Scratch Programming for Teens

337 Pages·2008·7.11 MB·English

by  Jr. Jerry Lee Ford

Scratchtm
Programming
for Teens
Jerry Lee Ford, Jr.
Course Technology PTR
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To my mother and father for always being there, and to my wonderful children,
Alexander, William, and Molly, and my beautiful wife, Mary.
Acknowledgments
ThereareanumberofindividualstowhomIowemanythanksfortheirhelpand
assistance in the development of this book. For starters I need to thank Mitzi
Koontzwhoservedasthebook’sacquisitionseditor.Specialthanksalsogooutto
Jenny Davidson for serving as the book’s project editor. I also want to thank
Parker Hiquet and Hannah Wittig for all the valuable input and advice. In
addition, I would like to thank everyone else at Cengage Learning for all their
hard work.
Special thanks to the Scratch development team at the MIT Media Lab for
providing such an excellent programming langauge and website.
About the Author
Jerry Lee Ford, Jr. is an author, educator, and an IT professional with over
18years’experienceininformationtechnology,includingrolesasanautomation
analyst, technical manager, technical support analyst, automation engineer,
and security analyst. He is the author of 24 other books and co-author of two
additionalbooks.HispublishedworksincludeAppleScriptStudioProgramming
for the Absolute Beginner, Microsoft Windows PowerShell Programming for the
Absolute Beginner, Microsoft Visual Basic 2005 Express Edition Programming for
the Absolute Beginner, Microsoft VBScript ProfessionalProjects,Microsoft Windows
Shell Scripting and WSH Administrator’s Guide, Microsoft Windows Shell Script
Programming for the Absolute Beginner, Learn JavaScript in a Weekend, Second
Edition,andMicrosoftWindowsXPProfessionalAdministrator’sGuide.Jerryhas
a master’s degree in business administration from Virginia Commonwealth
University in Richmond, Virginia, and he has over five years’ experience as an
adjunct instructor teaching networking courses in information technology.
Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiv
PART I SCRATCH BASICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Chapter 1 Introducing Scratch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Getting to Know Scratch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Imagine—Program—Share! . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Scratch Uncovered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Scratch’s Building Block Approach to Programming . . . . . . . . . . 6
Installing Scratch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Installing Java on Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Installing Scratch on Windows . . . . . . . . . . . . . . . . . . . . . . . . . 10
Installing Scratch on Mac OS X. . . . . . . . . . . . . . . . . . . . . . . . . 12
Creating Your First Scratch Application . . . . . . . . . . . . . . . . . . . . . 14
Creating a New Scratch Project . . . . . . . . . . . . . . . . . . . . . . . . 15
Changing Sprite Attributes. . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Adding Code Blocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Saving Your Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Joining Scratch’s Global Community . . . . . . . . . . . . . . . . . . . . . . . 19
Sharing Your Application Projects . . . . . . . . . . . . . . . . . . . . . . 21
Registering with the Scratch Website . . . . . . . . . . . . . . . . . . . . 23
Keeping In Touch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
vi
Contents vii
Chapter 2 Getting Comfortable with the Scratch Development
Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Getting Comfortable with the Scratch IDE. . . . . . . . . . . . . . . . . . . 28
Getting Familiar with Menu Bar Commands . . . . . . . . . . . . . . . 29
Running Scratch Applications on the Stage. . . . . . . . . . . . . . . . 31
Running Applications in Presentation Mode . . . . . . . . . . . . . . . 33
Controlling Application Execution . . . . . . . . . . . . . . . . . . . . . . 33
Working with the Sprite List . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Generating New Sprites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Tracking Mouse Pointer Location . . . . . . . . . . . . . . . . . . . . . . . 36
Working with the Scratch Toolbar . . . . . . . . . . . . . . . . . . . . . . 37
Switching Between Code Block Groups. . . . . . . . . . . . . . . . . . . 38
Getting Comfortable with the Scripts Area . . . . . . . . . . . . . . . . 38
Keeping Project Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Creating New Sprites Using Scratch’s Paint Editor . . . . . . . . . . . . . 46
Examining the Drawing Canvas . . . . . . . . . . . . . . . . . . . . . . . . 46
Working with the Toolbar and Options Area . . . . . . . . . . . . . . 47
Working with Button Controls . . . . . . . . . . . . . . . . . . . . . . . . . 49
Specifying Color Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Configuring a Sprite’s Rotation Center . . . . . . . . . . . . . . . . . . . 50
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Chapter 3 A Review of the Basic Components of Scratch Projects . . 53
Working with Blocks and Stacks . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Three Basic Types of Scratch Blocks . . . . . . . . . . . . . . . . . . . . . . . . 55
Working with Stack Blocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Working with Hat Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Working with Reporter Blocks . . . . . . . . . . . . . . . . . . . . . . . . . 57
Keeping an Eye Out with Monitors . . . . . . . . . . . . . . . . . . . . . . . . 58
Eight Categories of Scratch Blocks. . . . . . . . . . . . . . . . . . . . . . . . . 60
Moving Objects Around the Drawing Canvas . . . . . . . . . . . . . . 61
Changing Object Appearance. . . . . . . . . . . . . . . . . . . . . . . . . . 62
Making Some Noise. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
Drawing Lines and Shapes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Looping, Conditional Logic, and Event Programming . . . . . . . . 65
Sensing Sprite Location and Environmental Input . . . . . . . . . . . 65
Working with Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Storing and Retrieving Data. . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Getting Help with Code Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
viii Contents
Chapter 4 Mr. Wiggly’s Dance—A Quick Scratch Project . . . . . . . . . 73
Programming with Scratch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Creating the Mr. Wiggly’s Dance Application . . . . . . . . . . . . . . . . 75
Step 1: Creating a New Scratch Project . . . . . . . . . . . . . . . . . . . 77
Step 2: Adding a Background to the Stage. . . . . . . . . . . . . . . . 77
Step 3: Adding and Removing Sprites. . . . . . . . . . . . . . . . . . . . 80
Step 4: Adding Mr. Wiggly’s Music. . . . . . . . . . . . . . . . . . . . . . 82
Step 5: Playing the Dance Music. . . . . . . . . . . . . . . . . . . . . . . . 85
Step 6: Making Mr. Wiggly Dance . . . . . . . . . . . . . . . . . . . . . . 87
Step 7: Saving and Executing Your New Scratch Application . . . 90
Distributing Scratch Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Distributing Scratch Applications to Windows Computers . . . . . 92
Distributing Scratch Applications to Mac OS X Computers. . . . . 93
Instructions for Executing Your Application from a CD-ROM. . . 93
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
PART II LEARNING HOW TO WRITE SCRATCH PROGRAMS . . . . . . 95
Chapter 5 Moving Things Around . . . . . . . . . . . . . . . . . . . . . . . . . 97
Working with Motion Code Blocks . . . . . . . . . . . . . . . . . . . . . . . . 98
Moving and Rotating Sprites . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
Setting Sprite Direction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Repositioning a Sprite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Changing Sprite Coordinates. . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Bouncing Sprites Around the Stage. . . . . . . . . . . . . . . . . . . . . . . 105
Keeping Track of Sprite Coordinates and Direction . . . . . . . . . . . 106
Taking Advantage of Scratch Cards . . . . . . . . . . . . . . . . . . . . . . . 107
Creating the Virtual Scratch Fish Tank. . . . . . . . . . . . . . . . . . . . . 110
Step 1: Creating a New Scratch Project . . . . . . . . . . . . . . . . . . 111
Step 2: Adding a Background to the Stage. . . . . . . . . . . . . . . 111
Step 3: Adding and Removing Sprites. . . . . . . . . . . . . . . . . . . 111
Step 4: Adding a Suitable Audio File to the Stage . . . . . . . . . 112
Step 5: Playing the Audio File . . . . . . . . . . . . . . . . . . . . . . . . 113
Step 6: Animating the Swimming of the Fish . . . . . . . . . . . . . 113
Step 7: Saving and Executing Your New Scratch Application . . 116
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Chapter 6 Sensing Sprite Position and Controlling
Environmental Settings . . . . . . . . . . . . . . . . . . . . . . . . 119
Working with Sensing Code Blocks . . . . . . . . . . . . . . . . . . . . . . . 120
Retrieving Mouse Button and Coordinate Status . . . . . . . . . . . . . 121
Determining when Keys Are Pressed . . . . . . . . . . . . . . . . . . . . . . 123
Contents ix
Determining when Sprites Collide with Other Objects . . . . . . . . . 124
Determining Distance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
Working with a Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
Retrieving Stage and Sprite Data . . . . . . . . . . . . . . . . . . . . . . . . 129
Retrieving Audio Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
Code Blocks That Work with Sensor Boards. . . . . . . . . . . . . . . . . 131
Creating the Family Scrapbook Application . . . . . . . . . . . . . . . . . 132
Step 1: Creating a New Scratch Project . . . . . . . . . . . . . . . . . . 132
Step 2: Adding and Removing Sprites and Costumes. . . . . . . . 133
Step 3: Adding a Suitable Audio File to the Stage . . . . . . . . . 134
Step 4: Playing the Audio File . . . . . . . . . . . . . . . . . . . . . . . . 135
Step 5: Displaying the Photographs . . . . . . . . . . . . . . . . . . . . 135
Step 6: Saving and Executing Your New Scratch Application . . 136
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
Chapter 7 Storing and Retrieving Data. . . . . . . . . . . . . . . . . . . . . 139
Learning How to Work with Application Data. . . . . . . . . . . . . . . 139
Storing Data in Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Creating Scratch Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Assigning Variables to Sprites and the Stage . . . . . . . . . . . . . 142
Assigning Names to Your Variables . . . . . . . . . . . . . . . . . . . . 143
Understanding Variable Scope . . . . . . . . . . . . . . . . . . . . . . . . 143
Deleting Variables when They Are No Longer Needed. . . . . . . . . 145
Accessing Variables Belonging to Other Sprites . . . . . . . . . . . . . . 145
Working with Variable Monitors. . . . . . . . . . . . . . . . . . . . . . . . . 147
Two Quick Examples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
Developing the Basketball Quiz Project . . . . . . . . . . . . . . . . . . . . 148
Step 1: Creating a New Scratch Project . . . . . . . . . . . . . . . . . . 150
Step 2: Selecting an Appropriate Stage Background . . . . . . . . 150
Step 3: Adding and Removing Sprites. . . . . . . . . . . . . . . . . . . 150
Step 4: Adding Variables Required by the Application . . . . . . 151
Step 5: Adding Scripts to Button Sprites to Collect
User Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Step 6: Automating the Administration of the Quiz . . . . . . . . 154
Step 7: Saving and Executing Your New Application. . . . . . . . 157
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
Chapter 8 Doing a Little Math . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
Addition, Subtraction, Multiplication, and Division . . . . . . . . . . . 159
Understanding the Mathematical Order of Precedence . . . . . . . . 160
Generating a Random Number . . . . . . . . . . . . . . . . . . . . . . . . . . 161