmm | | ccc | | ttt | ??? | |
| my list | | contains | | things | ? | |
| show list | my list | | | | | |
| sss shhh hooo owww wlll | liii isss sttt t mmm | myyy y lll liii isss sttt t | | | | |
| show list | | my list | | | | |
| hide list | my list | | | | | |
| hhh hiii iddd deee elll liii isss | sttt t mmm myyy | y lll liii isss sttt t | | | | |
| hide list | my list | | | | | |
Make a List
Make a List
Make a List
Mamkye ali sLtist
| my | list | | |
| --- | ---- | --- | --- |
Mmaykel ias tList
Make a List
| my | list | | |
| --------------- | ------------ | ------------ | ---------- |
| my | list | | |
| add mythliinsgt | to | my list | |
| add thing | to my list | | |
| add thing | to my list | | |
| add thing | to my list | | |
| add thing | to my list | | |
| add thing | to my list | | |
| delete | 1 of my list | | |
| delete | 1 of my list | | |
| delete | 1 of my list | | |
| delete | 1 of my list | | |
| delete | 1 of my list | | |
| delete | 1 of my list | | |
| delete all | of my list | | |
| delete all | of my list | | |
| delete all | of my list | | |
| delete all | of my list | | |
| delete all | of my list | | |
| delete all | of my list | | |
| insert | thing at | 1 of my list | |
| insert | thing at | 1 of my list | |
| insert | thing at | 1 of my list | |
| insert | thing at | 1 of my list | |
| insert | thing at | 1 of my list | |
| insert | thing at | 1 of my list | |
| replace | item 1 | of my list | with thing |
| replace | item 1 | of my list | with thing |
| replace | item 1 | of my list | with thing |
| replace | item 1 | of my list | with thing |
| replace | item 1 | of my list | with thing |
| replace | item 1 | of my list | with thing |
| item | 1 of my list | | |
| item | 1 of my list | | |
| item | 1 of my list | | |
Itietemm ( ) of1 ( ): Ao rfepomrtye rli sbtlock that holds the value of an item in the
selietecmted lis1t
of my list
| item | 1 of my list | | |
| --------- | ------------ | ---------- | --- |
| item # | of thing | in my list | |
| item # of | thing in | my list | |
| item # of | thing in | my list | |
| item # of | thing in | my list | |
Itietemm ## ooff ( ) itnh i(n ):g A reinportmery blliosctk that holds the index number value of
| thiet esmet vaolufe inth ain lgist | in | my list | |
| ----------------------------------- | ---------- | ------- | --- |
| length | of my list | | |
| length of | my list | | |
| length of | my list | | |
| length of | my list | | |
| length of | my list | | |
Length of ( ): A reporter block that holds the number of items in
| length of | my list | | |
| ----------------------- | -------- | ------ | --- |
| a selected list my list | contains | things | ? |
| my list | contains | things | ? |
| my list | contains | things | ? |
| my list | contains | things | ? |
| my list | contains | things | ? |
| my list | contains | things | ? |
( ) contains ( )?: A Boolean block asking if a selected list has the set value in
| show list | my list | | |
| --------- | ------- | --- | --- |
it (Is “thing” an item in the list? It‘s true if it is, and false if it is not.)
| show list | my list | | |
| --------- | ------- | --- | --- |
| show list | my list | | |
| show list | my list | | |
| show list | my list | | |
| show list | my list | | |
Shhoiwde lilsits t( ): Am syt alicskt block that will show all the list values in a display
| hide list | my list | | |
| ----------------------------- | ------- | --- | --- |
| window on the stage hide list | my list | | |
| hide list | my list | | |
| hide list | my list | | |
| hide list | my list | | |
Hide list ( ): A stack block that will hide the list values display window on
the stage
262
The previous blocks give the user the ability to change more
than one value in a selected list.
Operators
Blocks in the Operators category are used to control data.
Many of the reporter blocks are
STRING VALUES
mathematical functions (like
Several symbols or
addition, subtraction, multiplication, values that are set
and more). Other blocks are used to in a row
STRING VALUES
| change | | . |
| ------- | --- | --- |
++
++
( ) + ( ): A reporter block that holds the
value of the addition equation
--
--
( ) - ( ): A reporter block that holds the
value of the subtraction equation
**
**
( ) * ( ): A reporter block that holds the
value of the multiplication equation
//
//
( ) / ( ): A reporter block that holds the
value of the division equation
| ppiicckk rraannddoomm | 11 ttoo | 1100 |
| --------------------- | ------- | ---- |
| ppiicckk rraannddoomm | 11 ttoo | 1100 |
263
5500
5500
<< 5500
<< 5500
== 5500
== 5500
aanndd
aanndd
oorr
oorr
nnoott
nnoott
| jjooiinn aappppllee | bbaannaannaa | |
| ---------------------------- | --------------- | ----- |
| jjooiinn aappppllee | bbaannaannaa | |
| lleetttteerr 11 | ooff aappppllee | |
| lleetttteerr 11 | ooff aappppllee | |
| lleennggtthh ooff aappppllee | | |
| lleennggtthh ooff aappppllee | | |
| aappppllee ccoonnttaaiinnss | | aa ?? |
| aappppllee ccoonnttaaiinnss | | aa ?? |
mmoodd
mmoodd
rroouunndd
rroouunndd
| aabbss ooff | | |
| ----------- | --- | --- |
| aabbss ooff | | |
+
+
++
+ +
+
-
-
--
-
-
-
*
*
**
*
*
*
/
/
//
/
/
/
| pick | random | 1 to 10 |
| -------------------- | ------ | ------------ |
| pick random | | 1 to 10 |
| ppiicckkrraannddoomm | | 11 ttoo 1100 |
| pick random | 1 | to 10 |
| pick random | | 1 to 10 |
| pick random | | 1 to 10 |
50
50
Pick rando>>m ( )55 t00o ( ): A reporter block that sets the value to a random
number between the two set values
50
50
50
< 50
< 50
< 50
< 50
( ) > ( ): A Boolean block that evaluates true or false based on whether
the value in the left field is greater than the value in the right field
< 50
< 50
< 50
= 50
= 50
= 50
= 50
( ) = ( ): A Boolean block that evaluates true or false based on whether
the values o=n th5e0 left and right sides of the equal sign are equivalent
= 50
= 50
and
and
and
and
( ) and ( ): A Boolean block that evaluates true or false based on whether
and
both Booleaann dblocks inside are true
and
or
or
or
or
| ( ) or ( ): A Boolean block that evaluates true or false based on whether | or | |
| -------------------------------------------------------------------------- | --- | --- |
or
one or botho rBoolean blocks inside are true
not
not
not
not
not
Notn (o ):t A Boolean block that evaluates to the opposite value of the value
insjiodien thea ppaprlaemeterb, saon athnaat a true parameter evaluates to false and not
| a fj o oaili nsne toa | a tp prp puel e | b a n a n a |
| --------------------- | --------------- | ----------- |
| j | l e | b a n a n a |
| join | apple | banana |
| join | apple | banana |
| join | apple | banana |
| join | apple | banana |
| letter | 1 of | apple |
Jolient t(e ) r( ): A 1reporotfer balopcpkl ethat joins two values into one string
| letter | 1 of | apple |
| --------- | -------- | ----- |
| letter | 1 of | apple |
| letter | 1 of | apple |
| letter | 1 of | apple |
| 26le4tter | 1 of | apple |
| length | of apple | |
| length | of apple | |
| length | of apple | |
| length | of apple | |
| length | of apple | |
| length | of apple | |
| length | of apple | |
| apple | contains | a ? |
| apple | contains | a ? |
| apple | contains | a ? |
| apple | contains | a ? |
| apple | contains | a ? |
| apple | contains | a ? |
| apple | contains | a ? |
mod
mod
mod
mod
mod
mod
mod
round
round
round
round
round
round
round
| abs | of | |
| --- | --- | --- |
| abs | of | |
| abs | of | |
| abs | of | |
| abs | of | |
| abs | of | |
| abs | of | |
+
+
+
+
+
+
-
-
-
-
-
-
*
*
*
*
*
*
/
/
/
/
/
/
pick random 1 to 10
pick random 1 to 10
pick random 1 to 10
pick random 1 to 10
pick random 1 to 10
pick random 1 to 10
50
50
50
50
50
50
< 50
< 50
< 50
< 50
< 50
< 50
= 50
= 50
= 50
= 50
= 50
= 50
and
and
and
and
and
and
or
or
or
or
or
or
not
not
not
not
not
not
join apple banana
join apple banana
join apple banana
join apple banana
join apple banana
join apple banana
letter 1 of apple
letter 1 of apple
letter 1 of apple
letter 1 of apple
Leltetteter r( ) of1 ( ): A orfeporatpepr lbelock that holds the value of the specific letter of
letter 1 of apple
a word
length of apple
length of apple
length of apple
length of apple
length of apple
Lelnegntgh tohf o( )f: A raeppoprlteer block that holds the value of the number of characters
in a string
apple contains a ?
apple contains a ?
apple contains a ?
apple contains a ?
apple contains a ?
apple contains a ?
( ) contains ( )?: A Boolean block that evaluates to true or false based on
whether the value on the left contains the letter on the right
mod
mod
mod
mod
mod
mod
( ) mod ( ): A reporter block that holds the value of the remainder of the
firrsotu vnadlue divided by the second
round
round
round
round
round
Round ( ): A reporter block that rounds the value to the nearest
abs of
whoa aleb b snsumbero o f f
abs of
abs of
abs of
( ) of ( ): A reporter block that holds the value of the selected mathematical
operation using the set number value (For example, you could use this block
to find the square root of a value.)
265
Sensing
Blocks in the Sensing category are used to understand
and store information about how the user interacts with
the program.
| touching | mouse-pointer | ? |
| -------- | ------------- | --- |
| touching | mouse-pointer | ? |
| touching | mouse-pointer | ? |
| touching | mouse-pointer | ? |
Touctohiuncgh (i n)?g: A Bmoooleuasne -bploocikn ttehrat evalu?ates to true or false based on
whether the sprite is touching the mouse-pointer or another sprite
| touching | color ? | |
| -------- | ------- | --- |
| touching | color ? | |
| touching | color ? | |
| touching | color ? | |
| touching | color ? | |
Touching color ( )?: A Boolean block that evaluates to true or false based
on whether the sprite is touching the selected color
| color | is touching | ? |
| ----- | ----------- | --- |
| color | is touching | ? |
| color | is touching | ? |
| color | is touching | ? |
| color | is touching | ? |
Color ( ) is touching ( )?: A Boolean block that evaluates to true or false
based on whether the selected color touches another selected color
| distance | to mouse-pointer | |
| -------- | ---------------- | --- |
| distance | to mouse-pointer | |
| distance | to mouse-pointer | |
| distance | to mouse-pointer | |
| distance | to mouse-pointer | |
Distance to ( ): A reporter block that holds the value of the distance
beatswkeen tWheh sapt'rsit yeo aunrd n tahme em?ouse-apnodintwera iotr another sprite
| ask What's your name? | | and wait |
| --------------------- | --- | -------- |
| ask What's your name? | | and wait |
| ask What's your name? | | and wait |
| ask What's your name? | | and wait |
Asakn (s )w aenrd wait: A stack block that asks the user to answer a question
answer
usainngs wa etrext box and waits for the answer
answer
answer
| key space | pressed? | |
| ------------ | -------- | --- |
| key space | pressed? | |
| key space | pressed? | |
| key space | pressed? | |
| 26k6ey space | pressed? | |
mouse down?
mouse down?
mouse down?
mouse down?
mouse down?
mouse x
mouse x
mouse x
mmoouussee xx
mouse y
mouse y
mouse y
mmoouussee yy
| set drag | mode draggable | |
| -------------- | --------------------------- | --- |
| set drag | mode draggable | |
| set drag | mode draggable | |
| sseettddrraagg | mmooddee ddrraaggggaabblele | |
loudness
loudness
loudness
lloouuddnneessss
timer
timer
timer
ttiimmeerr
reset timer
reset timer
reset timer
rreesseett ttiimmeerr
| backdrop # | of Stage | |
| --------------------- | --------------- | --- |
| backdrop # | of Stage | |
| backdrop # | of Stage | |
| bbaacckkddrroopp ## | ooff SSttaaggee | |
| current | year | |
| current | year | |
| current | year | |
| current | year | |
| current | year | |
| days since | 2000 | |
| days since | 2000 | |
| days days since since | 2000 2000 | |
| days since | 2000 | |
username
username
username
username
username
| touching | mouse-pointer | ? |
|---|---|---|
| touching | mouse-pointer | ? |
| touching | mouse-pointer | ? |
| touching | mouse-pointer | ? |
| touching | mouse-pointer | ? |
| touching | mouse-pointer | ? |
| touching | mouse-pointer | ? |
| touching | color ? | |
| touching | color ? | |
| touching | color ? | |
| touching | color ? | |
| touching | color ? | |
| touching | color ? | |
| touching | color ? | |
| color | is touching | ? |
| color | is touching | ? |
| color | is touching | ? |
| color | is touching | ? |
| color | is touching | ? |
| color | is touching | ? |
| color | is touching | ? |
| distance | to mouse-pointer | |
| distance | to mouse-pointer | |
| distance | to mouse-pointer | |
| distance | to mouse-pointer | |
| distance | to mouse-pointer | |
| distance | to mouse-pointer | |
| distance | to mouse-pointer | |
| ask What's your name? | and wait | |
| ask What's your name? | and wait | |
| ask What's your name? | and wait | |
| ask What's your name? | and wait | |
| ask What's your name? | and wait | |
| ask What's your name? | and wait | |
| ask What's your name? | and wait |
answer
answer
answer
answer
Answer: A reporter block that holds the value of the user-given value
answer
fraomns twheer ask block
answer
| key space | pressed? | |
| --------- | -------- | --- |
| key space | pressed? | |
| key space | pressed? | |
| key space | pressed? | |
| key space | pressed? | |
Key ( ) pressed?: A Boolean block that evaluates to true or false based on
| key space | pressed? | |
| --------- | -------- | --- |
whektehyer thsep saecleected kepyr eiss sperdes?sed
mouse down?
mouse down?
mouse down?
mouse down?
mouse down?
mouse down?
Mouse down?: A Boolean block that evaluates to true or false based on
mouse down?
whether the mouse button is down
mouse x
mouse x
mouse x
mouse x
mouse x
mouse x
Momuoseu sxe: Ax reporter block that holds the value of the mouse location on
thme xo-uasxeisy mouse y
mouse y
mouse y
mouse y
mouse y
mouse y
Mouse y: A reporter block that holds the value of the mouse location on
| set drag | mode draggable | |
| ----------------- | -------------- | --- |
| thsee yt-darxaigs | mode draggable | |
| set drag | mode draggable | |
| set drag | mode draggable | |
| set drag | mode draggable | |
| set drag | mode draggable | |
| set drag | mode draggable | |
loudness
Selot uddranges msode ( ): A stack block that makes a sprite draggable or not
loudness
drlaogugdanbelses by the user
loudness
loudness
loudness
timer
timer
Lotuimdneerss: A reporter block that holds the value of the loudness from an
timer
atttiamcehred microphone
timer
timer
reset timer 267
reset timer
reset timer
reset timer
reset timer
reset timer
reset timer
| backdrop # | of Stage | |
| -------------------- | --------------- | --- |
| backdrop # | of Stage | |
| bbaacckkddrroopp ## | ooff SSttaaggee | |
| backdrop # | of Stage | |
| backdrop # | of Stage | |
| backdrop # | of Stage | |
| current | year | |
| current | year | |
| ccuurrrreenntt | yyeeaarr | |
| current | year | |
| current | year | |
| current | year | |
| days since | 2000 | |
| days since | 2000 | |
| ddaayyss ssiinnccee | 22000000 | |
| days since | 2000 | |
| days since | 2000 | |
| days since | 2000 | |
username
username
uusseerrnnaammee
username
username
username
| ttoouucchhiinngg | mmoouussee--ppooiinntteerr | ?? |
|---|---|---|
| touching | mouse-pointer | ? |
| touching | mouse-pointer | ? |
| touching | mouse-pointer | ? |
| touching | mouse-pointer | ? |
| ttoouucchhiinngg | ccoolloorr ?? | |
| touching | color ? | |
| touching | color ? | |
| touching | color ? | |
| touching | color ? | |
| ccoolloorr | iissttoouucchhiinngg | ?? |
| color | is touching | ? |
| color | is touching | ? |
| color | is touching | ? |
| color | is touching | ? |
| ddiissttaannccee | ttoo mmoouussee--ppooiinntteerr | |
| distance | to mouse-pointer | |
| distance | to mouse-pointer | |
| distance | to mouse-pointer | |
| distance | to mouse-pointer | |
| aasskk WWhhaatt''ss yyoouurr nnaammee?? | aanndd wwaaiitt | |
| ask What's your name? | and wait | |
| ask What's your name? | and wait | |
| ask What's your name? | and wait | |
| ask What's your name? | and wait |
aannsswweerr
answer
answer
aannsswweerr
| kkeeyy ssppaaccee | pprreesssseedd?? | |
| ----------------- | ---------------- | --- |
| key space | pressed? | |
| key space | pressed? | |
| kkeeyy ssppaaccee | pprreesssseedd?? | |
mmoouussee ddoowwnn??
mouse down?
mouse down?
mmoouussee ddoowwnn??
mmoouussee xx
mouse x
mouse x
mouse x
mouse x
mmoouussee yy
mouse y
mmoouussee yy
mouse y
| sseettddrraagg | mmooddee ddrraaggggaabbllee | |
| --------------- | --------------------------- | --- |
| set drag | mode draggable | |
| sseett ddrraagg | mmooddee ddrraaggggaabblele | |
| set drag | mode draggable | |
lloouuddnneessss
loudness
lloouuddnneessss
loudness
ttiimmeerr
ttiimmeerr
timer
timer
Timer: A reporter block that holds the value of the timer that
automatically starts when a program is run
rreesseett ttiimmeerr
rreesseett ttiimmeerr
reset timer
reset timer
Reset timer: A stack block that resets the timer to 0
| bbaacckkddrroopp ## | ooff SSttaaggee | |
| -------------------- | --------------- | --- |
| bbaacckkddrroopp ## | ooff SSttaaggee | |
| backdrop # | of Stage | |
| backdrop # | of Stage | |
( ) of ( ): A reporter block that holds the value of the selected variable for the
selected sprite or stage
| cuu urr rrr ree enn n ttt | yyy eee aaa rrr | |
| ------------------------- | --------------- | --- |
cc
| current | year | |
| ------- | ---- | --- |
| current | year | |
| current | year | |
Current ( ): A reporter block that holds the value of the current year,
month, date, day of week, hour, minute, or second
dddaaayyysss sssiiinnnccceee222000000000
| days since | 2000 | |
| ---------- | ---- | --- |
| days since | 2000 | |
| days since | 2000 | |
Days since 2000: A reporter block that holds the value of the days since
the year 2000
uuussseeerrrnnnaaammmeee
username
username
username
Username: A reporter block that holds the value of the Scratch username
of the Scratcher using the program
268
w
1. Select all that are true. Reporter blocks can be placed:
A. above other blocks
B. below other blocks
C. inside other blocks
2. What can you put inside an input field?
3. What are the two possible values a Boolean block
can have?
4. Explain what reporter blocks do. Why are they useful?
5. What’s the difference between the set ( ) to ( ) and
change ( ) by ( ) blocks?
6. What is the value of the block below?
5 < 7
A. True
C. False
C. 12
D. 35
More questions 269
C
D
22
Chapter
CONTROL BLOCKS
AND
EVENT BLOCKS
CONTROL BLOCKS
Blocks tell other blocks what to do. They tell scripts to run,
pause, repeat, and stop. They are different from event
handler hat blocks because they run based on internal
conditions instead of external events (like the clicking of
the green flag).
YIKES, THAT
One type of control block is BLOCK IS SOO
REPEAT 20
CONTROLLING!
the repeat block, which will
repeat the code inside it a
set number of times.
273
C BLOCKS AND CAP BLOCKS
The Control category also has two other
C BLOCK
types of blocks: the and the
CAP BLOCK
.
C blocks look like the letter C. Other blocks
can be placed in the gap of the C so that the
C block wraps around them. There are two main
types of C blocks: loops and conditionals.
Loops repeat the code placed in the gap of the block.
Conditionals run the code placed in the gap only if their
condition is met.
C blocks are found only in the Control category. There
are different types of loops and conditional statements,
but they all share the same basic C shape.
Cap blocks attach to the bottom of a script and are used to
stop running the script.
PUT A CAP ON IT.
PARTY’S OVER.
Other blocks cannot be
stacked below a cap block.
Cap blocks are found
only in the Control category.
274
EVENT BLOCKS
There are six event handler blocks. The hat-shaped blocks
wait for things like a button press, mouse click, or message
broadcast. When an event handlwerh ernegis1ters tkheyatp rtehsseeird event
happened, they run the script attached to it.
| | | | play sound | Meow | untildone |
| --- | --- | --- | ---------- | ---- | --------- |
Event blocks can be used to make a soundboard that
triggers different sounds to play when different number
keys are pressed.
| when 1 | key pressed | | when 2 | key pressed | |
| ---------- | ----------- | --------- | ---------- | ----------- | --------- |
| | | | when 1 | key pressed | |
| play sound | Meow | untildone | play sound | Chord | untildone |
| | | | play sound | Meow | untildone |
FOR EXAMPLE,
the number keys 1, 2, 3, and 4 are each
assigned a different sound.
| when 2 | key pressed | | when 3 | key pressed | |
| ---------- | ----------- | --------- | ---------- | ----------- | --------- |
| when 1 | key pressed | | when 2 | key pressed | |
| play sound | Chord | untildone | play sound | Cymbal | untildone |
| play sound | Meow | untildone | play sound | Chord | untildone |
| when 3 | key pressed | | when 4 | key pressed | |
| when 2 | key pressed | | when 3 | key pressed | |
| play sound | Cymbal | untildone | play sound | Beat Box | untildone |
| play sound | Chord | untildone | play sound | Cymbal | untildone |
| when 4 | key pressed | | | | |
| when 3 | key pressed | | when 4 | key pressed | |
| play sound | Beat Box | untildone | | | |
| play sound | Cymbal | untildone | play sound | Beat Box | untildone |
275
| when 4 | key pressed | | | | |
| ---------- | ----------- | --------- | --- | --- | --- |
| play sound | Beat Box | untildone | | | |
The when backdrop switches to ( ) block listens for the
backdrop to switch. For example, if you make a game that
switches to a new backdrop for every level, you could set up
an event to listen for the backdrop change and trigger new
opponents to appear.
NOT YET!
The broadcast block is used to send out
messages. When this block is run, it broadcasts a message
out to all of the sprites. Messages are sent without the
user seeing anything, and only the when I receive ( ) block
responds when a message is broadcast.
276
| FOR EXAMPLE, | you could use a broadcast block in a | ||||
|---|---|---|---|---|---|
| if touching | color | ? then |
script that sends a message called “Game Over.” You could
| | | | broadcast | Game Over | |
| --- | --- | --- | --------- | --------- | --- |
then add a when I receive (Game Over) block in another
sprite or the backdrop to have it play a losing sound and
bring up a new backdrop ending the game.
| | | | when Ireceive | Game Over | |
| ------------- | --------- | ------ | --------------- | ------------- | --- |
| if touching | color | ? then | | | |
| | | | startsound | Lose | |
| broadcast | Game Over | | | | |
| | | | switch backdrop | to End Screen | |
| when Ireceive | Game Over | | | | |
| startsound | Lose | | | | |
HEY, GAME OVER.
| switch backdrop | to End Screen | | | | |
| --------------- | ------------- | --- | --- | --- | --- |
YAY! THAT’S
BROADCAST
| | | | F O R M | E . | |
| --- | --- | --- | ------------- | ----- | --- |
| | | | IT’S G O T | IM E. | |
THAT’S NOT
MY MESSAGE.
WHEN I RECEIVE GAME OVER
CLICKED
WHEN
277
LOOPS
All loops are C-type blocks. At the top of the C is where the
type of loop is shown (forever, repeat, or repeat until). The
code that is repeated goes in the “mouth” of the C. Other
blocks can stack above and below loops. You can also place
a loop block inside another loop block, making a nested loop.
Basic Loops
Scratch uses three types of loops:
forever, repeat ( ), and repeat until ( ).
Forever loops will run forever, or until the STILL
WALKING.
program is stopped. You can animate a
character to look like it is walking by
using a forever block. You can tell
the sprite to continually switch to
the next costume. Loops run quickly,
so you can also add the block
wait ( ) secs to slow
down the loop.
type of loop
forever
next costume The curved arrow
is a reminder that,
at the end
wait 0.1 seconds
of the loop, the
loop starts over
and runs again.
278
Repeat ( ) loops tell the sprite exactly how many times you
want it to run when you type in a number in the text box.
FOR EXAMPLE,
you can tell a sprite to change to the next
costume and wait 0.1 seconds only 10 times instead of forever:
repeat 10 NOW JUMP
10 TIMES.
next costume
wait 0.1 seconds
Repeat until ( ) loops will continually repeat until the Boolean
statement inside the loop becomes true.
FOR EXAMPLE,
you can tell a sprite to continually
change to the next
repeat until key space pressed?
costume and wait 0.1
seconds until the user next costume
presses the spacebar
wait 0.1 seconds
on the keyboard:
279
| pen | down |
|---|
Loops can make programs
| | move 100 | steps |
| --- | -------- | ----- |
more efficient. For example,
| if you wanted to draw a square, | turn | 90 degrees |
| -------------------------------- | ---- | ---------- |
you could use a loop to make
| | move 100 | steps |
| --- | -------- | ----- |
your script better. Instead of
| | turn | 90 degrees |
| --- | ---- | ---------- |
using all these blocks to draw
| a square . . . | move 100 | steps |
| --------------- | -------- | ---------- |
| | turn | 90 degrees |
you can look for a pattern of
| | move 100 | steps |
| --- | -------- | ----- |
blocks that repeat themselves,
| put the repeated blocks inside | turn | 90 degrees |
| -------------------------------- | ---- | ---------- |
a loop, and input the number
of times you want the script
| | pen | down |
| --- | --- | ---- |
to run.
repeat 4
Nested Loops
| Nested loops are loops inserted | move 100 | steps |
| --------------------------------- | -------- | ----- |
within a loop. Nested loops
| | turn | 90 degrees |
| --- | ---- | ---------- |
are very helpful for repeating
SUBROUTINES
within a task.
They can help make scripts shorter
and more efficient.
SUBROUTINE
A unit of code that
Subroutines are often used
performs a specific task
in games and to make
and is used as part of a
| interesting art. | larger program | |
| ----------------- | -------------- | --- |
280
| FOR EXAMPLE, | in a game where the user tries to |
|---|
catch a falling apple, a forever loop can be used to keep
the game
| going forever, | when clicked | | |
| --------------- | ------------ | --- | --- |
restarting the
forever
apple at the top
| of the screen | go tox: pickrandom | -220 to 220 | y: 130 |
| -------------- | ------------------ | ----------- | ------ |
every time it
repeat 25
reaches the
| bottom. A | change yby | -10 | |
| ----------- | ---------- | --- | --- |
repeat ( ) loop
| | wait 0.1 | seconds | |
| --- | -------- | ------- | --- |
can be used to
animate the
falling apple:
WE’RE NESTING DOLLS!
REPEAT 10 WE’RE
NESTED
REPEAT 20
LOOPS!
REPEAT 5
281
You can also use nested loops to make Spirograph-type
art. The repeat (6) loop in a script draws a hexagon. The
Scratch Cat uses the pen tool to draw a hexagon beneath it
as it moves along the path set by the repeat (6) loop.
when clicked
pen down
repeat 6
move 70 steps
turn 60 degrees
when clicked
Then nest that loop inside the
pen down
repeat (72) loop to redraw the
repeat 72
hexagon 72 times.
repeat 6
move 70 steps
turn 60 degrees
You can rotate to the right
change pen color by 10
by 5 degrees each time and
turn 5 degrees
change the color of each
new hexagon as well.
282
Here’s what the script run to completion looks like. There are
72 hexagons of different colors, each rotated 5 degrees to
the right.
CONDITIONAL STATEMENTS
Scratch has two types of conditional blocks:
If ( ) then
If ( ) then else
Conditional statements use C-type blocks and are found only
in the Control category of the Blocks menu.
283
Basic Conditional Statements
Basic conditional statements use only one Boolean block as
a condition and aren’t nested.
FOR EXAMPLE,
you can use a basic conditional statement
to allow a player to choose a path in a game:
when clicked
ask Which door do you choose? Door 1 or Door 2? and wait
if answer = Door 1 then
say You walk through Door 1 and receive a magic wand.
else
say You walk through Door 2 and receive an enchanted hat.
1.
The script asks the user which door they choose.
2.
A conditional block compares the user’s answer to
the term “Door 1” in a Boolean ( ) = ( ) block.
3.
If the user answers “Door 1,” then the block inside
the first “mouth” will run.
4.
If the user does not answer with “Door 1,” then the
code below “else” in the second “mouth” will run.
284
Compound and Nested
Conditional Statements
Conditional blocks can nest inside
each other just like loop blocks.
Nested conditionals are built
IF
E
N
H
ELSE W
when you put one conditional
inside of another conditional.
In a single “if else” statement, there are two consequences.
CONSEQUENCE #2
CONSEQUENCE #1
E
T S
R L
U A
E F
IF
285
Conditional blocks can be nested inside each other just like
loop blocks. Nested conditional blocks create a more complex
branching system, where many different results can occur.
CONSEQUENCE #4
CONSEQUENCE #3
E
T R A L S
U E F
CONSEQUENCE #2
IF
T R U L S E
E A
F
CONSEQUENCE #1
IF
E
T R U A L S
E F
IF
Multiple nested conditional blocks can be used to create a
choose-your-own-adventure game. Start with the question
asking which door the user chooses and the first condition
with the Boolean block that is True if the user answers “Door 1.”
In the “else” (or FALSE) second “mouth” of the conditional
block, we can add another condition checking for “Door 2.”
Continue to nest conditional blocks to add to the number of
possible results.
286
| FOR EXAMPLE, | this game has four possible outcomes: |
|---|
when clicked
ask Which door do you choose? Door 1 or Door 2? and wait
outcome #1
| if answer | = Door 1 | then |
| --------- | -------- | ---- |
say You walk through Door 1 and receive a magic wand.
else
outcome #2
| if answer | = Door 2 | then |
| --------------------------------------------------------- | -------- | ---- |
| say You walk through Door 2 and receive an enchanted hat. | | |
else
outcome #3
| if answer | = Door 3 | then |
| --------- | -------- | ---- |
say You walk through the secret Door 3 and receive an extra life.
else
say You have not chosen to walk through a door. You grow tired.
outcome #4
Conditional statements can be combined to save space and
simplify the script. The and Boolean block is used to combine
two Boolean blocks.
287
| FOR EXAMPLE, | you can add a bonus round to a game |
|---|
by combining two conditions to entering the bonus round:
having a score of over 100 points and playing on the
“hard” difficulty level.
| | | if score | > | 100 then | |
| --- | --- | -------- | --- | -------- | --- |
Nested, these
| conditions look | | if difficulty | | = hard | then |
| ---------------- | --- | ------------- | --- | ------ | ---- |
like this:
| | | broadcast | StartBonusRound | | |
| --- | --- | --------- | --------------- | --- | --- |
You can simplify
the script by
combining the
Boolean statements from both conditions
with an “and” operators block:
| if score | > | 100 and | difficulty | = hard | then |
| ------------------------- | --- | ------- | ---------- | ------ | ---- |
| broadcast StartBonusRound | | | | | |
AND is True if both conditions are true;
OR is True if one or both conditions are true;
NOT turns True statements False and False statements True.
288
BLOCKS AND THEIR FUNCTIONS
Events
Blocks in the Events category are used to run scripts based
on events that happen while the program is running.
| when | clicked | |
| ---- | ------- | --- |
| when | clicked | |
| when | clicked | |
| when | clicked | |
When green flag clicked: A hat block that runs the attached script when
the green flag is clicked
| when space | key pressed | |
| ---------- | ----------- | --- |
| when space | key pressed | |
| when space | key pressed | |
| when space | key pressed | |
When ( ) key pressed: A hat block that runs the attached script when
the selected key is pressed
| when this | sprite clicked | |
| --------- | -------------- | --- |
| when this | sprite clicked | |
| when this | sprite clicked | |
| when this | sprite clicked | |
When this sprite clicked: A hat block that runs the attached script when
the sprite is clicked
| when backdrop | switches | to backdrop1 |
| ------------- | -------- | ------------ |
| when backdrop | switches | to backdrop1 |
| when backdrop | switches | to backdrop1 |
| when backdrop | switches | to backdrop1 |
When backdrop switches to ( ): A hat block that runs the attached script
when the backdrop switches to the selected backdrop
| when loudness | > | 10 |
| ------------- | --- | --- |
| when loudness | > | 10 |
| when loudness | > | 10 |
| when loudness | > | 10 |
289
| when I receive | message1 | |
| -------------- | -------- | -------- |
| when I receive | message1 | |
| when I receive | message1 | |
| when I receive | message1 | |
| broadcast | message1 | |
| broadcast | message1 | |
| broadcast | message1 | |
| broadcast | message1 | |
| broadcast | message1 | and wait |
| broadcast | message1 | and wait |
| broadcast | message1 | and wait |
| broadcast | message1 | and wait |
| when | clicked | |
|---|---|---|
| when | clicked | |
| when | clicked | |
| when | clicked | |
| when | space key | pressed |
| when | space key | pressed |
| when space | key pressed | |
| when space | key pressed | |
| when this | sprite clicked | |
| when this | sprite clicked | |
| when this | sprite clicked | |
| when this | sprite clicked | |
| when backdrop | switches | to backdrop1 |
| when backdrop | switches | to backdrop1 |
| when backdrop | switches | to backdrop1 |
| when backdrop | switches | to backdrop1 |
| when | loudness > | 10 |
| when | loudness > | 10 |
| when loudness | > | 10 |
| when loudness | > | 10 |
When ( ) > ( ): A hat block that runs the attached script when the video or
timer value goes above the set amount
| when I receive | message1 | |
| -------------- | ---------------- | --- |
| when I | receive message1 | |
| when I receive | message1 | |
| when I receive | message1 | |
When I receive ( ): A hat block that runs the attached script when
the selected message is broadcast
| broadcast | message1 | |
| --------- | -------- | --- |
| broadcast | message1 | |
| broadcast | message1 | |
| broadcast | message1 | |
Broadcast ( ): A stack block that sends out the selected message to
every sprite
| broadcast | message1 | and wait |
| --------- | -------- | -------- |
| broadcast | message1 | and wait |
| broadcast | message1 | and wait |
| broadcast | message1 | and wait |
Broadcast ( ) and wait: A stack block that sends out the selected message
to every sprite and waits to move on to the next block
290
Control
The Control category contains blocks that are used to control
the flow of a program.
| wait 1 | seconds | |
| ------ | ------- | --- |
| wait 1 | seconds | |
| wait 1 | seconds | |
Wait ( ) seconds: A stack block that pauses the script for the set number
of seconds
| wait 1 | seconds | |
| --------- | ------- | --- |
| repeat 10 | | |
| repeat 10 | | |
| repeat 10 | | |
| repeat 10 | | |
Repeat ( ): A C block that repeats the code inside the set number of times
forever
forever
forever
forever
| if | then | |
| --- | ---- | --- |
| if | then | |
Forever: A C block that repeats the code inside forever or until the
| if | then | |
| --- | ---- | --- |
program is stopped
| if | then | |
| --- | ---- | --- |
| if | then | |
| if | then | |
| if | then | |
Ief ls( )e then: A C block that, if the Boolean statement is true, runs the blocks
else
| if | then | 291 |
| --- | ---- | --- |
else
else
wait until
wait until
wait until
repeat wait until until
repeat until
repeat until
repeat until
stop all
stop all
stop all
| when I start | as a clone | |
| ------------ | ---------- | --- |
stop all
| when I start | as a clone | |
| ------------ | ---------- | --- |
| when I start | as a clone | |
| create clone | of myself | |
| when I start | as a clone | |
| create clone | of myself | |
| create clone | of myself | |
| delete this | clone | |
| create clone | of myself | |
| delete this | clone | |
| delete this | clone | |
| delete this | clone | |
wait 1 seconds
wait 1 seconds
wait 1 seconds
wait 1 seconds
repeat 10
repeat 10
repeat 10
repeat 10
forever
forever
forever
forever
if then
if then
if then
if then
if then
if then
if then
else
if then
else
else
else
If ( ) then else: A C block that, if the Boolean statement is true, runs the
blocks in the first part and otherwise runs the blocks in the second part
wait until
wait until
wait until
wait until
Wait until ( ): A stack block that pauses the script until the Boolean
condition is true
repeat until
repeat until
repeat until
repeat until
Repeat until ( ): A C block that repeats the blocks inside until the Boolean
cosntdoitpion isa ltlrue
stop all
stop all
stop all
when I start as a clone
when I start as a clone
Stwohpe (n ): IAs ctaarpt balsocak tchloant estops the selected script(s)
when I start as a clone
ccrreeaatteecclolonneeooff mmysyesleflf
create clone of myself
create clone of myself
292
ddeelleettee tthhisiscclolonnee
delete this clone
delete this clone
wait 1 seconds
wait 1 seconds
wait 1 seconds
repeat 10
repeat 10
repeat 10
forever
forever
forever
if then
if then
if then
if then
if then
eiflse then
else
else
wait until
wait until
wait until
repeat until
repeat until
repeat until
Clone Blocks: Cloning a sprite is when you make copies of
it. Cloning is useful when you need several copies of the
stop all
same sprite on the stage at once.
stop all
stop all
when I start as a clone
when I start as a clone
when I start as a clone
When I start as a clone: A hat block that runs attached script when
a clone is made
create clone of myself
create clone of myself
create clone of myself
Create clone of ( ): A stack block that creates a clone of the
selected sprite
delete this clone
delete this clone
delete this clone
Delete this clone: A cap block that deletes the clone
CONTROL
293
w
1. What are loops? Why are they useful?
2. loops are loops within other loops.
3. How is a repeat ( ) loop different from a forever loop?
4. What does the broadcast ( ) block do? After a program
broadcasts a message, will the message appear on
the stage? when clicked
when clicked
move 10 steps
5. Which kind of C block would you use to make a loop that
move 10 steps
keeps repeating until the ubsroeard ceaastrnsm e10ss apgoei1nts?
broadcast message1
6. In the code below, what will be said first after the program
is started?
when Ireceive message1
when Ireceive message1
say Oh, hello there!
say Oh, hello there!
when clicked
broadcast message2
broadcast message2
move 10 steps
broadcast message1
when Ireceive message2
when Ireceive message2
say Hi!
say Hi!
294when Ireceive message1
say Oh, hello there!
broadcast message2
when Ireceive message2
say Hi!
What does the following event block do? Why are event
blocks important?
| when this | sprite clicked | |
| --------- | -------------- | --- |
A loop is a chunk of code that is repeated.
They are useful because they can make your
code more efficient and easier to write because you
won’t have to copy and paste the same script over
and over again.
Cap blocks end a script; blocks cannot be connected
below a cap block.
23
Chapter
REUSING
SCRIPTS
MAKE YOUR OWN BLOCK
You can turn a repeating part of a script into a new block.
PROCEDURE BLOCK
This new block is called a . You
can make a new procedure block with its own commands
and behavior.
Procedures are named chunks of code that you can
use over and over again. In Scratch, you can make
a procedure block by making a new define ( ) block.
define
()
299
When you make a new
procedure, you click
“Make a Block,” and
select the type of
block you would like
to make. Then you
define the procedure
with a definition
hat-type block (called define ( )) and snap your code
blocks to it. After you make a new procedure block, a new
PROCEDURE CALL STACK BLOCK with the same name as the
new procedure is added to the My Blocks category of the
CALL THE PROCEDURE
Blocks menu. You can (run it) with
the new block name stack block, which is named the same
as the new procedure.
For example,you can use a procedure block to make a game
where the object is to catch good items and avoid bad ones.
The game can give points to the player for catching good
items and take points away when they catch bad items. Your
game can have four items, each worth different points:
crystal = 10 points
For the game, minus (-)
potion = 5 points
means that points
bat = -10 points will be taken away.
lightning = -5 points
300
You can make a procedure block called hit and use the
define ( ) hat-type block to define the procedure and add
a parameter called “points”:
procedure block
define hit points parameter
definition
block
change size by points
change score by points
The change size by (points) block will change the size of the
sprite.
The parameter value is entered into the parameter field in
the procedure call stack block.
FOR EXAMPLE,
you can enter “10” into the hit ( ) procedure
call stack block to give the “points”
parameter the value of 10: hit 10
301
If you run the hit (10) stack block with a value of 10 in
the points parameter, then the sprite will get bigger on
the stage by 10 percent. It will also add 10 points to your
score variable.
You can add
conditional forever
statements that
if touching Crystal ? then
check to see if
the sprite touches hit 10
each of the four
items and add
if touching Potion ? then
a hit procedure
stack block to hit 5
each conditional
statement.
if touching Bat ? then
hit -10
You can enter
a different
parameter value
if touching Lightening ? then
in each of the hit
hit -5
procedure stack
blocks based on the
value of the item
touched:
302
CLONING
CLONING
a sprite is when
you make copies of it. The
clone blocks are found in
the Control category of the
Blocks menu.
CLONING MACHINE
FOR EXAMPLE,
if you wanted to make it rain on the
stage, instead of creating hundreds of individual raindrop
sprites, you could clone a single raindrop sprite hundreds
of times.
To do this, you need
two scripts. SCRIPT 1
Script 1 creates the clones when clicked
of a sprite. You can use a
forever
loop to continually make
new clones forever:
create clone of myself
wait 0.1 seconds
303
If you run Script 1 alone, it will create a bunch of clones of the
sprite, but the clones won’t be programmed to do anything.
Script 2 programs the sprites to act like raindrops, falling
from the sky and disappearing when they hit the ground.
SCRIPT 2
| when I start | as a clone | | |
| ------------- | ---------- | ----------- | ------ |
| go to x: pick | random | -240 to 240 | y: 170 |
| repeat until | touching | edge ? | |
| change y | by -5 | | |
| delete this | clone | | |
The when I start as a clone event hat block runs for
each new clone that is created.
The pick random ( ) to ( ) block makes each raindrop start
in a random location on the x-axis. You can also make
the raindrop start at the top of the screen by setting
the location on the y-axis. To set the location, add the
go to x: ( ) y: ( ) block and add the pick random ( ) to ( )
block and all the parameters.
304
Add a repeat until loop to animate the sprite to fall until
it hits the ground.
Use the change y by ( ) block and a -5 as its parameter
value to make the raindrop move down the screen
toward the ground.
Delete this clone will delete the clone once it reaches
the ground.
There is a 300-clone limit to Scratch programs. Once you
reach the maximum on the screen, no new clones will be
made. But because you are deleting your clones once they
hit the ground you won’t exceed the 300-clone limit.
OMG, IT’S
RAINING
CATS!
305
BLOCKS AND THEIR FUNCTIONS
My Blocks
The My Blocks category is different from all the other
categories because you can create an unlimited number of
new blocks. For each new block you create, a new define ( )
hat block and new block name stack block appear in the
category menu.
Note: Blocks in the My Blocks category appear only after
a new procedure block has been made.
define procedure number or text boolean
define procedure number or text boolean
Define ( ): A hat block that defines a new procedure block along with
sppreoccifeideudr eparameters
procedure
New block name: A stack block that is used to call, or run,
the corresponding procedure. When this block is run, the code
underneath the corresponding define ( ) block is run.
306
w
1. If you want to make a bunch of copies of a sprite,
which blocks should you use?
2. How is making a new block different from just using
a loop block?
3. Why should you delete a clone when you are done
using it?
4. Why is making a new block better than copying and
pasting code?
5. When a new clone is made, what script does it run?
ARE YOU
A CLONE?
answers 307
Unit
7
g
Pro ramming
in Python
330099
24
Chapter
GETTING
STARTED
WITH PYTHON
INTRODUCING PYTHON
Python is one of the most widely
used and easy-to-learn
I’M SO
programming languages,
POPULAR.
which makes it popular for
beginners. It can be used for
many types of projects, ranging
from designing websites to
examining large amounts of data.
310
Python comes with many useful built-in FUNCTIONS, or tools,
including:
math functions like basic operations, square root,
and choosing a random number
options for drawing graphics
user-friendly menus and buttons
IDLE
INTEGRATED DEVELOPMENT
Python code is written in an
ENVIRONMENT PROGRAM (IDE)
like IDLE (Integrated
Development and Learning Environment), the one that comes
with Python when you install it.
INTEGRATED
The program IDLE is
DEVELOPMENT
installed along with
ENVIRONMENT (IDE)
Python. It has two
A program that programmers use
different windows: the
to type out and edit code and to
SHELL WINDOW and create Python programs
EDITOR WINDOW
the .
311
The shell window is the window that
The >>> symbol is
appears when you open IDLE. On the called the prompt.
screen you’ll see “>>>,” which shows
you where to start typing.
To run code in the shell window,
OUTPUT
type it in next to the prompt and The result of the code;
OUTPUT what you see after
press enter. The of
the code has run
your code will appear on the line
below. Or, if your code doesn’t run
properly, an error message will appear.
FOR EXAMPLE,
you can type in the code print(“Hello,
World!”) and your output will be “Hello, World!” like this:
The shell window is great for
running small pieces of code, >>> TYPE HERE.
but isn‘t good for writing
whole programs because you
can’t save your work.
Shell window
312
The editor window is for writing out whole programs
that are saved as files. The editor window starts out as
a completely blank, untitled file. Python files end in .py,
and you can save them anywhere on your computer.
An example of a Python file name would be
firstproject.py.
This is a file extension.
It names the format of a file.
When working in Python:
name the file something that’s
related to your project
YOU CAN
save it somewhere that CALL ME .PY
you’ll remember
save your work often
Saving Files tip
Create a new folder called “Python_Projects”
inside your “My Documents” folder to save all your
Python project files. This will help you stay organized
and help you remember where to find your work.
313
CODE
Instructions must be written using
The rules for
code. All parts of the code have to be
writing programs
written according to the rules of the are called syntax.
Python programming language.
Python comes with built-in functions
PARAMETER
(a section of code that performs a
VALUE
specific task). One of the functions
The text put within
is called print. The print function the parentheses of
a function
print( ) will display in the shell
window the text that you add as
PARAMETER VALUE
a .
Hello, Python
“Hello, World!” is one of the most basic programs you can
write in any computer language. The “Hello, World!” program
can be made in Python by calling the print function and
typing “Hello, World!” as the parameter value like this:
Parentheses
print("Hello, World!")
Function name Parameter value
314
The print( ) function tells
To call a function means
the computer to display the to instruct the computer to
use that specific tool.
parameter value.
Be very careful when
MY COMPUTER
typing out your code. If
IS PICKIER ABOUT
words are misspelled, SPELLING THAN
your program may not MY ENGLISH
TEACHER!
run properly. Do not add
extra spaces or symbols.
Capitalization also BOOP!
matters. For example,
entering “Print” instead
of “print” won’t work.
KEEPING
BULLETIN BOARD
ORGANIZED
COMMENTS
in
your code are little
notes to yourself and
other programmers.
Comments aren’t run
as part of the program
but can be read by
315
anyone reading your code. They act like sticky notes
and can help organize your thoughts. Comments can be
reminders, explanations about the code, and questions.
To make a comment in Python, use either the # symbol for
a one-line comment or three quotation marks-single (‘’’) or
double (“ ” ”)-for multiple lines.
'''Multiline # only at the beginning, but
multiline comments open and
comment can take
close with the quotation marks.
many rows.'''
I’M HELPFUL
AS WELL AS
POPULAR.
316
Helpful Colors
Both the shell and editor windows automatically change the
color of your text to help you read your code.
Purple is for built-in functions. For example, print( ) is a
built-in function.
Orange is for key words that have special meaning, like “if”
and “True.”
Green is for all text that appears in quotation marks.
Double or single quotation marks can be used as long as
they match-in other words, don’t start with single quotation
marks and end with double quotation marks.
Blue is for the output text from when the program runs.
Red is for error messages that appear when the program
doesn’t run properly.
Black is for all the rest of the text in the program.
317
w
1. Why do the shell and editor windows automatically
change the color of your text as you type?
2. What does the IDLE program do? Why is it helpful?
3. Write in the blank which window you should use for each
of the following:
A. You want to write a large program in Python.
B. You want to save your work.
C. You want to quickly run a small piece of code.
4. Match each color in the left column with what it
represents in IDLE in the right column.
A. Output Purple
B. Text inside quotation marks Orange
C. Key words Green
D. Error Blue
E. Built-in function Red
318
The colors help you, the programmer, read your
code more easily.
print( )
I WEAR
COLOR WELL,
DON'T YOU
THINK?
322
25
Chapter
VARIABLES
IN PYTHON
VARIABLES
are used to store information. Storing
information is useful when you want to reuse that
information many times or use it at different times while
running a program. They save you from entering the same
block of code over and over.
DATA TYPE
DATA TYPES The kind of value
In Python, the basic
the data is
that can be stored by variables
include:
strings
integers
lists
Boolean values
323
LIST
Variables can store values
An ordered sequence
STRING
(content or data), like a ,
of values
LIST BOOLEAN
number, , or .
USING VARIABLES
STRING
A data type that
To assign a value to a variable,
represents text
use this format:
BOOLEAN
identifier = value
A data type that
represents either
The IDENTIFIER is the name of “True” or “False”
the variable.
FOR EXAMPLE,
in a game where the player gets three
lives, you could name a variable “lives” and assign it a
value of 3:
VALUE
In Python, the “=” sign
means is assigned to.
lives = 3
Read “lives = 3” as
“3 is assigned to lives.”
IDENTIFIER
324
After creating the variable and assigning it the value of 3,
you can reuse the lives variable throughout the program.
Rules for Naming Python Variables
When coming up with the variable identifier, or name, you
must follow these rules:
GOOD
* Use numbers, uppercase letters, lowercase
letters, and underscores (_).
* Start the identifier with a letter.
* Keep your identifier short and simple, and
have it describe the variable it’s used for.
Score
Mice_4
s
e
v
li
325
When coming up with the variable identifier, or name, do not
do this:
BAD
* Include spaces or symbols (like -, /, #, and @).
* Use key words that already mean something else
in Python (like “print”).
* Use the capital letters O or I or a lowercase l,
because those can get confusing-a capital O
looks like the number 0.
* Start your variable with a number or symbol.
Key words in Python (not allowed as identifier names):
| and | def | finally | in | pass | while |
| -------- | ------- | -------- | ------- | ------- | ------ |
| as | del | for | is | print | with |
| assert | elif | from | lambda | raise | yield |
| break | else | global | not | return | |
| class | except | if | or | try | |
| continue | exec | import | | | |
326
When naming a variable, try to describe what it is.
FOR EXAMPLE,
while you could name a variable for
storing the number of lives a player has “j,” you might
forget what “j” means after you add in many more
variables.
But if you name the variable “lives,” you’ll remember that
the variable stores the number of lives for the player.
Also, keep variable names short; longer names lead to more
typos and wasted time typing out the extra characters.
FOR EXAMPLE,
although a variable called the_number_of_
lives_the_player_has_left describes the data it stores, it’s
better to shorten it to just lives.
327
Formatting Variable Names
NAMING CONVENTIONS
Programmers often use to make
their code easier to read. A naming convention is a format
for naming things like variables. Python will run correctly no
matter which naming convention you pick. However, it’s best
to stick to one way in order to make your code easier to read.
Common naming conventions include:
DESCRIPTION EXAMPLES
Single lowercase letter x
Single uppercase letter X
All lowercase treasure
Lowercase and underscores x_position
All uppercase CAPTAIN
For Python, many people prefer to use
lowercase_and_underscores when naming variables.
328
Uppercase and SHIP_NAME
underscores
Capitalized words JollyRoger
(Pascal case)
Capitalize the first letter
of every word in the name.
Mixed case (camel case) buriedTreasure
Capitalize only the
first letter of the Case
second word in a
camel
name. Think of it like
a camel’s hump in the
middle of the name.
Capitalized words with Polly_Want_A _Cracker
underscores
329
w
1. Declare a variable called winning_number and give it
a value of 1001.
2. Which of these are NOT allowed as Python variable
names?
A. @UserName
B. handle
C. Num_posts
D. FriendCount
3. In Python, what does the “=” symbol mean?
4. Write a two-word variable using camel case.
5. Why might it be a good idea to stick with the same
naming convention in a program you’re making?
330
winning_number = 1001
26
Chapter
STRINGS
STRINGS
are a group of sequenced characters within
either single or double quotation marks. You use strings to
show messages or text on-screen
in your program. When Python
sees quotation marks around text,
it reads it as a string.
FOR EXAMPLE:
These are all strings because they are
surrounded by quotation marks:
“Game Over”
‘time: 1:06’
“Lives left:”
“Welcome LOL. Can I tell you a joke?”
333
Don’t mix single and double quotes.
For example, ‘board game night”
doesn’t work.
To assign a variable the value of
a string, name the variable, add
the assignment operator (the equal
symbol), then add the string in
quotation marks.
FOR EXAMPLE,
for a joke-telling program, we can name
a variable “welcome,” add the assignment operator, then add
the value “Welcome LOL. Can I tell you a joke?” like this:
welcome = "Welcome LOL. Can I tell you a joke?"
USING THE PRINT FUNCTION
WITH A STRING
To display the value of a variable using the print function:
First assign the variable a value.
welcome = "Welcome LOL. Can I tell you a joke?"
334
Then type the name of the variable inside the
parentheses of the print function.
VARIABLE
print(welcome)
FUNCTION
This will make the shell window display the welcome
message:
Welcome LOL. Can I tell you a joke?
IMPORTANT: if you used quotation marks around the
variable name, like in the code below, the result would be
different.
welcome = "Welcome LOL. Can I tell you a joke?"
print("welcome")
quotation marks included
This will make the shell window print: welcome
When you put text in quotation marks, Python recognizes it
as a string instead of a variable. So instead of looking up
the variable value, it just prints out the word “welcome” as
a string.
335
Displaying Text on Multiple Lines
To make a string automatically display on multiple lines, use
three single quotation marks (''') and type the text on new
lines the way you want it to appear.
FOR EXAMPLE:
joke = '''I was wondering why the ball
kept getting bigger and bigger,
and then it hit me.'''
print(joke)
This will print:
SMACK!
I was wondering why the ball
kept getting bigger and bigger,
and then it hit me.
The output will have the same
line breaks that were entered
in the string.
336
Changing the Value of
a String Variable
You can change the value of a variable by adding another
line of code that assigns the variable a new value in the
same way you assigned the original value.
FOR EXAMPLE,
to replace “LOL” with “meh”:
reaction = "lol"
Value of reaction: lol
reaction = "meh"
Value of reaction: meh
“meh” replaces “lol” as the value of reaction.
print(reaction)
New value of reaction: meh
This will print: meh
The example prints “meh”
because that was the latest
value of reaction.
Once the value of a variable is changed,
the old value is gone for good.
337
FORMATTING STRINGS
You can style strings so that they include the same type of
punctuation and presentation as regular typed text.
Quotation Marks
All strings have quotation marks around them. So if you
want to put quotation marks inside your string, you’ll need
ESCAPE
to the interior quotation marks by placing a
backslash () before each of them.
FOR EXAMPLE:
BACKSLASH
tornado_joke = "What do you get if you say "tornado"\ ten
times backward and forward? . . . A real tongue twister!"
print(tornado_joke)
This will print:
What do you get if you say "tornado" ten times backward and
forward? . . . A real tongue twister!
When you escape a character, you are telling
Python to treat that character as part of
the string instead of as a special character.
338
EXCEPTION! If you use single quotation marks at the
beginning and end of your string, then you can use double
quotation marks as part of your string without needing to
escape them. (Or, if you use double at the beginning and end,
you can use single as part of the string.)
FOR EXAMPLE,
you could assign the tornado_joke variable
the following value and get the same result as before:
tornado_joke = 'What do you get if you say "tornado" ten
times backward and forward? . . . A real tongue twister!'
But you should still know how to escape characters in case
you need to use both single and double quotation marks or
other characters in a string.
“”
339
Line Breaks
To print on a new line, use an escaped “n” like this:
print("\n")
FOR EXAMPLE,
you could break up the lines of a joke to
emphasize the punch line:
print("I had a talking parrot.\n But it didn't say it was
hungry,\n\n so it died.")
This will print:
HEY,
NOT COOL!
I had a talking parrot. But it
didn't say it was hungry,
so it died.
340
HELLO,
HELLO!
OPERATORS OPERATOR?
OPERATORS
are symbols
that represent actions that
manipulate values. Many
operators come from math.
* is a mathematical operator that represents multiplying.
+ is a mathematical operator that represents adding.
You can use operators with strings as well as numbers.
FOR EXAMPLE,
to say “Hello!” 3 times, you could use:
print("Hello!" * 3) MULTIPLICATION
OPERATOR
“Hello!” * 3 means “Hello!” × 3
This would print: Hello!Hello!Hello!
To add space between each “Hello!” add a space at the end
of the string:
SPACE
print("Hello! " * 3 )
This will print: Hello! Hello! Hello!
341
String Addition
Operators can also be used to add strings together to make
a sentence.
FOR EXAMPLE:
SPACE
part1 = "Why did the chicken cross the road? "
part2 = "To get to the other side."
print(part1 + part2)
This will display: Why did the chicken cross the road? To get
to the other side.
Another way to add strings together is by creating a new
variable that is the sum of two other variables.
part1 = "Why did the chicken cross the road? "
part2 = "To get to the other side."
whole_joke = part1 + part2
This would assign the variable
whole_joke the value of
Why did the chicken cross
the road? To get to the other side.
342
Addition operators can combine both variables and strings
into a new string variable value like this:
animal = "alligator"
joke = "Why did the " + animal + " cross the road?"
print(joke)
The spaces around the + signs make the code easier to read.
Because they aren’t part of a string, the computer ignores
them. You could also correctly type this:
"Why did the "+animal+" cross the road?"
and it would display the same thing:
Why did the alligator cross the road?
Variables are helpful because they
can change values, making programs
more flexible.
343
Sometimes you want a user to input information.
The input( ) function displays the text you add between the
parentheses and waits for the user to type something.
input("add your text here")
The shell window will display “add your text here”
and wait for the user to type something in the window
and press enter.
You can save the information the user types in the shell
window to a variable.
To do this, before the input function, type the name of
the variable you want to use and also add the assignment
operator:
Variable that will store the user’s answer
variable = input("add your text here")
Your text or question to display for the user
344
FOR EXAMPLE,
you can use the input( ) function to ask
the user to give a new value to the “animal” variable from
the joke example:
animal = input("What's your favorite animal? ")
joke = "Why did the " + animal + " cross the road?"
print(joke)
The program will ask the question, then wait for
the user to type in their answer and press ENTER.
What's your favorite animal? Alligator
After the user inputs their answer, this line will print
using the information stored in the “animal” variable.
Why did the Alligator cross the road?
This part is the answer the user entered.
String Functions
Python has built-in functions that change strings in
helpful ways. There are functions to capitalize the first
letter of a word or sentence, join multiple strings into
345
a single string, convert a string to all lowercase letters,
replace part of a string, format a string into a nicer-looking
output, and more.
STRING FUNCTIONS
help change data into a more
usable format. For example, if you ask a user what their
favorite animal is and they type “ALLIGATOR” in all caps,
the lower( ) function can change all the capital letters to
lowercase.
Use string functions by using this format:
variable.function( )
If you have a variable called “animal” and you want to
make sure the value is in lowercase, use the lower( ) function
on the name variable:
FUNCTION
animal.lower( )
VARIABLE
You can use the string functions along with a string almost
anywhere in a program.
346
Examples of different placements of the lower( ) function:
animal = input("What's your favorite animal? ").lower( )
print("Why did the " + animal + " cross the road?")
animal = input("What's your favorite animal? ")
animal = animal.lower( )
print("Why did the " + animal + " cross the road?")
animal = input("What's your favorite animal? ")
print("Why did the " + animal.lower( ) + " cross the road?")
All three examples will print the same output:
Why did the alligator cross the road?
Some of the Most common String Functions
capitalize( ): Changes the first letter to uppercase and the rest
to lowercase
lower( ): Changes all uppercase letters to lowercase
swapcase( ): C hanges capital letters to lowercase and lowercase
letters to capital
upper( ): Converts lowercase letters to uppercase
347
w
1. Which of these is NOT a string:
A. “string cheese”
B. ‘shoelace’
C. “She said, \“keep pulling the thread\””
D. 5 + 9
2. What will the Python code below print?
art = "painting"
print("my favorite kind of art is: " + art)
3. Explain how to make a string print on multiple lines.
4. If you want to ask a user their favorite color, what
would be a good function to use? How would you
write it?
5. What does it mean to escape a quotation mark in
a string?
6. What code could you add as input to the print function
below so that it prints on a new line?
print( )
348
D
27
Chapter
NUMBERS AS
VARIABLES
Variables can also be numbers. When assigning a number
value to a variable, DO NOT surround the number with
quotation marks.
number = 5 A number can be a string
if you surround it with
string = "five"
quotation marks. But you
string = "5" can’t do math with a string.
CALCULATIONS WITH
NUMBER VARIABLES
In Python, you can use numbers to
calculate math problems. For example, you
can create a homework helper program
where Python does the calculations.
351
You can make two number
Remember to assign the
variables, add them together,
values of “num1” and “num2”
and then print the sum before you use them in a
calculation for “sum.” You
like this:
can’t use variables until after
you assign them values.
num1 = 4
num2 = 5
sum = num1 + num2
print(sum)
This will print: 9
NUMBER TYPES
Python uses different types of numbers. Two of those types
INTEGERS FLOATS
are and .
Integers
In Python, integers are positive or negative whole numbers
that don’t use a decimal place.
You can create a variable called “num1” and assign it an
integer value of 3:
A whole number
num1 = 3
352
String variables, even if they have whole numbers inside
them, aren’t recognized by Python as integers.
FOR EXAMPLE,
when you add two strings together, they
are combined as one string:
Quotation marks around the
num1 = "4"
number means it’s a string.
num2 = "3"
sum = num1 + num2
print(sum)
This will print 43, which is the string 4 and the string 3
combined into a single string.
Sometimes it‘s necessary to convert a variable to an integer
data type.
FOR EXAMPLE,
if you ask a user to enter a number using
the input( ) function, Python stores their answer as a string.
width = input("Enter the rectangle's width. ")
height = input("Enter the rectangle's height. ")
In the program above, if the user entered 5 and 8, the numbers
would be stored as strings-"5" and "8"-and not as integers.
353
Convert the user’s answers from strings to integers using the
int( ) function. You can then perform calculations with them.
Multiply the length and width of
Width and height
a rectangle to find the area like this: start out as strings.
width = input("Enter the rectangle's width. ")
height = input("Enter the rectangle's height. ")
width = int(width)
height = int(height) Width and height are
reassigned as integers.
print(width*height)
The number values for width and height can now be
used in calculations, such as finding the area.
Floats
Floats (or floating point numbers) are numbers that have a
decimal point.
FOR EXAMPLE,
the values to these variables are floats:
num1 = 3.3
FLOATS
num2 = 6.0
num3 = 2.9564576
354
To convert a variable value from an integer or string to
a float, use the float( ) function like this:
num1 starts out as an integer.
num1 = 6
num1 is reassigned as a float.
num1 = float(num1)
Calculations with a float keep the digits
sum = num1 + 3.3 to the right of the decimal point.
Will display: 9.3 (the sum of 6.0 + 3.3)
print(sum)
Number Conversion
int( ): Converts a value to an integer. Useful for converting a
user’s input string into an integer to do math.
float( ): Converts a value to a floating point number (number
with a decimal point). Useful when you are using values that
are not whole numbers.
355
MATHEMATICAL EXPRESSIONS
Numbers and math are used in programming to represent
the location of a character in a game, calculate dates,
set timers, display colors,
calculate scores, and EXPRESSION
more. VALUES and A combination of values and
OPERATORS operators that can be evaluated
combine
to a single value. For example,
EXPRESSIONS
to make .
2 + 3 is an expression that
evaluates to (or equals) 5.
EXAMPLES OF
OPERATOR
EXPRESSIONS:
2 + 3
4 * 3 VALUES
3 / 4 * 5 - 5 / 2
(7 * 3) - (5 - 7) / (4 + 5)
Variables can also hold
VALUE
number values and be used in
A piece of information.
mathematical expressions. For
In mathematical
example, if a variable called “x” expressions, values
are numbers.
holds the value of 4, it can be
used in an expression:
x + 6 B ecause x holds the value 4, this expression
evaluates to 10.
356
There are seven common math operators:
| NAME | SYMBOL | EXAMPLE | |
| -------- | ------ | ------- | --- |
| addition | + | 5 + 2 | |
-
| subtraction | | 5 - 2 | |
| ----------- | --- | ----- | --- |
The remainder
portion of
| multiplication | * | 5 * 2 | a quotient. |
| -------------- | --- | ----- | ------------- |
For example,
5 ÷ 2 = 2 with
| | / | | a remainder, or |
| -------- | --- | ----- | ---------------- |
| division | | 5 / 2 | |
modulus, of 1.
| modulus | % | 5 % 2 | |
| ------- | --- | ----- | --- |
**
| exponent | | 5 ** 2 | |
| --------------- | --- | ------ | --- |
| floor division | // | 5 // 2 | |
Divides two numbers and ignores the remainder.
For example, 5 ÷ 2 = 2 (the remainder, 1, is ignored).
The symbols “x” and “÷” are not used in Python.
357
ORDER OF OPERATIONS
ORDER OF OPERATIONS
Use the
ORDER OF
when solving equations:
OPERATIONS
A set of rules for
1. Solve any parts of the equation that deciding the order
that operations
are inside brackets or parentheses.
will be evaluated
If there is more than one set of
parentheses, solve the innermost
equation first.
Parentheses can be nested. This means that there can be one set
of parentheses inside another set, like this: ((2 + 18) * 5) /10.
The innermost equation is 2 + 18 and should be solved first.
2.
Calculate exponents, absolute value, and square roots
from left to right.
3.
Solve all the multiplication and division from left to right.
4.
Complete the addition and subtraction from left to right.
To remember the order of operations, think “Please Excuse
My Dear Aunt Sally,” or PEMDAS (Parentheses, Exponents,
Multiplication, Division, Addition, Subtraction). But be careful,
because PEMDAS isn’t foolproof. For example, you should do
subtraction before addition if you’re calculating from left to
right—and the same goes for division and multiplication.
358
| FOR EXAMPLE, to evaluate the expression 2 * (6 - 3): | ||
|---|---|---|
| First, solve the equation in parentheses: | 2 * (6 - 3) | |
| 6 - 3 = 3 | 2 * (3) | |
| Then, multiply to get your answer: | 2 * 3 = 6 |
If you have the same expression
| without the parentheses . . . | | 2 * 6 - 3 |
| ----------------------------------- | ---------- | ---------- |
| First, multiply: | 2 * 6 = 12 | 12 - 3 |
| Then, subtract to get your answer: | | 12 - 3 = 9 |
Even though they contain the same numbers, the two
equations have different answers because of the order
of operations. Python will always follow the order of
operations when it returns a value.
Printing Mathematical Expressions
If an expression is inside the print function, then Python
will print the value of the expression to the shell window.
FOR EXAMPLE:
| print(5 * 3) This will print: 15 | | |
| --------------------------------- | --- | --- |
359
w
1. In Python, what does the ** operator do?
2. To find the remainder of a division, you would use the
operator.
3. What will each expression return?
A. 5 // 4
B. 3 * (5 + 2) - 6
C. 2 * 5
D. 4 / 2
E. 6 % 2
F. 6 / 3 + (2 - 1) + 2 * 3
4. Write out the code to print the answer to 5 times 2.
5. In the correct order of operations, which comes first:
exponents or addition?
6. What is an expression?
360
Will the following program print an integer or a float
number?
d = 4.2
t = 3
speed = d / t
print(speed)
** is used as the exponent operator.
The problem is “human_years” is assigned the value of 3
after it is used in the first line (human_years * 7).
28
Chapter
LISTS AND
BOOLEAN
EXPRESSIONS
LISTS
LIST
A is a variable that stores multiple values. This is
useful when you have several pieces of information that
you want to store in one place. Lists can store all types of
values including numbers, strings, and other lists.
In Python, lists are formatted using square brackets (and
sometimes quotation marks), with a comma between each item.
For example, we can make a list called “fruits” and assign it
the values apples, bananas, grapes, oranges, and pears:
LIST NAME LIST ITEMS
fruits = ['apples', 'bananas', 'grapes', 'oranges', 'pears']
365
Note: Each item is separated by a comma, but make sure
the commas are on the outside of the quotation marks
so they are not included as part of the string.
Think of a list as a row of boxes, where each box holds a
value. Every box on the list gets a number, starting with 0.
INDEX
This number is called the .
list
0 1 2 3 4
index
The index is used to find or change specific values, or items,
within the list. In the fruit example, apples is located at
index location 0, and the index location of pears is 4.
A specific item in a list is located using the format list[#],
where “list” is the name of the list and “#” is the index
location of the item.
So, fruits[0] is apples and fruits[4] is pears.
366
To display the second item of the fruits list, use the print
function, enter “fruits” as the name of the list, and “1” for
the index location of the item:
print(fruits[1])
Because the index starts at 0, the
second item has an index of 1.
This will print: bananas
You can also print out a section of the list by naming the
range of indexes to print, like this:
ending index
print(fruits[1:4])
starting index
This will print: ['bananas', 'grapes', 'oranges']
The ending index (4: pears)
is not included.
367
When you use print( ) to display more than one item in a list,
the output will include the brackets and quotation marks.
That’s because you’re printing a list, not just items in a list.
There are lots of different ways
The last item isn’t listed—
to update a list.
only the items up to the
ending index position are
included in the list.
You can replace an item in a list
after the list has been created.
To replace a value of an item within a list,
1. reference (name) the index location
2. reassign the value
To replace grapes with kiwi: ['apples', 'bananas',
'grapes', 'oranges', 'pears']
The index location of grapes is 2. You can replace grapes
by assigning index 2 of the fruits list to kiwi:
GET OUTTA
fruits[2] = "kiwi"
HERE!
The list is now: ['apples',
'bananas', 'kiwi', 'oranges',
'pears']
368
To add an item to the end of Append means
a list, use the append( ) function. “to add”
If the list of fruits was a shopping list, the append( )
function would add items to the end of it.
You can add “cherries” to the list by applying the append
function to the fruits list like this:
fruits.append("cherries")
Commas are
added automatically
The list is now: ['apples', 'bananas',
when you add new
'kiwi', 'oranges', 'pears', 'cherries'] items to a list.
To insert an item between two other
values in a list, use the insert( ) function.
Inside the parentheses, tell the
function where to insert the new
value and what the value should be.
Add “peaches” to index location 2 of the fruits list using
the insert( ) function like this:
fruits.insert(2, "peaches")
new item index location value to insert
369
The list is now: ['apples', 'bananas', 'peaches', 'kiwi',
'oranges', 'pears', 'cherries']
To remove an item from a list, use the remove( ) function.
Inside the parentheses, tell the function which item you
want removed by entering the value (the name of the
item, not the index number):
MAKE
ROOM!
fruits.remove("kiwi")
I'M
OUT!
The list is now:
['apples', 'bananas',
'peaches', 'oranges',
'pears', 'cherries']
To sort a list,
• use either the sort( ) function, which will put the
list in numerical or alphabetical order (A-Z), or
• use the reverse( ) function, which will put the
list in reverse order.
ME
FIRST
fruits.sort( )
orders the list to: ['apples', 'bananas',
'cherries', 'oranges', 'peaches', 'pears']
370
GIMME
fruits.reverse( )
THAT!
orders the list to:
['pears', 'peaches',
'oranges', 'cherries',
'bananas', 'apples']
To get the number of items in a list, use the len( ) function:
fruits = ['pears', 'peaches', 'oranges', 'cherries',
'bananas', 'apples']
fruit_length = len(fruits) (Put the name of the list
inside the parentheses.)
print(fruit_length)
prints: 6
To add one list to the end of another list, use the “+”
operator:
fruits = ['apples', 'bananas', 'kiwi']
vegetables = ['carrots', 'peas', 'onions']
produce = fruits + vegetables
Give the new variable (the
print(produce) combined list) a name.
prints: ['apples', 'bananas', 'kiwi', 'carrots', 'peas',
'onions']
371
List functions
list[#]: References a specific item in a list, where “#” is the
index number of the item and “list” is the name of the list
append(“item”): Adds an item to the end of a list
insert(#, “item”): Inserts an item in a specific index
location in a list
remove(“item”): Removes an item from a list
sort( ): Sorts a list by numerical or alphabetical order
reverse( ): Sorts a list by reverse order
len( ): Provides the number of items found in a list
Lists Within Lists
A list can be set within another list. The second list is
INNER LIST
called the . You can use this list to show a
subcategory-a more specialized group. The format for
making a list within a list is a second set of brackets
within the first:
Outer list Outer list continued
list = ["A", "B", "C", ["D1", "D2", "D3"], "E"]
Inner list, stored in fourth item location of outer list
372
FOR EXAMPLE,
to list favorite apples within the list of
favorite fruits:
1.
enter the opening bracket
2.
add the types of apples in quotation marks,
and end with a closing bracket
3. continue with the rest of the list
Outer list Inner list
fruits = ["bananas", ["Gala", "Empire", "McIntosh", "Golden
Delicious"], "kiwi", "oranges", "pears"]
Inner list Outer list continued
The list of apples is stored as the second item of the fruits list.
To print just the favorite apples (the inner list) from the list
of favorite fruits, use the print function with the second
item (index location 1) of the favorite fruits list:
2nd item
print(fruits[1])
list name
prints: ["Gala", "Empire", "McIntosh", "Golden Delicious"]
373
You can print a single apple name by using the index location
1 to reference the list of apples and then adding the index
location of the specific apple.
For example, to print “McIntosh” off the inner list of apples,
use this code:
specific apple
print(fruits[1][2])
list of apples
prints: McIntosh
BOOLEAN EXPRESSIONS
In programming, it’s very common to want to know if
something is true or false. For example, in a game we want
to know if the game is over, or if it is still going, or if a user
got a question right or wrong.
Python automatically detects a Boolean-type variable when
the value is set to “True” or “False,” (a Boolean expression).
When you’re setting a variable to “True” or “False,” make
sure you capitalize the T in True and the F in False. For
example: my_value = True.
Boolean variables are like light
switches. There are only two options:
on or off (True or False).
374
When you assign a Boolean expression to a variable, Python
will set the value to “True” or “False” depending on whether
the Boolean expression is true or false. For example:
Assigns “height” the value of 58.
height = 58
meet_limit = height > 50
Assigns “meet_limit” the value
print(meet_limit) of “height > 50.” This means
that a height of greater than
50 will be considered true.
This will print: True
The expression is True because the given height is 58, and
58 > 50, which means that meet_limit is true.
Number variables store the answer
to a calculation and not the mathematical expression.
Boolean variables are similar because they store
“True” or “False” as the answer to a comparison
expression instead of the comparison itself.
This example shows assigning the variable of test1 to the
Boolean expression 2 is equal to 4, which is false.
test1 = 2 == 4
print(test1)
This will print: False
375
| COMPARISON OPERATORS | evaluate information to be |
|---|
true or false. They compare two values to each other.
Comparison operators are:
| SYMBOL | MEANING | SYMBOL | MEANING |
| ------ | --------------- | --------------------------- | ------- |
| == | is equal to | > is greater than | |
| != | is not equal to | <= is less than or equal to | |
| | | >= is greater than or | |
| < | is less than | | |
equal to
Examples of expressions that evaluate to True:
| EXPRESSION | | MEANING | VALUE |
| ---------- | ------------------------------- | ------- | ----- |
| 2 == 2 | 2 is equal to 2 | | True |
| 2 != 3 | 2 is not equal to 3 | | True |
| 2 < 3 | 2 is less than 3 | | True |
| 4 > 3 | 4 is greater than 3 | | True |
| 2 <= 2 | 2 is less than or equal to 2 | | True |
| 5 >= 3 | 5 is greater than or equal to 3 | | True |
376
Examples of expressions that evaluate to False:
| EXPRESSION | MEANING | VALUE |
| ---------- | ------------------------------- | ----- |
| 2 == 5 | 2 is equal to 5 | False |
| 2 != 2 | 2 is not equal to 2 | False |
| 3 < 3 | 3 is less than 3 | False |
| 2 > 3 | 2 is greater than 3 | False |
| 5 <= 3 | 5 is less than or equal to 3 | False |
| 2 >= 3 | 2 is greater than or equal to 3 | False |
377
w
1. are used to store multiple values.
2. What function should you use to add an item to the end
of a list?
3. How can you replace the second item in the list “cars”
with “Porsche”?
4. What function should you use to add an item between
two existing items in a list?
5. How do you store a list within a list?
6. Explain what the sort( ) function does.
7. Write the code that would print “bananas” given the list
below:
fruits = ["apples", "bananas", "kiwi", "oranges", "pears"]
378
Lists
29
Chapter
FOR LOOPS
Python uses different types of
LOOP
LOOPS
to perform different
Code used to repeat a
actions. FOR LOOPS repeat code sequence of commands
a specified number of times.
FORMATTING FOR LOOPS
The for loop follows a very specific format; even the
number of spaces you use on certain lines is important.
Steps for Creating a For Loop:
STEP 1: Enter the key word “for.” For loops always start with
“for” to show that the following code is a for loop.
COUNTER VARIABLE
STEP 2: Name the . This variable’s
value increases each time the loop repeats. For example, if
you are using a for loop that loops 10 times, starting with
0 and increasing by 1 each time the loop starts over, the
counter variable will represent 0 in the first run, then 1 in
381
the next run, then 2, then 3, and so on, increasing by 1 each
time the loop starts over.
You can name the counter variable anything you want. Many
programmers name their counter variable “i” out of tradition.
STEP 3: Add the key word “in” to show that you are about
to specify how many times the loop should repeat.
STEP 4: Set the number of times the loop should repeat.
Use the range( ) function to do this. The range function will
count from zero up to, but not including, the number listed in
the function’s parentheses.
RUN
THE LOOP
FOUR TIMES.
RANGER
382
Range( ) defines where a counter starts, ends, and what number
it should count by. The parameters include (start, stop, step).
The start and stop parameters name the start and stop numbers
for the counter. The step parameter tells how much the counter
should count by. For example, range(4, 13, 4) will count from
4 to 12 (the number before the “stop” number) in increments
of 4; the numbers counted in this range are: 4, 8, 12.
STEP 5: End the first line of the for loop with a colon (:).
Here’s what a for loop, with a counter variable named i,
counting by 1 from 0 up to 3, looks like:
Start with “for.”
Specify how many times
the loop will repeat.
for i in range(3):
Add a colon.
Add “in.”
Name the counter variable.
Below the first line of the for loop, add the code to
be repeated.
Indent the code to be repeated by pressing the TAB key
on the keyboard once or by using the space bar to add FOUR
SPACES. In Python, the indent indicates that the code on
that line is part of the code above it. You can add a print
383
function to the loop by starting a new line and indenting it
in the same way.
FOR EXAMPLE,
you could add a print function that
displays “Hip hip hooray!”
for i in range(3):
print("Hip hip hooray!")
Insert the code you want repeated.
Indent one tab (four spaces).
This will print:
Hip hip hooray!
Hip hip hooray!
Hip hip hooray!
You can add code that runs after the loop has finished running.
To do that, start a new line that’s not indented, like this:
for i in range(3):
In the loop
print("Hip hip hooray!")
print("Congratulations")
Outside the loop
384
This will print:
Hip hip hooray!
Hip hip hooray!
Hip hip hooray!
Congratulations
Every time you create a for loop, you also create a new
variable that counts the number of times the loop is repeated.
That means the variable can be used within the repeated code.
In the previous example, the variable “i” was used in the for
loop. Printing the value of “i” before “Hip hip hooray!” shows
how the value increases each time the loop is run:
for i in range(3):
REMINDER: The
print(i, "Hip hip hooray!") range( ) function
starts counting
at 0 and stops
This will print:
counting before the
number set in the
parentheses.
0 Hip hip hooray!
1 Hip hip hooray!
2 Hip hip hooray!
In the display output, the “i” variable value in the first run of
the loop is 0 and the last run shows “i” having the value of 2.
385
The counter variable can be used to count in other ways.
FOR EXAMPLE,
you could make a countdown. To do this,
subtract the counter variable from 10, and the computer will
display a countdown from 10 to 1:
for i in range(10):
print(10 - i)
This will print:
10
9
8
7
6
5
OOOH
4
AHHH
3
2
1
The range( ) function is set to 10, but can go as high as you
want it to.
386
You could use the other parameters in the range( ) function to
count by 2s between 2 and 10:
Start at this number.
for i in range(2, 10, 2):
Count (step) by this number.
print(i)
End before this number.
This will print: 2, 4, 6, 8,
WHO DO WE
APPRECIATE?
2
4
6
8
To print every item in a list (like “fruits”) use this code:
fruits = ['pears', 'oranges', 'mangos', 'cherries', 'bananas', 'apples']
item in list
for i in range(6):
print(fruits[i])
list name
This would print:
pears
oranges
mangos
cherries
bananas
apples
387
There’s an easier way to loop through an entire list without
having to know the exact length of the list.
Instead of using the range( ) function, use the list itself, and
the loop will run the same amount of times as the number
of items in the list. Instead of being a number, the counter
variable value will be set to each item of the list as it steps
through the entire list.
To print every fruit in the “fruits” list, replace range( ) with
the list name:
fruits = ['pears', 'oranges', 'mangos', 'cherries', 'bananas',
'apples']
Use the list name instead of range( ).
for i in fruits:
print(i)
The variable value of i is the
list item, not a number.
388
w
1. Explain what the range( ) part of a for loop does.
2. Which part of a for loop’s code should be indented?
3. What are two ways to print each item in the
following list?
Seasons = ["Winter", "Spring", "Summer", "Fall"]
Turn the page for question #4
389
Write the output for each of the programs below:
PROGRAM PROGRAM RESULT
NAME
A for i in range(4):
print(i)
B for i in range(10):
print(i * 5)
C for i in range(25, 101, 25):
print(i)
colors = ["red", "blue",
"yellow"]
D for i in colors:
print(i)
print("Those are the primary
colors")
multiplier = 4
E for i in range(11):
print(i * multiplier)
F for i in range(7):
print(i)
390
The range( ) function defines where the loop
counter starts, ends, and what number it
should count by.
Code D: red
results: green
A:
0 blue
1 yellow
2 Those are the primary colors
3
E:
0
B:
0 4
5 8
10 12
15 16
20 20
25 24
30 28
35 32
40 36
45 40
C: F:
25 0
50 1
75 2
100 3
4
5
6
392
30
Chapter
WHILE LOOPS
AND
NESTED LOOPS
WHILE LOOPS
WHILE LOOPS
repeat as long as
REMINDER:
the conditional statements within
A conditional
them are True. A while loop looks statement runs a
chunk of code only
similar to a for loop, but it replaces
when a certain
the counting portion with a
condition is met.
CONDITIONAL STATEMENT.
While loops always start with the key word “while” followed
by a Boolean expression and then a colon (:). The repeated
code is indented below the first line.
393
You could make a password checker that will continue to loop
until the user types in the correct password. The Boolean
expression checks if the entered password is true. To do this:
Create the variable “password” and
“None” is a Python
assign it the value None. key word that
means “empty.”
Create the variable “password” before
you use it in the while loop.
This while loop
password = None
will continually
while password != "myPassword1234": loop as long as
the password
password = input("Enter the password: ")
entered is NOT
if password != "myPassword1234": the same as
“myPassword1234”.
print("Your password is incorrect.")
print("Correct password. Welcome.")
This condition will only run
the print( ) function if the
password variable value is not
equal to “myPassword1234”.
The print( ) function will run
after the password variable value
DOES equal “myPassword1234”.
394
Example output:
Enter the password: rememberMe
Your password is incorrect.
Enter the password: CantRemember
Your password is incorrect.
Enter the password: OhNowIDo
Your password is incorrect.
Enter the password: myPassword1234
Correct password. Welcome.
The program will continue the loop and prompt the user to
enter the password until the user enters “myPassword1234”.
When that happens, the loop ends and the rest of the program
(printing “Correct password. Welcome.”) is allowed to run.
Infinite Loops
INFINITE
In Python, loops (forever loops) are while loops
that use a Boolean statement that can never become false.
These are all infinite loops because there is no way for the
Boolean statements in each to become false:
while True:
print("This is the song that never ends.")
while 4 > 3:
print("This is the song that never ends.")
395
while "hello" == "hello":
print("This is the song that never ends.")
while 5 <= 5:
print("This is the song that never ends.")
None of these loops provide a way for the conditional
statement to ever become false, so these loops will continue
to loop forever (infinitely). The print( ) statement in each
example will continuously loop and
I’VE BEEN
print over and over again, forever. ON THIS THING
FOREVER.
You can exit an infinite loop
by pressing Ctrl + C on Windows,
or command + C on a Mac.
Sometimes you write an infinite loop as part of your
program on purpose. For example, video games usually use
an infinite loop to animate
the characters, continually I’M GONNA
PASS OUT.
updating character movement
and interaction as the player
plays the game. But other
times, an infinite loop may
be written by accident,
and it may crash your
396
computer because the program is too large or tries to get
the computer to process too much information.
NESTED LOOPS
NESTED LOOP
A is when one loop is put inside another
loop. They help create more complex repeating code. For
example, you can use a password program as an outer
while loop and nest an inner for loop to print out all the
wrong guesses the user inputs before they guess the
correct password:
Creates a new list type variable
password = None and assigns it an empty list value
attempts = []
while password != "myPassword1234":
password = input("Enter the password:")
Adds the user’s
attempts.append(password) input to the
attempts list
if password != "myPassword1234":
print("Your password is incorrect. You have already
guessed:")
This for loop prints out all the items
for i in attempts: in the attempts list (the password
attempts the user has entered).
print(i)
print("Correct password. Welcome.")
There is an additional indent for the print( ) function to show
that this code is inside the nested for loop, not the outer
while loop.
397
w
1. What’s the difference between a while loop and a for loop?
2. A while loop that uses a conditional statement that will
always be true is called .
3. What keys do you press to get out of an infinite loop?
4. Describe how a tab (or 4 spaces) is used in nested loops.
5. Write a loop that will give the following results.
PROGRAM PROGRAM RESULT
NAME
A The program will print:
Go! Go! Go!
as long as the variable “x”
is more than 50.
B The program will print:
Good morning, Steve
as long as the variable
“name” is equal to “Steve”.
398
PROGRAM PROGRAM RESULT
NAME
C The program will count
from 7 to 11 by twos 3 times.
D The program will count to 5
over and over again, forever.
E The program will print:
hip hip hooray
hip hip hooray
hip hip hooray
F The program will print:
1
2
3
4
5
G The program will print:
hello, friend
. . . forever, or until the
program is stopped using
Ctrl + C.
answers 399
D.
count = True
while count:
for i in range(1, 6, 1):
print(i)
Variable names may be different.
E.
for i in range(3):
for j in range(2):
print("hip", end=" ")
print("hooray")
Variable names may be different.
F.
num = 0
while num < 5:
num = num + 1
print(num)
Variable name may be different.
G. while True:
print("hello, friend")
401
999, 1000 LOOPS!
YOU KEEP READING AND
I'LL KEEP RUNNING!
402
31
Chapter
CONDITIONAL
STATEMENTS
CONDITIONAL STATEMENTS
CONDITIONAL STATEMENTS
in Python always start
with the key word “if,” followed by the Boolean expression
and a colon. The code that runs if the condition is true is
added below the first line and
Boolean expressions use
indented one tab (or four spaces).
==, !=, <, >, <=, and >=.
if = = <
<=
!=
=
403
FOR EXAMPLE,
you can write a program that displays
a message if a game player has reached the expert level.
The code that prints “Skill Level: Expert” will run only if the
xp (experience points) is greater than or equal to 90. If the
xp is less than 90, nothing happens.
xp = 120 Start with “if.”
Add the conditional statement
and a colon after it.
if xp >= 90:
print("Skill Level: Expert")
Indent here to show this print( ) function
is the code to run if xp >= 90.
Skill Level: Expert will print because 120 > 90.
Else Statements
ELSE
An statement is a statement that runs when the
Boolean value is False. To use the else statement, type “else”
on a new line. Then, on a new line, indent 1 tab (4 spaces)
and add code that will run if the Boolean expression is false.
For example, you could say: If xp is greater than or equal to
90, then display “Skill Level: Expert”, but if the user’s xp is
less than 90, display “Skill Level: Novice.”
404
xp = 50 tells what code
should run when the
if xp >= 90:
Boolean expression
print("Skill Level: Expert") is False
else:
print("Skill Level: Novice")
The example will display “Skill Level: Novice” because
xp is 50, which is not greater than or equal to 90.
Elif THE CELEBRITY
COUPLE NAME
ELIF is used to combine an else FOR IF AND ELSE
WOULD BE ELIF!
statement with another conditional
statement to check for additional
information. Elif is used only after
an “if” or another “elif” statement.
Next to elif, add a Boolean expression
and then a colon.
For example, you can add another experience level to the
game by adding an elif statement to the code.
The first condition displays “Skill Level: Expert” if xp
is greater than or equal to 90.
You can add an elif statement to display “Skill Level:
Intermediate” if xp is greater than or equal to 50 and
405
less than 90. If xp is less than 50, then the else statement
will run the code to display “Skill Level: Novice.”
xp = 50
if xp >= 90:
print("Skill Level: Expert") WHAT?
YOU’RE STILL
elif xp >= 50:
A NOVICE??
print("Skill Level: Intermediate")
else:
print("Skill Level: Novice")
A flowchart of the program shows
the different branches for each
condition:
Start
True
xp >= 90? Skill Level: Expert
False
True
Skill Level: Intermediate
xp >= 50?
False
Skill Level: Novice
406
Compound Conditional Statements
COMPOUND CONDITIONAL STATEMENT
A is a
conditional statement that contains two Boolean expressions.
For example, you could make a game where the player gets
bonus points if their score is greater than 50 AND their
difficulty setting is set to “hard.”
LOGICAL OPERATORS
combine multiple Boolean
expressions or values that evaluate to one Boolean value.
Python uses three logical operators:
AND: If both expressions are True, then the whole condition
is True. If one or both of the expressions are False, then the
whole condition is False.
OR: If one or both expressions are True, then the condition
is True. It doesn’t matter whether the other condition is True
or False.
NOT: Switches the expression
When we talk or write about
to its opposite (from True to
AND, OR, and NOT, we use all
False and False to True). caps; however, within Python
programs, the words are
written in all lowercase.
407
FOR EXAMPLE,
we could display a special message if
a player wins on the most difficult setting and their xp is
greater than 90.
The compound conditional statement starts with “if”, and
then we can add a Boolean expression followed by the
logical operator “AND” and the other Boolean expression:
First Boolean
expression
xp = 150
difficulty = "Hard"
Second Boolean
expression
if xp > 90 and difficulty == "Hard":
print("You surpass all expectations!")
You
surpass
all
expectations!
408
Examples of how logical operators work:
3 < 4 and 6 == 6
True AND True evaluates to True
4 != 4 and 6 > 2
False AND True evaluates to False
5 == 5 or 6 < 3 True OR False evaluates to True 4 > 12 or 7 != 7
False OR False evaluates to False
not(6 < 13)
True evaluates to False
409
| TRUTH TABLES | list all the possible outcomes of logical |
|---|
operators. Truth tables for AND, OR, and NOT:
AND TRUTH TABLE
| Boolean 1 | AND | Boolean 2 | Evaluates to |
| --------- | --- | --------- | ------------ |
| True | AND | True | True |
| True | AND | False | False |
| False | AND | True | False |
| False | AND | False | False |
OR TRUTH TABLE
| Boolean 1 | OR | Boolean 2 | Evaluates to |
| --------- | --- | --------- | ------------ |
| True | OR | True | True |
| True | OR | False | True |
| False | OR | True | True |
| False | OR | False | False |
410
NOT TRUTH TABLE
| NOT | Boolean | Evaluates to |
| --- | ------- | ------------ |
| NOT | True | False |
| NOT | False | True |
Nested Conditional
NESTED
Statements
CONDITIONALS
NESTED CONDITIONAL
| STATEMENTS | can be nested | |
| ------------ | ---------------- | --- |
within loops.
Loop
| FOR EXAMPLE, | you could make a game that loops until | |
| ------------- | --------------------------------------- | --- |
the game is over. The game play could be controlled using
compound and nested conditionals.
Suppose you are creating a game where the user has to
enter as many three-letter words as they can. If they
repeat a word, the game is over. You can use a flowchart
to map out the order and direction of actions.
411
Start
Yes
Is game == “play”?
End No Print “Enter a 3-letter word:”.
Set input to “new” variable.
No
Is new word Is length of new word
already in list? greater than or less
than 3 letters?
No
Yes Yes
Print “Nice one.”
Add word to words list. Print “That’s not a
3-letter word.”
Set game = “over”.
Print “You already entered that word.”
Print “You know _ 3-letter words.”
412
Using the flowchart as a guide, you can create the program:
words = [] Creates a blank list called “words”
Starts a while loop for game play
game = "play"
Sets the variable “new"
while game == "play":
to the user input
new = input("Enter a 3-letter word: ")
Checks if the word is
if len(new) > 3 or len(new) < 3: 3 letters long
print("That’s not a 3-letter word.")
Prints if word is not 3 letters long
else:
If the word is 3 letters, it moves on to the code below.
if new in words:
If the word is already in the
list, it breaks out of the loop.
game = "over"
print("You already said that word. Game over.")
print("You know", len(words), "3-letter words.")
If the user enters a word they already Tells how many
used, it prints the game over message. words in the list
413
else:
If the word is unique,
print("Nice one.")
it prints this.
words.append(new)
It also adds the word
to the list.
The nested conditional is:
If the word is three letters long AND unique, the game
continues.
I KNOW SO MANY
THREE-LETTER WORDS!
414
w
1. Label each of the following with the type of conditional
statement it represents (if, if/else, if/elif/else):
A. if at_dance == True:
print(“Dance the night away.”)
elif busy != True:
print(“Go to the dance.”)
else:
print(“Stay home.”)
B. if hands != “sweaty”:
print(“hold”)
else:
print(“wipe hands”)
C. if courage > 50:
print(“Say hello to your crush.”)
elif courage < 10:
print(“Don’t make eye contact.”)
else:
print(“Smile at your crush.”)
More questions 415
D. if breath != “sweet” and crush_distance < 10:
print(“Go brush your teeth, now!”)
E. if crush == “at movies” or friends == “at
movies”:
print(“Go to the movies.”)
else:
print(“Stay home and chill.”)
416
Write the output for each of the following programs:
num = 3
A. if num >= 3:
print("Greater than 3")
B. shape = "square"
if shape == "circle":
print("you win")
else:
print("no such luck")
C. color1 = "red"
color2 = "blue"
if color1 == "red" and
color2 == "yellow":
print("orange")
elif color1 == "red" and
color2 == "blue":
print("purple")
else:
print("green")
D. fact = not(5 == 4)
print(fact)
More questions 417
What does the AND logical operator do?
Write a program for the following flowchart.
Is size
| No | Yes | |
| --- | --- | --- |
“large”?
| Is color | Is color | |
| --------- | --------- | --- |
| “orange”? | “gray”? | |
Yes Yes
| print: “You probably | No | print: “Look out |
| --------------------- | --- | ----------------- |
| own a goldfish.” | | for sharks!” |
No
print: “Your fish print: “Do you see
could be tropical.” a whale?”
1.
A. if/elif/else
B. if/else
C. if/elif/else
D. if
E. if/else
2.
A. Greater than 3
B. no such luck
C. purple
D. True
3. The AND operator combines two Boolean expressions to
make a compound conditional statement. A compound
conditional statement that uses AND is True only if both
Boolean expressions within the statement are True.
420
C.
Do you like being Yes
No bored?
print: “Do nothing.”
Do you like Yes
to read?
No Do you like to read
a lot?
Yes
print: “Read a magazine.”
print: “Read a novel.”
6. if size == "large":
if color == "gray":
print("Look out for sharks!")
else:
print("Do you see a whale?")
else:
if color == "orange":
print("You probably own a goldfish.")
else:
print("Your fish could be tropical.")
7. You probably own a goldfish.
422
32
Chapter
FUNCTIONS
Functions are blocks of code
The words function and
that you can use to build a
procedure mean almost the
bigger program. You can add same thing. When talking
about Python, we refer
more premade functions by
to function (some people
importing modules.
might say “procedure”).
A kind of library
TURTLE GRAPHICS
A library is a
The TURTLE MODULE is filled with collection of
functions that allow you to treat the prewritten functions
and code that can
screen like a drawing board and use
be imported into
the turtle icon to draw on it. a project.
423
Importing the Module
You can import the turtle module
using the import command. Start
with the word “from,” then enter the
module name, and then enter “import,”
which means you want to import from
the named module (in this case, “turtle”).
You can name which specific functions you want to import
from a module. To import all the functions, end the import
command with “*”.
Import command key word
from turtle import *
Means “all”
Module name
This means import all the functions from the turtle module.
Moving the Turtle
After importing the turtle module, you can use its functions
to move the turtle around the screen. The turtle starts out
facing to the right. You can make the turtle move using the
forward and backward functions.
The default “turtle” is actually just a triangle
that points in the direction it’s facing.
424
FOR EXAMPLE,
you can make the turtle move forward
PIXELS
100 on the screen with the command:
Parameter/distance
forward(100)
Function
This is what the code looks like:
from turtle import *
forward(100)
The command
will open a new
window and
draw a line
from left to right
that’s 100 pixels
long (the triangle
at the end of the
line is the turtle):
425
PIXEL
A pixel (from picture element) is a point of light on a screen.
The small points make up images on a computer display.
The left( ) and right( ) functions turn the turtle left or right based
on the direction it is facing on the screen. Both of the functions
require a parameter for the number of degrees they turn.
FOR EXAMPLE,
to turn 90 degrees to the left, use:
Parameter/degree
left(90)
Function
You can use the turtle functions along with other parts
of Python.
FOR EXAMPLE,
you could use loops to make some
interesting art. A for loop that repeats 6 times along with
forward and right functions from the turtle module can be
used to draw a hexagon:
This directive tells the turtle to
from turtle import * repeat the following code 6 times:
move forward 70 pixels, then turn
for j in range(6): right 60 degrees.
forward(70)
right(60)
426
The code
repeated
6 times will
draw this
hexagon.
You can also nest the hexagon loop inside another loop
that rotates by 5 degrees after each hexagon is drawn.
By repeating the outer loop 72 times, you can draw
72 hexagons, each 5 degrees rotated to the right.
from turtle import *
for i in range(72)
for j in range(6):
forward(70)
right(60)
right(5)
427
Here’s what the
drawing looks like
after running the
program:
Additional Turtle Art Functions
There are many more functions in the turtle module that can be
used to create fun art.
FUNCTION DESCRIPTION
forward( ) Moves the turtle forward; parameter is number of
pixels to move
backward( ) Moves the turtle backward; parameter is number
of pixels to move
right( ) Turns the turtle clockwise; parameter is number of
degrees to turn
left( ) Turns the turtle counterclockwise; parameter is
number of degrees to turn
penup( ) Picks up the turtle’s pen (ends tracing the
movements of the turtle); no parameters
428
FUNCTION DESCRIPTION
pendown( ) Puts down the turtle’s pen (begins to trace the
movements of the turtle); no parameters
pencolor( ) Changes the color of the turtle’s pen; parameters
are named colors
heading( ) Returns the current heading-useful if you need to
know which way the turtle is facing; no parameters
position( ) Returns the current x and y position-useful if you
need to know where on the screen the turtle is; no
parameters
goto( ) Moves the turtle to a specific position; parameters
are x-axis and y-axis coordinates
fillcolor( ) Changes the color the turtle will use to fill a
polygon; parameter types are the same as
pencolor( )
begin_fill( ) Remembers the starting point for a filled
polygon-used before a shape you want to fill is
drawn; no parameters
end_fill( ) Closes the polygon and fills with the current fill
color-used after a shape you want to fill has been
drawn; no parameters
dot( ) Draws a dot at the current position; no parameters
stamp( ) Stamps the image of the turtle shape on the screen
wherever the turtle is; no parameters
shape( ) Changes the shape of the turtle; parameters are
“arrow,” “classic,” “turtle,” “circle,” or “square”
Even though some functions don’t use parameters, you still need to
include the parentheses ( ).
429
FUNCTIONS
If you’re using the same piece of code over and over in
Python, then it’s best to make your own function. When you
DEFINING A FUNCTION
make a new function, it’s called .
To define a function, use this format:
Start with “def” for “define”
def functionName( ):
Name the function whatever
print("hello") you want (using the same rules
as naming variables), add
parentheses, end with colon
Indent and add your code
CALL A FUNCTION
To
I’M
is to use a function GONNA
CALL HIM. YOU CAN’T. YOU
that is already defined. DIDN’T GIVE HIM
A NAME!
When you call a function,
Python finds the
function definition and
runs the code found in
the function body.
430
I AM GOING
You can only call a
TO CALL YOU
function after it has THOR.
been defined. To call a COME, THOR!
COME WHEN I
function, use this format: CALL YOU!
FUNCTION NAME
functionName( )
PARENTHESES
Whenever you call a function, The body of the
the program jumps back to where function is the
indented part. The
the function was defined, runs all the
body is the code that
code in the body of the function, then will run when the
function is called.
goes back to where the program left
off when the function was called.
def functionName():
functionName()
431
Here’s an example of a function that says “Hello, World!”:
Defines function
def hello( ): Body of function,
code that will run
print(“Hello, World!”)
hello( )
Calling the hello function
This will print: Hello, World!
PARAMETERS AND
RETURN VALUES
Parameters and variables are similar because they are
PARAMETER
both used to store information. However, a is
different because it cannot be used outside a function. A
parameter is data that
is provided as input from
WHO ARE
FUNCTION
a user. Functions can use
YOU?
parameters only within
the body of the function.
That’s because a
parameter in a function
is only recognized within
PARAMETER
the function itself.
432
FOR EXAMPLE,
you can create a function that converts
meters to feet. Inside the convert function, you can multiply
the meters parameter by 3.281 (the number of feet in 1 meter)
to get how many feet are in the specified number of meters.
Function definition Parameter name
def convert(meters):
Use the parameter like a variable.
feet = meters * 3.281
return feet
Call the function and include the
value of the parameter, in this case 1.
convert(1)
If you tried to use the meters parameter outside of the
function definition, you’d get an error:
def convert(meters):
feet = meters * 3.281
print(feet)
Function definition ends here.
convert(3)
“Meters” used outside the function
print(meters) definition results in an error.
NameError: name "meters" is not defined
433
RETURN VALUE
The of a function is the information that
you can pass from the function back out to the main program.
This is the function’s output. To pass information out of the
function, write “return” followed by the output data.
Return value = function output
def convert (meters):
feet = meters * 3.281
This will return the value of feet
return feet each time the function runs.
With the convert function defined, you could
call the function many times and get
a different return value each time.
convert(5) returns 16.405 (5 * 3.281)
convert(234) returns 767.754 (234 * 3.281)
convert(5,234) returns 17,172.754 (5.234 * 3.281).
To print the return value, use the print( ) function with the
function call inside it:
print(convert(1))
Function call
The program will print: 3.281
434
You can also add text around the function call to give an
explanation of the code, like this:
print("3 meters = ", convert(3), "feet")
The program will print:
3 meters = 9.843 feet
HEY, I GOT A REQUEST TO RUN THE
CONVERT FUNCTION AND THEY’RE
GIVING ME 2 AS AN INPUT.
SURE THING. I’VE GOT THE
FUNCTION DEFINITION
RIGHT HERE.
435
You can repeat a small chunk of code while using a
parameter to slightly change it for each use. For example,
in a word game program, instead of typing “Please enter
a noun” or “Please enter an adjective” repeatedly, you could
make a function to do it for you:
Creates a new variable called "words" and assigns it a blank list
words = [] Defines a new function called "prompt"
def prompt (kind):
The kind of word
the user will be
asked to enter
ask = "Please enter " + kind + ": "
word = input(ask) The user is asked to
enter a type of word.
words.append(word)
The variable "word" is
assigned the value of
what the user enters.
The value for "word"
is added to the list
called "words".
436
prompt("an adjective")
The type of word
prompt("a nationality") the user will enter
prompt("a person")
prompt("a plural noun") The "prompt" function can be called
many times, asking the user for
prompt("an adjective")
different types of words by changing
prompt("a plural noun") the parameters for each function call.
The word list, created by the user‘s input, is inserted into the
word game:
print("Computers were invented by a", words[0], words[1],
"engineer named", words[2], ". To make a computer, you need
to take a lot of", words[3], ", melt them down, and make",
words[4], words[5], ".")
The output for this program is a completed story that uses
the user’s words to fill in key details.
437
w
1. How do you import all the functions in the turtle module
into a Python program?
2. Write out the two lines of code you would need to move
the turtle 45 pixels and turn right 30 degrees (assuming
you’ve already imported the turtle module).
3. What does it mean to call a function? What code would
you write to call a function called “BopIt” with no input
information?
4. When you create a new function, you need to it.
5. You can pass information into a function using .
6. You can pass information out of a function to the main
program by using .
7. Explain what’s wrong with the program below:
def distance (laps):
meters = laps * 100
return meters
print(laps)
438
NAME CODE RETURNS
def absolute_value(num):
C. if num >= 0:
return num
else:
return num * -1
absolute_value(-4)
D. def favorite(category, thing):
sentence = "My favorite " +
category + " is the " + thing
return sentence
favorite("snake", "Python")
440
9.
A. Hello Max
B. Plot a course through 3 and 5
C. 4
D. My favorite snake is the Python
CHOOSE
WISELY!
442
Unit
8
Web
Development
444433
33
Chapter
WHAT IS THE
INTERNET?
COMPUTER NETWORKS
NETWORK
A is a group of connected computers.
For example, the computers, phones, and other devices
that your family owns are all part
NETWORK
of your home computer network.
A group of connected
When you get a new tablet and
computers that
enter in the Wi-Fi password, you’re share information
and resources
joining that tablet to your home
computer network.
Devices in the same network can easily communicate and
share resources with each other. For example, computers on
a coffee shop’s wireless network all share internet access,
and a family’s phones may be able to control their TV.
444
Local Area Networks
LOCAL AREA NETWORK (LAN)
A is a type of network
made up of nearby computers. A LAN can have anywhere
from a few devices (like a home network) to hundreds of
devices (like a school or hospital). Large organizations like
colleges can have multiple LANs-maybe one per building.
A wide area network (WAN) is made
of connected LANs that are far from each other
(like in different parts of the country or world). WANs
connect thousands or even millions of devices.
Communicating
on a LAN
Computers in a network
ETHERNET
communicate with
WIRELESS
(with wires) or
(without wires).
Ethernet was developed in the
PROTOCOL
1970s. It’s the ,
PROTOCOL
or rules, for how devices
A standardized set
communicate using cables to of rules
physically connect. Wireless was
445
developed in the late 1990s. It’s the protocol for using radio
waves to send information through the air to connected
devices.
ETHERNET
Rules that computers
follow for communicating
on a wired network
ETHERNET
WIRELESS
Rules that computers
follow for communicating
on a network through
radio signals
WIRELESS
446
Wi-Fi is a popular way to connect wirelessly to
a network. “Wi-Fi” is believed to be short for “wireless
fidelity,” which is taken from the term “high fidelity”—
used to describe high-quality audio.
THE INTERNET
INTERNET
The is a world-wide Many places have
their own networks.
system of connected computer
Schools, coffee
networks. It’s a giant network of
shops, even malls
smaller networks. At home, your almost always have
their own networks
family’s phones, computers, and
to connect to
other devices are all part of your
the internet.
home computer network sharing
a connection to the internet.
HOME NETWORK THE INTERNET
HELLO
447
The Web Origin Story
The modern internet began in the early 1990s, when
TIM BERNERS-LEE created the tools and framework for
the World Wide Web. In a few months, he created:
WEB BROWSER
the first web browser, called
WORLDWIDEWEB and
later renamed NEXUS.
YOUTUBE.COM
(Now we can choose
between Chrome, Safari,
Microsoft Edge, and other
browsers.)
HTML
HYPERTEXT MARKUP LANGUAGE
(HTML), the language that is
used to create the structure of
HELLO, WORLD!
a website.
HYPERTEXT TRANSFER PROTOCOL
(HTTP), a major way to send HTTP
information over the internet.
Web browsers use HTTP to
communicate with
the computers that
store websites.
448
The World Wide Web created a new era of communication.
There are now many millions of devices and applications
connected to the internet.
SENDING INFORMATION
OVER THE INTERNET
When you download an item from
PACKETS
the internet, such as music to your
Small units of
phone, the songs are too big to
data that are sent
send all at once. Instead, each in binary code
song is broken up into PACKETS , through a network
which are sent individually and
then recombined on your phone.
Each packet has a destination address and a packet
number that tells the network where to send it and
how to reassemble all the packets when they reach
the final destination.
IP (INTERNET
PROTOCOL)
IP ADDRESS
An is used to direct
Rules for transferring
packets to the right network. IP
information on
addresses are unique addresses the internet
Every computer has its own MAC (Media Access Control)
address made up of 16 digits and letters, which
identifies the manufacturer and the specific model.
449
that label devices on a
network and the internet. INTERNET
Every device has its own SERVICE PROVIDER
A company that provides
IP address. IP addresses
people access to the internet
can change and are
assigned by an internet
service provider.
IF COMPUTERS EACH BECAUSE THAT'S HOW WE
HAVE THEIR OWN DO IT, OK?! THAT'S JUST
MAC ADDRESS, HOW THE PROTOCOL!
COME THE INTERNET
DIRECTS PACKAGES
TO A NETWORK, NOT
A DEVICE?
450
USING THE INTERNET TO
SURF THE WEB
≠
INTERNET WORLD WIDE WEB
INTERNET
The is the connection
and network between devices. You
can use the internet to connect to
and surf, or explore, websites.
WORLD WIDE WEB
The , or web, is a collection of websites
that are linked together through the internet. The web is the
content you can view, read, listen to, stream, and download.
Most websites have links that connect them to other
websites. If you were to draw an image of all these links,
it would look like a spiderweb made of websites around the
globe. That’s why it’s called the World Wide Web.
THE WEB
youtube.com
facebook.com
coolmathgames.com
websites
internet
451
When you open a website on your computer, you are opening
HTML FILES
a temporarily downloaded copy of the that
make up that site.
HTML stands for “hypertext markup language” and is a
language that is used to create websites. The “hypertext”
part of the name means that the language is built for
connecting websites together through links. Because websites
are linked (by the internet), you are able to use HTML to jump
from one site to another.
Every website is stored on a "May I look at
www.usa.gov?"
computer. When you open a web
browser and type in a website,
you are asking the computer on user's
Host
computer
which the website is stored to
send you a copy of the site. The
computer where a website is
"Sure! Here's a copy."
HOST
stored is called a .
A host can be an ordinary computer, but most of the time
SERVERS
hosts are specialized computers called . Servers
have massive amounts of storage, have fast internet
connections, and run specific software. This makes it easier
for them to store all of a website’s information.
452
Your computer downloads the
HYPERTEXT
website using a list of rules
TRANSFER
HYPERTEXT
called
PROTOCOL (HTTP)
TRANSFER PROTOCOL
The rules for sharing
(HTTP) web content. Web browsers
. Website addresses
use HTTP to communicate
start with HTTP or HTTPS
with servers.
(a more secure version of
transferring files). HTTP is a
major way in which all websites are sent over the internet.
HYPERTEXT TRANSFER
PROTOCOL SECURE (HTTPS)
Shares the same function as HTTP but adds a layer of
security by encrypting, or coding, all transferred data
FOR EXAMPLE,
part of HTTP is a set of status codes that
are sent from the server to the browser. These codes tell the
browser what’s going on with the server. An example of a
status code is 404 NOT FOUND.
The 404 Not Found code lets the browser know that the
server couldn’t find the website that the browser asked for.
453
Finding Where a Website Lives
UNIFORM RESOURCE
Every website on the internet has a
LOCATOR (URL)
or address.
Before you can access a website, your computer needs to
find out which server stores the site you need. When you
type a web address into your web browser, your computer
COMPUTER
1. What's the IP address for USA.gov?
USA.GOV
3
.
C
a
n
4
. Sure!
H
I
ac
c ess
U
SA
ere
y
ou
go!
.gov?
IP ADDRESS:
54.85.132.205
<br/>SERVER<br/>UNITED STATES<br/>GOVERNMENT<br/>
454
DOMAIN NAME
first asks a
DOMAIN NAME
SYSTEM SERVER
for the
SYSTEM (DNS)
IP address of the server that is Databases that
hosting the site. Your computer translate website URLs
to IP addresses.
can then use that IP address
to find the correct server and
ask the server for access to the HTML files that make up a
website. All of this happens in less than a second.
DNS SERVER
2. It's 54.85.132.205.
The DNS server works like the contact list on your phone.
You select your friend’s name from the list, and the phone
calls the number linked to your friend. You don’t have to
memorize your friend’s phone number, just like we don’t
have to memorize a website’s IP address. But you could call
your friend by entering their phone number, just like you
could access a website by entering its IP address.
455
Popular websites are hosted
Every minute, millions of
on many servers throughout
people use the internet to
the world. This helps to keep the view a wide variety of things.
That’s why the internet
site running quickly when many
needs protocols to keep
requests to view the site are
things organized.
made at the same time. It also
helps to prevent outages if one
server goes down. Users are probably
connected to the closest server.
The Transmission Control Protocol
Once your computer connects to
the host server, the server follows TCP
TRANSMISSION CONTROL A set of rules computers
use when they are
PROTOCOL (TCP)
. Devices
transferring information
use TCP when all the requested across the internet
information (website, picture,
video) needs to be transferred.
FOR EXAMPLE,
when you load a website, the server
sends you the site information as small packets. If a
packet gets lost along the way (usually due to a lost
or weak connection), your web browser will send a
new request for the missing packet. It will keep
sending the request until it receives the packet and
the entire site is loaded.
456
YOUR
TCP
COMPUTER SERVER
I
N
EED
P A Breaks site
I N
I
N EED
P A
C
K ET
1
into packets
I N EE
E
D
E D
P
P
A C K ET
C
3
K ET
2 1
1 2
A
C K ET 2 3 4
G 4
N
DI 3
N G
E N
S DI
N
E G
S N
DI G 4
1 N N
S
E DI
N
E
S
2
I
3
S T
I L L L O S
T!
N
E
E
D
P
1 2 A
C
K
3 4 E T
4
4
SENDING
4
Puts site
back together
457
The User Datagram Protocol
USER DATAGRAM PROTOCOL (UDP)
is another way
to transfer information. It focuses more on speed than on
getting every single packet to the final destination. This
protocol is used when speed is more important than getting
all the requested information.
FOR EXAMPLE,
video conferencing services like Google
Hangouts or Skype use UDP because users would rather keep
the video call going, even if the image gets fuzzy, than pause
the call and wait for every last pixel to load. A computer
running a video conferencing service won’t request the
server to resend a packet that it didn’t get.
WHO ARE
YOU?
458
w
1. What’s the difference between the internet and the
World Wide Web?
2. What are packets?
3. Why are protocols necessary to transfer information
and communicate on a network?
4. What is a DNS server?
5. How does a computer know if information sent over
a network is meant for it?
6. Explain what a protocol is. Why is it useful to have
a protocol for network communication?
7. What does a server do and how is it different from
a personal computer?
8. What does “URL” stand for?
9. Why does a video service like Skype prefer to use UDP
protocol?
More questions 459
The internet is the connection between devices,
and the web is the content (including websites,
videos, pictures, etc.).
Servers are computers that have a very fast internet
connection and lots of storage space. They store
websites, videos, pictures, and other information that
users can access through the internet.
34
Chapter
CYBERSECURITY
WHAT IS CYBERSECURITY?
CYBERSECURITY
is needed to keep digital information
safe. Cybersecurity is a set of techniques or ways used to
keep information secret, available, and uncorrupted:
Secret: Information that shouldn’t be
shared with others needs to be kept
private.
Available: Authorized people should be
able to access their files and information
stored on a computer. If someone puts
a virus on your computer that prevents
you from using it, they are making your
AUTHORIZED
information unavailable to you.
PERSON
Someone who
Uncorrupted: Files and information has permission
on a computer should not be
463
changed by an unauthorized VIRUS
person. If someone changes the Software that is meant to
do harm and can spread
password to one of your social
to other computers
media sites and logs on as you,
they have corrupted your account.
CYBERSECURITY
TECHNIQUES
Cybersecurity techniques can:
prevent the wrong
people from gaining
access to information
make it impossible to
use the information,
even if unauthorized
people do get their
hands on it
Usually multiple cybersecurity techniques are used to protect
information.
Authentication
AUTHENTICATION
is the process computers use to
confirm someone’s identity before giving them access
464
to information. Computers can use different kinds of
authentication:
asking for a username and password
scanning a fingerprint
using a camera to recognize your face
TWO-FACTOR AUTHENTICATION
combines two
different kinds of authentication.
FOR EXAMPLE,
to log on to your email account with
two-factor authentication, you may need to enter
your password and scan your finger on your phone.
It’s much harder for attackers to break through
two-factor authentication.
Access Control
ACCESS CONTROL
refers to authorized users having
access to specific files. If you have a user account through
your school, you can access your homework, grades, and
other files that you need. But you can’t access the teacher’s
account to change your grade, view another student’s
information, or download next week’s exam. Access control
uses authentication to prevent the wrong people from
getting data they aren’t authorized to view.
465
Sandboxing
SANDBOXING
is putting an application in a secured
part of the system with limited access to the rest of the
computer system. This way, if an attack is made on the
application, only that application will be affected, and the
rest of the system will stay safe.
CRYPTOGRAPHY
CRYPTOGRAPHY
is a strategy for
I STOLE THE
keeping information
WORLD’S GREATEST
secret. The goal of CHILI CHEESE CORN
DOG RECIPE...
. . . BUT I CAN’T
cryptography is to
UNDERSTAND A
scramble information SINGLE WORD!
and messages so well
that no one except
authorized people
can unscramble
and read them.
This adds another
466
CIPHER TERCES
layer of security beyond access control, so that even if an
unauthorized person gets the secret files, they still won’t be
able to read them.
The process of scrambling and unscrambling information is
ENCRYPTION
called encryption and decryption. is when
readable information is transformed into a secret message,
DECRYPTION
and is the process of returning the secret
message to readable information.
CIPHER
A is the tool used to make information unreadable
KEY
to people who don’t have the . The key is used with the
cipher to decrypt an encrypted message. A cipher is also the
tool that is used to translate a secret message back into its
original, readable form. For example, a bank’s website uses
a cipher to translate customers‘ account information as it is
sent between a computer and their server.
ENCRYPTION
TER
C
E
S
467
Ciphers are much older than computers. The Roman
dictator JULIUS CAESAR (100 BC-44 BC) used one of
the earliest ciphers, which was named
The key to the Caesar
after him. The CAESAR CIPHER shifts
cipher is to move each
each letter forward a fixed number letter forward a certain
number of spots.
of positions, for example, three spots
on the alphabet.
For example, using the Caesar cipher, “Hello, World” would
be encrypted to “Khoor Zruog.”
You could decrypt the message “Khoor Zruog” by using
the key in reverse and shifting each letter backward
three spots.
CRACKING A
The Caesar cipher is easy
CODE OR CIPHER
for some people to crack and When someone finds a way to
decrypt encrypted messages
even easier for computers
without being told the key
to crack.
468
During World War II
(1939-1945), the German The Enigma
military improved the Caesar
cipher with a machine
called ENIGMA. It used a
complicated combination
of different ciphers. Every
letter that was typed in
went through multiple layers of encryption,
and then the key shifted for the next letter. So two
of the same letters in the original message would be
set to different letters in the encrypted version.
Alan Turing (England, 1912–1954): During World War II,
Turing worked on a team tasked with breaking the
German encryption machine, Enigma. His creation,
the BOMBE, was an early computer that succeeded in
decrypting messages coded by Enigma.
HACKERS
HACKERS
are people who
Companies and
break into computers and large governments hire white
hat hackers to help
computerized systems. There are
protect systems and
many types of hackers, and not all
information.
of them are bad.
469
BLACK HAT HACKERS
break into a
system to steal information or do damage.
WHITE HAT HACKERS
hunt for bugs
and other faults to fix them before
black hat hackers can use those
faults to break in.
HACKTIVISTS
break into systems
to accomplish social or political goals.
The term “hacker” also means someone who uses objects
in creative new ways. For example, using your sunglasses
to prop up your phone is a hack, because sunglasses aren’t
meant to be used that way. This definition builds on the
concept of the computer
hacker, who gains access to
a system using code, bugs,
and other digital features
in creative ways.
ATTACKS
Hackers can use different attacks to break into a system.
BRUTE FORCE
A attack is when a hacker uses a computer
to guess every authentication possibility. For example, guessing
every possible password combination is a brute force attack.
470
If you set your password to a 4-digit number, a computer
could guess every number between 0 and 9999 to find your
password within seconds. This is why websites and apps
usually require you to use at least eight characters that
include numbers, symbols, and some capital letters. There
are over 600 trillion combinations you could use to make one
of these passwords, which is why longer, more complicated
passwords are much harder to crack with brute force attacks.
ARE YOU STILL TRYING TO FIGURE OUT
MY PASSWORD? I TOLD YOU IT’S TOO
LONG TO CRACK.
Do the Math
Personal identification numbers (PINs) that are 4 digits
long and use 10 numbers (0–9) have 10*10*10*10 or
104 = 10,000 possible combinations. But a password
that is 8 characters long and uses 10 numbers, 26 lowercase
letters, 26 uppercase letters, and 10 characters has
728 = 722 million combinations.
471
Another way that hackers can access systems is by
MALWARE
using . Malware includes any type of harmful
software installed on a computer.
Malware includes:
Ransomware: keeps a user
from accessing a computer
until they pay the hacker
money.
Spyware: spies on the
user to steal information
like usernames and
passwords.
PASSWORDS
Trojan horse (or Trojan):
Any type of harmful
software that is disguised
as a normal file.
472
Virus: software that
spreads like a disease to
other computers. Viruses
are especially dangerous
within networks since
they can spread to all
computers connected
within that network.
Worm: harmful
software that can
make copies of itself
and spread on its own.
Worms often spread
by sending themselves
through mass emails.
!
!
473
No Coding Required
SOCIAL ENGINEERING
is the
most popular type of attack,
and it doesn’t use coding at all.
Social engineering is when a
person pretends to be someone
else to get what they want.
PHISHING
is one type of
social engineering, where an
attacker pretends to have a
legitimate email address or
website in order to get your
PASSW
ORD
username and password.
FOR EXAMPLE,
an attacker could send out an email that
asks you to log on to one of your social media accounts. But
instead of linking to your actual account, they send you to a
site they set up to look exactly like the real thing. When you
log on to their fake site, you are giving the attacker your
username and password, which they can then use to log on
as you on the real social media site.
474
TIP:
Protect yourself and never give out information that
has been requested through an email. The social media
websites you use already know your password—they will
never ask for it (only social engineers will). When in doubt,
don’t click on the link in an email. Also, be sure to look
closely at URLs: www.amazon.com is a legitimate site, but
www.amaz0n.com is probably a phishing site. There is
a “0” in place of the “o” in the phishing site address.
Distributed denial-of-service (DDoS) attacks are when a
hacker uses lots of computers (probably infected by a virus)
to send so many messages to a server at the same time
that the system is overloaded and crashes. Usually, a hacker
uses a DDoS attack to collect a ransom or to accomplish
a political goal, like shutting down a website they don’t
agree with.
475
w
1. What is cybersecurity?
2. Which cybersecurity technique confirms the user's identity?
3. Which cybersecurity technique isolates an application so
that if it is attacked, other applications are not?
4. Which type of hacker breaks into systems legally?
5. What is a brute force attack?
6. Match the description to the type of malware.
Ransomware can copy itself and spread on its own
Spyware is disguised as a normal file
Trojan spreads like a disease
Virus keeps users from using their computers
until they pay up
Worm spies on the user to steal information
476
The set of techniques used to keep information safe
To encrypt and decrypt messages, making information
unreadable to people who don’t have the key
THEY
CALL ME
CYBER SAFE
CINDY!
480
35
Chapter
CREATING
A BASIC
WEB PAGE
BUILDING BLOCKS OF WEBSITES
HTML CODE
All websites are created using . HTML is what
professional web developers (people who make websites for
their job) use to organize and display text, images, videos, etc.
in a web browser. HTML is used to
tell a web browser what to display. HTML
Stands for Hypertext
Markup Language.
CASCADING STYLE SHEETS
The “hypertext” part
(CSS)
is used by websites to tell means that it connects
websites together, so
the browser how the site should
you’re able to go from
be displayed. You can use CSS to
one site to the next.
change the color of text, insert
a background image, and more.
481
OH, YOU’RE LEARNING SPANISH?
THAT’S NICE. I’M LEARNING FOUR
Early websites were made using LANGUAGES: SCRATCH, PYTHON,
HTML, AND CSS.
only the language HTML and early
versions of CSS, which means ¿QUÉ?
they didn’t have much styling,
interactivity, or animation. Now
there are many languages used
in addition to HTML and CSS
to create lively and interactive
websites. HTML and CSS are used
to create the layout and look of
BEST FRIENDS
a website, while other languages FOREVER
like JavaScript and PHP are used CSS
to run programs that make sites
HTML
more interactive.
TOOLS FOR WRITING A WEBSITE
Professional web developers sometimes pay to use special
code editor programs where they write the code that makes up
websites. However, the TEXT EDITOR that comes preinstalled
on computers (Notepad or TextEdit) can be used as well.
HTML website files are saved as an “.html” file type. For
example, a website called “index” should be saved as
“index.html.”
Tells the browser this is an HTML file
File name
482
You can name your HTML files whatever you want. “Index”
is usually what the main page of a website is named.
Be sure to include “.html” after the name of your file;
otherwise web browsers won’t read it correctly.
VIEWING A WEBSITE
WEB BROWSER
To view a website, you need a . Web
browsers are programs that can read HTML files and
display them as websites on your computer. Examples of
web browsers are Chrome, Safari, Microsoft Edge, and
Firefox.
Go to the folder where your .html file is saved, right-click
(or command click on a Mac), and under the “Open with”
menu, select a browser. When you open your file, the browser
displays the website.
483
WEB PAGE BASICS
CONTENT
All websites contain . Content is the text, images,
or other parts of a website that the viewer sees when they
WEB BROWSERS
look at the site in their web browser. are
programs that can read HTML files and display them as
websites on a computer.
You can read the HTML
code from any site by
right-clicking on the
page in a web browser
WOW.
and selecting “view page CHECK OUT ALL
source.” A new window THAT CODE!
will open, revealing all
the code for that page.
Tags and Elements
ELEMENTS are the parts of the webpage; they are like
building blocks. Each type adds a different detail, or layer,
to what you want to build.
TAGS
are like quotation marks. The opening quotation
mark tells you when a quote begins, and the closing quotation
mark tells you when the quote ends. Start and end tags work
in the same way. They surround each piece of content in the
code for a website.
484
YOU'RE
AN ELEMENT
TAG! NOW!
START TAG CONTENT /END TAG
Tags are important because they tell the computer when an
element begins and when it ends.
Elements are the tags plus the content inside them.
Element = Tags + Content
There are many types of elements, but they all start with
a tag, followed by content, then end with a tag:
Start tag: You place angle brackets
around the name of an element.
Content goes here . . .
content
This whole line makes End tag: like the start tag
up an element. but with a forward slash
485
Elements are used to format text and divide the website
into sections. For example:
ELEMENT DISPLAYS AS
This text is bold This text is bold
web browser, including additional CSS code, the site’s title, or
key words for search engines to look for.
ELEMENT
The is where all the website content
that you see goes. The text, images, videos, animations, and
anything else you want displayed on your site go here.
The head and body of a website can look like this:
<!DOCTYPE HTML>
The title text is
displayed on the
browser tab.
VOLCANO REPORT
SHIELD VOLCANOES SLOWLY OOZE
LAVA, CREATING A BROAD SHAPE WITH
A paragraph
GENTLE SLOPES.
A FAMOUS EXAMPLE OF A SHIELD
VOLCANO IS KILAUEA IN
HAWAII. KILAUEA IS STILL ACTIVE
A paragraph
AND ADDS TO THE LAND MASS OF THE
ISLAND.
FORMATTING HTML
Indentation and white space don’t matter in HTML. Indenting
nested elements makes it easier to keep everything organized.
Indenting the
A famous example of a shield volcano is Kīlauea
in Hawaii. Kīlauea is still active and adds to the land mass
of the island.
start and
end tags.If your tags are nested incorrectly, content may show up
wrong, it would be harder to keep code organized, and it
would make finding errors more difficult.
Incorrect nesting:
A famous example of a shield volcano is Kīlauea in
Hawaii. Kīlauea is still active and adds to the land mass of
the island.
Comments
You can add comments to your HTML code that won’t be
read by the browser. Comments are notes to yourself about
the program. They look like this:
Exclamation point at the beginning but not at the end
Opening and closing tags need to be different so that the
programmer and the computer don’t get confused about
where tagged content starts and stops.
FOR EXAMPLE,
the opening tag, and the opening tag has an exclamation
point while the closing tag does not.
490
NO COMMENTS,
PLEASE.
IT WAS A GIFT.
491
w
1. What are the two most commonly used website
languages? What part of the website does each
language control?
2. What does HTML stand for?
3. Fill in the blanks below to label each part
4. To code an HTML file, you can buy a professional
program, or you can use one of these built-in programs:
or .
5. When you’re saving an HTML file, what should be at the
end of your file name?
6. What program do you need to use to view a website?
492
Which statement is true about spacing?
A. Spacing in HTML is required as part of how the
code runs.
B. Spacing in HTML, like indenting elements, helps the
programmer read their code, but doesn’t impact how
the code is run.
HTML-controls layout
CSS-controls design
36
Chapter
HTML TEXT
ELEMENTS
HEADING ELEMENTS
Websites use headings to divide the text and act as titles
HEADING ELEMENTS
for each section. make text bigger
and bolder.
darker
There are 6 heading tags:
FOR EXAMPLE,
an
, is used to make
paragraphs. HTML ignores all spaces and new lines in code,
so if you want text to appear as its own paragraph, use the
element.
You can also use the element to make text bold
or the element to make text italic.
498
FOR EXAMPLE,
you can surround some content with
tags, specific text with tags to make it bold, and
tags to make it italic:
PARAGRAPH BOLD
A famous example of a shield volcano is Kīlauea
in Hawaii. Kīlauea is still active and adds to the
land mass of the island.
You can add an
A famous example of a shield volcano is Kīlauea
in Hawaii. Kīlauea is still active and adds to the
land mass of the island.
A famous example of a shield volcano is Kīlauea in Hawaii. Kīlauea is still active and adds to the land mass of the island.
Line break element between
and
EMPTY ELEMENTS
Most HTML elements have a start and end tag with content
between them. Some elements have no content and no end
EMPTY ELEMENTS
tag. These are called .
The
LIST ELEMENTS
LIST ELEMENTS
format text as a bulleted or numbered
list. Lists use a combination of elements.
UNORDERED LIST
The
MY FAVORITE FOODS
ELEMENT
FOR EXAMPLE,
to create an unordered list of famous
volcanoes using the
ORDERED LIST
An uses the tag
w
1. What is wrong with the code below?
This is a paragraph
2. What is wrong with the code below?
I like to Move it, Move it
element used?
9. If an element doesn’t have any content or an end tag,
it’s called an .
506
D.
The start tag and end tag must have the
same name.
element is used to set off a chunk of text as its
own paragraph.
The
element creates a line break or a blank line
between elements.
ONCE AGAIN,
I'M ALL
ALONE.
510
37
Chapter
LINK
ELEMENTS
ENGAGING
HYPERLINK
MAKE
IT SO
In HTML, the “hypertext” part of the name means that links
can be used to connect to other pages, websites, or files.
HYPERLINK
A is a connection between websites. A link
turns an HTML element into a button that takes users to
a new website.
511
Links are what make websites useful. Users are able to
instantly jump to related information on other web pages.
For example, when you search for “volcanoes” on a search
engine, you will be given a list of websites that mention
volcanoes. You can click on any of the search results and
jump to the website, because the search engine has added
the links for each site listed.
FACTS AND
TYPES OF
VOLCANOES VOLCANOES
OF THE WORLD
SEARCH ENGINE
VOLCANOES
• VOLCANOES OF THE WORLD
• FACTS AND TYPES OF VOLCANOES
• FAMOUS VOLCANOES
• ACTIVE VOLCANOES
ACTIVE VOLCANOES
FAMOUS
VOLCANOES
512
NAVIGATION MENU
Links also power the on a website. A
navigation menu is a collection of links, each of which leads to
a specific location on a website. Links are what make it possible
to visit each page within the site with a click of a button.
POTATO.COM
HOME RECIPES ABOUT
"Spuds are buds!"
ANCHOR ELEMENT
The , , is used to add links to websites.
In addition to
ANCHORS
putting and
AWEIGH!
around the name of
each link, you need to
add the web address
for the website
where the users
will be sent.
513
ATTRIBUTES ATTRIBUTE
add
Extra information
additional information about
within an element
elements. For example, you
can use an attribute to add
ATTRIBUTES
the website address to a link,
the width and height you want
an image to be, or other
style information. HEIGHT
Attributes are included
inside the start tag and
follow this pattern:
WIDTH
attribute name=“information”
the website you
want to go to
To create a link to another website,
use the href attribute.
Use an anchor element with an href attribute to add a link
to the volcano-related website “www.EruptingVolcanoes.com”:
1.
Name the website you want to visit using <a href=” “>.
2.
Add the web address that will act as the link.
3.
Add the tag to show where the link ends.
514
ATTRIBUTE NAME
Visit Erupting
Volcanoes Site
Additional information
(the website we are
Anchor tags will turn “Visit Erupting
linking to)
Volcanoes Site” into a clickable link.
IMAGE ELEMENTS
Images make websites more interesting and engaging.
IMAGE ELEMENT
The is used to add images to
websites. The element is an empty element, so there
is no end tag.
SRC
The (source) attribute is used to specify the file name
and where an image file is located so that the browser
can find the file and display it on the website. Image files
need to be stored with your website file or referenced from
another website.
515
For example, you can use the web
Don’t worry if the
address of a volcano picture from picture looks too big
or too small—it can
another website to add it to the
always be resized
volcano web page. When viewing a
using CSS later.
website, right-click on the image in
Windows (command click on a Mac)
and select “copy image address” from the menu. This copies
the address where the image is stored. You can use this
address as the value for your src attribute.
The copied image address from another website would be
formatted like this:
“www.eruptingvolcanoes.com/images/volcano1.jpg”
A B C
Images stored with a website are usually kept in files.
Their location is specified in the web address, where the
first part is the website (A). Then a
forward slash and the name of the
folder the image is kept in (B). Then
another slash and the name of the
image with the file extension (C).
516
To link to an image, you’ll first add an element and then
paste the image’s web address into the src attribute value like this:
Paste the image address
Type this in. you copied here.
Link only to pictures you own or that you have been
given permission to use with proper attribution.
IT'S ALWAYS A
GOOD IDEA TO GET
PERMISSION FIRST
BEFORE USING
AN IMAGE.
517
w
1. What do the elements
src
I JUST FEEL
SO CONNECTED TO YOU.
CLICK HERE
BABYSLOTH.COM
522
38
Chapter
STYLING
WITH CSS
CASCADING STYLE SHEETS (CSS)
By itself, HTML makes useful websites, but it isn’t great
CASCADING STYLE
for making good-looking websites.
SHEETS
(CSS) is the language used to add style to HTML
files. CSS describes the color, size, layout, backgrounds, fonts,
and other design features for websites. It also allows you
to style your web page differently
YOU’RE
for different environments (like SO
STYLISH.
handheld devices, laptops, and
desktops) while keeping the HTML
content the same.
523
There are different ways to add CSS to a website:
You can add CSS directly to an HTML file in the head
or as an attribute within each HTML element.
You can make a separate CSS file to store the
information. This makes your code easier to read
and to organize.
MAKING A CSS FILE This is the better way!
To make a new CSS file, use the same editor that you used
to make an HTML file (TextEdit or Notepad). You can name a
CSS file anything, but many programmers save a website’s
CSS file as style.css. For simplicity, save your CSS file in the
same folder as your HTML file.
Creating a CSS Style
STYLES
are made by pairing a
STYLE
SELECTOR DECLARATIONS
with .
A specific change
to how HTML
A selector assigns the style to a content looks
particular element in the HTML file.
The selector is the name of the element
without the <> brackets.
524
A declaration is the change in appearance. For example, you
can make text purple or put borders around images.
Selector = elements to be styled
Declaration = what the new style should look like
Add curly brackets around the declaration(s). Add an indent
for each declaration to keep the code clean. Like HTML, CSS
doesn’t pay attention to white space. If you deleted all the
spaces and indents, the code would run the same.
FOR EXAMPLE,
you could type this code into a .css file
to change all the
Formatting the style with the declaration indented
on a separate line and with the closing curly bracket
on the bottom line is only a suggestion to help the
programmer read the text more easily. The programmer
could write all the code on a single line like this
h1{color:blue;} and the computer would read it the same.
Linking Your CSS and HTML Files
Before the new styles from a CSS file can be applied to a
website, the files need to be linked. You can apply the styles
in a CSS file to an
HTML website by HI! HI!
adding an element to
the head of the HTML.
HTML CSS
The link element needs
three attributes:
1.
REL ATTRIBUTE
The stands for “relationship” and
tells what the relationship is to the file you are linking in
the element. When the value is “stylesheet,” you’re
telling the browser that you want the referenced file to
be used as the CSS style sheet for the website.
a template that shows
style and layout settings
526
2.
TYPE ATTRIBUTE
The says what type of file it is-
for example a text/CSS file.
3.
HREF ATTRIBUTE
The identifies the name and
location of the CSS file. If the CSS file is in the same
location as the HTML file, then you just need to add the
file name.
This is the format to link “style.css” to an HTML file using the
link element:
rel attribute
href attribute: Name
of the CSS file
type attribute: Specifies this as a CSS file
Sometimes programmers store their CSS files in a separate
folder (usually called “css”) on their website’s server. If you
do this, add the folder name and a forward slash to the
href value like this:
folder name
527
This element, with all its attributes, tells the web
browser to find the file “style.css” and apply the styles
from that file to this HTML document.
After linking a CSS file to an HTML file, any changes made
to the CSS will change how the website is displayed when
the browser is refreshed.
CSS COLOR ATTRIBUTES
There are three properties that you can use in a style to
change the color of a web page.
Color changes the color of
the text within an element.
Background changes the
background color of the
space that the element takes
up. For example, setting the
background color of the
element to gray will
turn the entire page gray,
but turning the background
of a
element pink will
only turn the background of
the paragraph pink.
528
Border color changes the color
of the border if an element has
a border. If there is no border,
this style will do nothing.
There are a few different ways
to specify a color using CSS:
color names
HEX
RGB
Color Names
COLOR NAMES
is a set of 147 colors that have been given
specific names and can be used in CSS.
Using named colors is convenient because you don’t have
to memorize or look up color codes. But it can be limiting
because there are only 147 colors.
FOR EXAMPLE,
you can use the named color “red” as a
value for a color property to represent pure red.
Format color references like this: property: value;
PROPERTY
color: red; VALUE (THE NAMED COLOR: RED)
529
Examples of color names:
Tomato Orange DodgerBlue
Medium SeaGreen
Gray SlateBlue Violet LightGray
FOR EXAMPLE,
you can make an
530
RGB
RGB
stands for “red, green, blue” and is another type of
code for representing the same colors that HEX does. RGB
code uses three values (numbers 0-255) to say how much red,
green, or blue is in the color. The number 0 means there is no
color, and the number 255 means there is the highest amount
of that color.
The first value in the code represents the amount of red,
the second value is for green, and the third value represents
blue: (red, green, blue).
FOR EXAMPLE,
the code below represents pure red:
Start with “rgb” and surround code with parentheses.
Amount of
rgb(255,0,0)
blue: 0
Amount of Amount of
red: 255 green: 0
The value shows that the highest amount of red is present
in the color, with zero amounts of green or blue.
531
Here’s what it would look like to set the background color to
the same shade of light gray using the color name, HEX, and
RGB values (all these styles would produce the same results):
| body { | body { | body { | |
| ------------ | ------------ | ------------------- | --- |
| background: | background: | background: | |
| lightgray; | #D3D3D3; | rgb(211, 211, 211); | |
| } | } | } | |
| Color name | HEX colors | | RGB |
You don’t need to stick with one way of representing colors
in your website. You can switch between color names,
HEX colors, and RGB colors all within the same file.
| | Color RGB | | |
| --- | ----------- | --- | --- |
name
RGB
HEX
Color RGB
name
532
ELEMENT-SPECIFIC
PROPERTIES
Some elements, like tables and lists, have properties that are
used only for their element (unlike general color properties).
FOR EXAMPLE,
you can change the bullet style of an
unordered list using the list-style-type property along
with one of the specified values shown below:
This is the default
disc square
circle none ( no bullet point is
displayed, just the text)
If you wanted to display an unordered list using squares
instead of the discs, you could insert the CSS code into
your style sheet that selects the
Most programmers don’t memorize all the properties and
values associated with every element available in HTML.
You can look up CSS properties and values on the internet.
COMMENTS
Comments in CSS
Comments keep your styles are ignored by
computers.
organized so that when the CSS
document becomes longer, it’s easy
to locate different pieces of code.
In CSS, comments start with /* and end with / .
FOR EXAMPLE,
you can add a comment in a CSS file
labeling “Heading styles” like this:
/ Heading styles */ comment
h1 {
color: tomato;
}
h2 {
color: #D3D3D3;
}
534
w
1. What does CSS stand for?
2. What are two ways that you can use CSS with your
HTML code?
3. What is CSS used for?
4. Comments in CSS start and end with .
5. What CSS code would you write to make an entire
website’s background violet?
6. The code below has a bug in it. What needs to be added
to fix it?
h1
color: gray;
}
More questions 535
Cascading style sheets
The selector is used to specify which elements the style
should apply to. For example, a style with the “p” selector
will apply to all
elements.
39
Chapter
STYLING
INDIVIDUAL
ELEMENTS
WITH CSS
IDENTIFYING AN ELEMENT
ID (IDENTIFIER) SELECTORS
are like name tags-they
identify a specific element and apply CSS styling to it. An id
name within a CSS document says, “This style applies only to
the element with this id.”
539
STELLA, THIS CSS STYLE
SAYS ONLY YOU GET TO
BE PAINTED PINK.
STELLA CSS
When using id attributes, you must work in both the CSS
and the HTML documents.
CSS Id Selector
You can create an id selector for a CSS style that will be
applied to a specific element in an HTML file. Instead of
using the element name, like “p,” as the selector for the
new style, type “#” and an id name. The id name can be
anything you want, but no
px stands for pixel and is one
spaces are allowed. You can
of the ways of measuring font
make an id selector called
(type) size. The standard
“introduction” and assign it font size on websites is
16 px, which is the same size
a style that has a font size of
as the 12-point font
PIXELS
18 like this:
in Microsoft Word.
font-size: 18px;
}
540
A pixel (px) is also the smallest point of light on a screen.
If you look very closely at
a screen, you can see tiny
dots. Each one of those dots
is a pixel. Step back from
the screen and all the dots
blend together to make a
clear image.
HTML Id Attribute
Attributes are added to tags to give the computer more
information about the element. Use the id attribute to
identify the element you want to style with the CSS code
you added to the CSS file. For example, you can insert an
id attribute called “introduction” to identify a
element
within the web page:
Add this code here to the opening
tag.
Oh, hello there! . . .
element will
now be styled according to the #introduction style created
in CSS, and the font size for “Oh, hello there! . . .” will be set
to 18 px when displayed on the website.
541
THE CLASS SELECTOR
CLASS SELECTOR
The is used to style a group of
elements. The class selector identifies multiple elements
and applies the same style to all of them.
When using the class selector, you must work in both the
CSS and the HTML documents. For example, you can use
the class selector to make the text blue in two of the three
paragraphs in a website.
ART SHE’S NOT LAB
IN OUR
CLASS.
542
CSS Class Selector
To create a class selector for a CSS style, type a period (.)
and a class name. The class name can be anything you
want, but no spaces are allowed. You can make a class
selector called “overview” and assign it a style where the
text color is blue:
.overview {
color: blue;
}
HTML Class Attribute
You can add a class attribute to specific
elements by
typing class= and the class name.
FOR EXAMPLE,
you can insert a class called “overview” to
identify two
elements within the page:
Add this code to the opening
tag.
These two
paragraphs
will display
Oh, hello there! . . .
in blueOn this site we . . .
To learn more about . . .
Classes can be added to multiple elements, even if the
elements are not the same type. You could also add the class
to headings and it would turn the heading blue:
Add the class attribute
and “overview” value.
FOR EXAMPLE,
if you have an image that is 100 px wide
and 200 px tall,
and you set the
LOOKS LIKE
WHAT I LEARNED IN
width to 200 px
MATH CLASS ABOUT
wide, the height RATIOS MAY COME
IN HANDY .
will automatically
scale to 400 px
tall because the
width of this
image is half
of its height.
To set an image on a website to 175 px wide, add this code
to the CSS file:
img {
width: 175px;
}
You can also size an image by percentage in relation to the
size of the element block it is displayed in.
545
FOR EXAMPLE,
you can set an image on a website to
50 percent (or half) the size of the element block using this code:
img {
width: 50%;
}
BORDERS, MARGINS, AND
PADDING
You can use CSS to add space around images.
Borders add a colored frame around all elements including
images, paragraphs, headings, and lists.
Margins and padding add blank space around an
element. Padding is the space between the element’s content
and its border. The margin is the space between the border
and the rest of the website.
MARGIN
BORDER
PADDING
CONTENT
546
You can add a margin to an element using the margin
property in CSS.
FOR EXAMPLE,
you can give an image a 10-pixel margin
by adding the “margin” property value and “10px” as its
value:
Selects all images in the HTML document
img {
margin: 10px;
}
Adds the margin
Some properties, like the border property, are special
because you can add more than one value in the same
declaration.
For example, add “6px solid orange” as the values to make
the borders 6 px thick, solid lines, and orange:
img { Insert a semicolon
at the end of each
border: 6px solid orange;
declaration.
}
547
To create a style that includes the margin, border, padding,
and width of an image, you can combine all the declarations
using a single img selector, with each new declaration on a
new line:
img {
margin: 10px;
border: 6px solid orange;
padding: 20px;
width: 50%;
}
The style will set all elements to have a margin of
10 px, a solid border that’s 6 px wide and orange, a padding
of 20 px, and a width of 50 percent of the width of the
browser window.
The declaration could also be written as img {margin: 10px;
border: 6px solid orange; padding: 20px; width: 50%;}. The indents
and separate lines make it easier for the programmer to read.
548
w
1. What’s the difference between the id selector and the
class selector in CSS?
2. Px stands for .
3. Id selectors in CSS always begin with what symbol?
4. In CSS, class selectors have a before the
class name.
5. If you want to change the size of a picture, which
CSS properties should you use?
6. Which provides space between the element content and
the border: margin or padding?
7. Refer to the table on the next page to answer questions
7A-D.
A. What code should you add to make the
element
with the content “Good Luck!” display in tomato red
text? Where should you add it and in which file?
More questions 549
| HTML FILE: | CSS FILE: | |
|---|---|---|
| “INDEX.HTML” | “STYLE.CSS” | |
| <!DOCTYPE | html> | #redText { |
color: tomato;
| | | } |
| ------------------------ | --- | ------------------ |
| | | li { |
| Test Prep | | font-size: 24px; |
| <link rel="stylesheet" | | } |
| type="text/css" | | .border { |
| href="style.css"> | | border: 2px solid |
| | | gray; |
| | | } |
Things to remember:
Good Luck!
B. What code should you use to add a 2 px solid gray
border to both the
element
of the HTML file like this:
Good Luck!
B.
You should add class=“border” to the
Things to remember:
Good Luck!
554
Index
555555
SYMBOLS
= assignment operator, 151
+ addition operator, 342-343, 357
- subtraction operator, 357
* multiplication operator, 357
\ division operator, 357
== is equal to operator, 168, 170, 376-377, 403
is greater than operator, 168, 376-377, 403
= i s greater than or equal to operator, 168,
376-377, 403hashtag, 50, 316, 530, 540
< is less than operator, 168, 376-377, 403
<= i s less than or equal to operator, 168,
376-377, 403
!+ is not equal to, 168, 376-377, 403
% modulus, 357
** exponential, 357
// floor division, 357
556
INDEX
A attributions, 101-103
abacus, 13 authentication, 464-465
abstraction, 141, 143 authorized access, 463-466
access, authorized, 463-466
access control, 465 B
accessibility, 90 Babbage, Charles, 115
“Accessibility” settings, 30 backdrops, 216, 276
adding lists, 371 back-end languages, 122-123
addition, string, 342-345 background, 528
age-appropriate content, 90 backpack area, 206-207
algebraic expressions, 155 bar graphs, 62
algorithm design, 141, 143 base 2, 126
algorithms base 10, 126
about, 110-111 basic algorithms, 223-246
basic, 223-246 basic conditional statements, 284
creating, 133-135 basic loops, 278-280
definition of, 6 Berners-Lee, Tim, 448
description of, 6-7 beta testing, 91-92
studying, 111-112 binary code
using, 110-120 about, 123-125
alpha testing, 91 description of, 48
American Standard Code for Information representing letters using, 130
Interchange (ASCII), 130 representing numbers using, 126-129
analysis, description of, 8 bitmap mode, 211
Analytical Engine, 115-116 bits, 131
anchor elements, 513-515 black hat hackers, 470
AND statements, 171-174, 288, 407, 409-410 blank lines, printing, 340
animating a cat, 225-232 blind users, 30-31
append function, 369, 372 blocks
Apple II, 15 about, 200-207
application/application software (apps), 17, for animating a cat, 225-232
21. See also programs; software Boolean, 254, 256-259, 279, 284, 287-288
Arduinos, 72 broadcast, 276-277
arrays, 157, 247 C blocks, 274, 278-283
artificial intelligence (AI) programs, 42, cap blocks, 274
140-141 clone, 293
assigning values, 324-325 control, 273-274, 291-293
assignment operators, 151 event, 224, 275-277, 289-290
attacks, 470-475 extensions for, 217-218
attributes glide, 230-232
about, 514-515 go to, 231
color, 528-532 hat, 224-225
href, 514-515, 527 looks, 237-239
id, 541 making your own, 299-302
rel, 526 math, 254-255
src, 515-517 motion, 215, 234-236
type, 527 My Blocks, 306
557
nesting, 258, 278 about, 481-482, 523-524
operators, 254-259, 263-265 class selector in, 543
pen, 229, 242-243 color attributes in, 528-532
procedure, 299-302 colors in, 50
procedure call stack, 300 comments in, 534
repeat, 273 element-specific properties in,
reporter, 247-251, 254, 263-265 533-534
running, 223-224 id selector in, 540-541
sensing, 266-268 linking HTML files and, 526-528
sound, 240-241 making file for, 524-528
stack, 224 styling individual elements with,
turn, 228-229 539-553
types of, 224-225 cat, animating, 225-232
variables in, 247-253, 260-263 CDs (compact discs), 13, 18
blocks menu, 202-203 census data, 61
body of function, 431 central processing unit (CPU), 18-19
element, 486-487 charts, 61, 63
BOMBE, 469 ciphers, 467-469
Boolean, George, 157 citations, 103
Boolean blocks, 254, 256-259, 279, 284, class selector, 541-544
287-288 clone blocks, 293
Boolean values/expressions cloning, 303-305
about, 156-157, 247 code
comparison operators in, 168-171 definition of, 46
in compound conditional statements, how computers read, 123-132
407-411 HTML, 481-483, 484, 488-490
in conditional statements, 403 machine, 124-125
in Python, 323-324, 374-377 in Python, 314-315
border color, 529 reusing, 191-196
borders, 546-548 coding, early days of, 115-116
broadcast blocks, 276-277 collaborating, 97-108
brute force attacks, 470-471 color attributes, CSS, 528-532
build step, as part of engineering design color coding, in Python, 317
process, 71 color names, CSS, 529-532
built-in variables, 250-251 colors
bytes, 131-132 encoding, 48-51
representing, 51
C Colossus Mark 1, 14
C blocks, 274, 278-283 command-line interface (CLI), 30
C++, uses for, 122-123 commenting out, 82
Caesar cipher, 468-469 comments
calculations about, 81-83
with number variables, 351-352 attributions in, 101-102
operators for, 254-259 in CSS, 534
calling a function, 315, 430-431 in HTML code, 490
calling procedures, 193-194, 300 in Python, 315-316
camel case (mixed case), 329 in Scratch, 205
cap blocks, 274 community, getting help from, 101-102
capitalization, 315 comparison operators, 168-170, 256-259,
capitalize function, 347 376-377
cascading style sheets (CSS), 523-538 compilers, 125
558
compiling, definition of, 124 creators, 4
compound conditional statements, 171-174, credit, 101-102
285-288, 407-411 cryptography, 466-469
computable responses, 58 CSS. See cascading style sheets (CSS)
computational thinking, 139-146 cybersecurity, 463-479
computer, definition of, 2
computer networks, 444-447 D
computer science data
concept areas of, 6-9 about, 43-46
description of, 2-12 definition of, 8
computer scientists, work of, 4 description of, 8
computer systems, designing, 68-72 encoding, 47-51
computer technology, uses of, 3 information flow and, 19-20
computers types of, 323-324
description of, 13-27 using, 61-63
human-computer interaction, 29-37 data encoding schemes, 47-48
impacts of, 9 deaf users, 30-31
as information processors, 41 debugging programs
interacting with, 29-37 commenting out and, 82
parts of, 16-23 description of, 31, 32
reading code and, 123-132 in Scratch, 233
through time, 14-15 declarations, 524-526
computing systems declaring procedures, 191-193
definition of, 2 declaring variables, 150
description of, 6 decoding information, 47
conditional statements, 163-178 decomposition, 141-142
about, 163-167 decryption, 467-469
basic, 284 defensive programming, 73-76
comparison operators in, 168-170 defining a function, 430
compound, 171-174, 285-288, 407-411 diagrams for troubleshooting, 32
elif statements, 405-406 distributed denial-of-service (DDoS)
else if statements, 165-166, 174 attacks, 475
else statements, 165, 404-405 documenting, 81-88
nested, 174-175, 285-288, 411-414 domain name system (DNS) servers, 455-456
in procedures, 302 double quotation marks, 316
in Python, 403-422 downloading information, 449-450
in Scratch, 283-288 drivers, 100
while loops, 181, 393-397
conditionals (C blocks), 274 E
consumers, 4 editor window, 311, 313
content efficiency, algorithms and, 111-112
age-appropriate, 90 efficient, definition of, 57
of websites, 484 electrical circuits, 123
control blocks, 273-274, 291-293 elements
convert function, 433-435 about, 484-486
costume list, 210 anchor, 513-515
costumes, 209-210, 237-239 , 486-487
countdowns, 386 in cascading style sheets (CSS), 533-534,
counter variables, 381-386 539-553
cracking a code or cipher, 468 empty, 502
creating a web page, 481-496 formatting, 498-499
559
, 486-487 creating algorithms and, 133-135
heading, 497-498 else if statements in, 167
height of, 544-546 else statements in, 165
HTML text, 497-509 if . . . then statements in, 164
, 486 logical operators in, 172-173
identifying, 539-541 nested conditionals in, 175
image, 515-517 for three-letter word game, 412
link, 511-521 for loops, 180, 381-392
list, 503-505 forever loops, 278, 281
list item, 503-504 formatting elements, 498-499
paragraph, 498-499 formatting for loops, 381
unordered list, 503-504 formatting HTML, 488-490
website, 486-487 formatting strings, 338-340
of websites, 486-487 formatting variable names, 328-329
width of, 544-546 404 Not Found code (status code), 453
elif statements, 405-406 front-end languages, 122
else if statements, 165-166, 174 functions
else statements, 165, 404-405 append, 369, 372
empty elements, 502 body of, 431
encoding colors, 48-51 calling, 315, 430-431
encoding data, 47-51 capitalize, 347
encryption, 467-469 convert, 433-435
engineering defining, 430
definition of, 68 definition of, 192
everyday, 72 float, 355
engineering design process, 68-71 input, 344-345
ENIAC, 14-15 insert, 369-370, 372
Enigma, 469 int, 354
equal signs, 151 len, 371, 372
escaping a character, 338-339 lists and, 367-372
ethernet, 445-446 lower, 346-347
event blocks, 224, 275-277, 289-290 premade, 103
event handlers, 188 print, 314-315, 334-337, 367-368
events, 187-190 procedures and, 423
expectations, setting clear, 98 in Python, 311, 314-315, 423-442
expressions, mathematical, 356-357 range, 382-388
extension remove, 370, 372
.html, 482-483 reverse, 370-371, 372
.py, 313 sort, 370, 372
extensions, 217 string, 345-347
external actions, 188 swapcase, 347
turtle art, 428-429
f turtle graphics, 423-429
Facebook, programming languages for, 122 upper, 347
feedback, incorporating, 89-96
files, saving, 313 g
float function, 355 game developers, 21
floats, 352, 354-355 gigabytes, 132
flowcharts glide block, 230-232
comparison operators in, 169-170 go to block, 231
for conditional statements, 406 graphical user interface (GUI), 30
560
graphics processing unit (GPU), 19 if then statements, 283
graphs, 61-62 if then else statements, 283
grid system, 214-215 image editor, 211
image elements, 515-517
h images
hackers, 469-470 borders, margins, and padding for,
hacktivists, 470 546-548
hardware resizing, 544-546
closer look at, 17-20 impacts of computing, description of, 9
description of, 16 improve the solution, 71
as part of computing systems, 23 incorporating feedback, 89-96
hat blocks, 224-225 indentation, 383, 488
element, 486-487 index, 366
heading elements, 497-498 infinite loops, 395-397
height of elements, 544-546 information
hexadecimal (HEX) color notation, 48, 49-50, collecting and using, 57-66
51, 530, 532 data and, 44-45
Hollerith Tabulating Machine, 61 decoding, 47
Hopper, Grace, 125 definition of, 45
horizontal rules, 499-501 downloading, 449-450
hosts, 452 Information Age, 40-41
href attribute, 514-515, 527 information processors, 41
HTML code, 481-483, 484, 488-490 inner lists, 372-373
.html extension, 482-483 input
HTML files, 452, 526-528 description of, 17
HTML text elements, 497-509 information flow and, 19-20
element, 486 user, 250-251, 344-345, 432-437
Hubble Space Telescope, 132 input data, 44, 46
human-computer interaction, 29-37 input function, 344-345
hyperlinks, 511-512 insert function, 369-370, 372
hypertext markup language (HTML) int function, 354
basic web pages and, 481-483 integers, 352-354
class selector in, 543-544 internal actions, 188
definition of, 448, 481 internet, 444-462
description of, 452 about, 447-449
extension for, 482 description of, 8-9
formatting, 488-490 sending information over, 449-450
id attribute, 541 surfing web and, 451-458
web browsers and, 484 web versus, 451
hypertext transfer protocol (HTTP), 448, 453 internet service providers, 450
hypertext transfer protocol secure (HTTPS), interviews, 58
453 iOS, 22
IP address, 449-450, 455
i IP-internet protocol, 449
id (identifier) selectors, 539-541
identifiers, 148-149, 152-153, 324 j
identifying an element, 539-541 JavaScript
IDLE (integrated development environment interactivity and, 482
program), 311 uses for, 122
if . . . then statements, 163-167 Julius Caesar, 468
561
k basic, 278-280
key words in Python, 326 forever loops, 278, 281
keys, 467 infinite, 395-397
kilobytes, 132 for loops, 180, 381-392
nested, 182-183, 280-283, 397
l in Python, 381-401
languages repeat loops, 278-279, 281-283
back-end, 122-123 repeat until loops, 278-279
front-end, 122 in Scratch, 274, 278-283
JavaScript, 122, 482 while loops, 181, 393-397
natural, 140 Lovelace, Ada, 115-117
PHP, 122, 482 lower function, 346-347
See also hypertext markup language lowercase_and_underscores, 328
(HTML); programming languages
len function, 371, 372 m
libraries, 103, 423 MAC (Media Access Control), 449
lidar, 42 machine code, 124-125
line breaks, 499-501 Makey Makeys, 72
line graphs, 62 making your own blocks, 299-302
linear scale questions, 60 malware, 472
link elements, 511-521 map apps, 41
list elements, 503-505 margins, 546-548
list item element, 503-504 math blocks, 254-255
lists mathematical expressions, 356-357
about, 365 megabytes, 132
adding, 371 micro:bits, 72
changing properties of, 533 mixed case (camel case), 329
functions and, 367-372 mobile applications, programming
HTML text and, 503-505 languages for, 121
inner, 372-373 mobile developers, 21
list elements, 503-505 modules, 423-424
list item element, 503-504 Morse code, 47
for loops and, 387-388 motion blocks, 215, 234-236
operators and, 371 moving the turtle, 424-427
ordered, 505 multiple-choice questions, 59-60
punctuation for, 365-366 My Blocks, 306
in Python, 323-324, 365-374
replacing values in, 368 n
in Scratch, 251-253 naming conventions, 328-329
sorting, 370-371 naming variables in Python, 325-327
sound, 212 natural language, 140
sprite, 208-209 navigation menus, 513
symbols for, 365 navigators, 100
symbols for inner, 372-373 negative integers, 77
variables and, 157, 247 nested conditional statements, 174-175,
within lists, 372-374 285-288, 411-414
local area networks (LANs), 445 nested loops, 182-183, 280-283, 397
logical operators, 171-174, 258, 407-411 nesting blocks, 258, 278
looks blocks, 237-239 networks, description of, 8-9
loop statements, 179-186 Nexus, 448
loops NOT statements, 173-174, 288, 407, 411
562
number conversions, 355 pixels (picture element), 426, 540-541
number types, 352-355 place values, binary, 127-128
numbers plain text files, for README files, 83
representing using binary, 126-129 plan, as part of engineering design process,
as variables, 323, 351-364 70
numeric values, 155-156 positive integers, 77
premade functions, 103
o print function, 314-315, 334-337, 367-368
observations, 60 printing mathematical expressions, 359
open-ended questions, 59 problem, identifying, 69-70
operating systems, 22 procedure blocks, 299-302
operations, order of, 358-359 procedure call stack block, 300
operators procedures, 191-198
in expressions, 356 calling, 193-194, 300
lists and, 371 conditional statements in, 302
logical, 171-174, 258, 407-411 declaring, 191-193
in Scratch, 254-259, 263-265 functions and, 423
string, 341-347 processing, description of, 18-19
OR statements, 172-173, 288, 407, 409-410 programming
order of operations, 358-359 defensive, 73-76
ordered lists, 505 description of, 6-7
organization, in Python, 315-317 early days of, 115-116
output pair, 100
description of, 20 See also Python; Scratch
information flow and, 20 programming languages, 121-138
in Python, 312 about, 121
return values, 434-437 creating algorithms and, 133-135
output data, 44 description of, 113
how computers read code, 123-132
p using, 122-123
packets, 449, 456 programs
padding, 546-548 algorithms and, 112-114
pair programming, 100 applications versus, 17
paragraph elements, 498-499 definition of, 6
parameter values, 314 as part of computing systems, 6
parameters, 194-196, 226-227, 383, 432-437 See also application/application
paraphrasing, 103 software (apps); software
parentheses, 227, 358-359 prompt, in Python, 311
Pascal case, 329 protocols, 445-446
password checker, 394-395, 397 pseudocode, 133, 182
passwords, cyberattacks and, 470-471 punch cards, 116
pattern recognition, 141, 142 punctuation
PEMDAS (Please Excuse My Dear Aunt being careful with, 315
Sally), 358 for lists, 365-366
pen blocks, 229, 242-243 See also symbols; individual punctuation
personal identification numbers (PINs), 471 marks
phishing, 474-475 .py extension, 313
PHP Python
interactivity and, 482 algorithms and, 113-114
uses for, 122 code in, 314-315
pie charts, 63 color coding in, 317
563
conditional statements in, 403-422 basic algorithms in, 223-246
functions in, 311, 314-315, 423-442 blocks in, 200-207, 215, 217-218
getting started in, 310-321 blocks types in, 234-243, 260-268,
key words in, 326 289-293
lists and Boolean expressions in, 365-380 cloning in, 303-305
for loops in, 381-392 conditional statements in, 283-288
loops in, 381-401 control blocks in, 273-274
numbers as variables in, 351-364 data and operators in, 247-272
organization in, 315-317 debugging strategies for, 233
prompt in, 311 event blocks in, 275-277
reserved words in, 153 getting started in, 200-222
strings in, 333-350 loops in, 278-283
uses for, 122-123 making your own blocks in, 299-302, 306
variables in, 323-332, 351-364 operators in, 254-259, 263-265
while loops and nested loops in, 393-401 reusing scripts in, 299-308
sharing projects in, 217
Q sprites in, 208-216
quotation marks Scratch cat, 225-232
for comments, 316 screen readers, 31
in print function, 335 scripts, 223-246
in strings, 333-334, 338-339 about, 223-224
animating a cat with, 225-232
r debugging strategies for, 233
radar, 42 description of, 203-204
raindrops, 303-305 reusing, 299-308
RAM, 18 storing, 206-207
range function, 382-388 walk, 226-230
ransomware, 472 See also blocks
rational numbers, 77 scripts area, 204
README files, 83-84, 101-102 selectors, 524-526
rel attribute, 526 self-driving cars, 42
remove function, 370, 372 sensing blocks, 266-268
repeat blocks, 273 servers, 452
repeat loops, 278-279, 281-283 shell window, 311-312
repeat until loops, 278-279 single quotation marks, 316, 336
reporter blocks, 247-251, 254, 263-265 slide rules, 14
reserved words, 153 smartphones, 13, 15
return values, 196, 434-437 social engineering, 474-475
reusing scripts, 299-308 social media apps, 41-42, 474-475
reverse function, 370-371, 372 software
RGB color notation, 48, 49, 51, 131, 531-532 closer look at, 21-23
roles, creating clear, 99 description of, 16
Ruby, uses for, 122 as part of computing systems, 23
running blocks, 223-224 system, 22
troubleshooting strategies and, 33
s See also application/application
sandboxing, 466 software (apps); programs
say block, 227 sort function, 370, 372
scanners, 48-49 sorting lists, 370-371
Scratch sound blocks, 240-241
about, 200 sound editor, 212
564
sound list, 212 t
sounds, for sprites, 212 tags, 484-486, 488-489, 497-498
sprite lists, 208-209 team, working on a, 97-99
sprites, 200, 208-216, 225-232 terabytes, 132
spyware, 472 test cases, 74, 75-76
src attribute, 515-517 testing, 71, 73-80, 82
stack blocks, 224 text displays, on multiple lines, 336
stage, 213-216 text editors, 482
start parameter, 383 three-letter word game, 411-414
status code (404 Not Found code), 453 thumbnail images, 208-209
step parameter, 383 timelines, setting realistic, 98
stop parameter, 383 touch screens, 20
storage, description of, 18 Transmission Control Protocol (TCP), 456-457
storing information, 40-55 Traveling Salesperson Problem, 112
storing scripts, 206-207 Trojan horse, 472
strengths, focusing on, 98 troubleshooting
string addition, 342-345 definition of, 31
string functions, 345-347 strategies for, 32-33
string operators, 341-347 See also debugging programs
string values, 263 truth tables, 410-411
strings Turing, Alan, 469
description of, 154 turn block, 228-229
formatting, 338-340 turtle graphics, 423-429
in Python, 323-324, 333-350 Twitter, programming languages for, 122
styles, 524-526 two-factor authentication, 465
styling with CSS, 523-538 type attribute, 527
subroutines, 280-283
surveys, 58-60 u
swapcase function, 347 underscore symbol, 152
symbols Uniform Resource Locator (URL), 454
=, 151 upper function, 347
, 311 usability, 90
backslash, 338 USB flash drives, 18
for Boolean expressions, 403 use cases, 74-75
comparison operators, 168-170, 376 User Datagram Protocol (UDP), 458
for CSS comments, 534 user input, 250-251, 344-345, 432-437
double quotation marks, 316 user interface (UI), 29-31
for HTML comments, 490 user-centered design, 89-91
for inner lists, 372-373
for mathematical operations, 357 v
parentheses, 227, 358-359 values
quotation marks, 316, 333-334, 335, assigning, 324-325
338-339 in expressions, 356
single quotation marks, 316, 336 numeric, 155-156
underscore (_), 152 replacing in lists, 368
syntax, 314, 315 return, 196, 434-437
system software, 22 returning, 196
systematic approach to troubleshooting, variable, 148-151
31-32 variables, 148-162
about, 148-149
565
assigning and naming, 150-153 content of, 484
built-in, 250-251 definition of, 121
calculations with number, 351-352 elements of, 486-487
changing value of string, 337 finding, 454-456
counter, 381-386 programming languages for,
declaring, 150 122
formatting names of, 328-329 tools for writing, 482-483
naming, 325-327 viewing, 483
naming with strings, 334 while loops, 181, 393-397
numbers as, 323, 351-364 white hat hackers, 469-470
parameters, 194-196 wide area networks (WANs), 445
in Python, 323-332, 351-364 width of elements, 544-546
in Scratch, 247-253, 260-263 wi-fi, 446
types of information stored by, 154-157 Windows, 22
See also conditional statements wireless, 445-446
vector mode, 211 workloads, equal, 99
video conference services, 458 World Wide Web
viruses, 464, 473 origin of, 448-449
surfing, 451-458
w using internet to surf, 451-458
walk script, 226-230 See also web pages; websites
web. See World Wide Web worms, 473
web browsers, 483, 484
web developers, 21 x
web pages x- and y-coordinates, 214-215
creating basic, 492-496 xp (experience points), 154
programming languages for, 121
websites y
accessing, 451-453 YouTube, programming languages for,
building blocks of, 481-482 122
566
