1.3 Scr0330: sequence, selection, and loop in scratch 2.0.

Table of contents

• Preface
  • Viewing tip
    • Images
• General background information
  • What is structured programming?
    • One door in and one door out
    • Nesting of structures is allowed
  • Pseudocode
  • The sequence structure
    • The action elements themselves may be structures
  • The selection structure
    • Test a condition for true or false
    • The action elements themselves may be structures
    • Sometimes no action is required on false
  • The loop structure
    • Perform the test and exit on false
    • Perform some actions and repeat the test on true
    • Each action element may be another structure
    • Need to avoid infinite loops
  • Other possible structures
• Preview
  • Programming interface for the program named IfSimple01
  • Click the green flag or the basketball
• Discussion and sample code
  • Three sprites
  • Program code for the LeftBeachball
    • Adding the blue go to block to the program
    • Coordinate values
    • Behavior of the LeftBeachball
  • Positioning the other beachball
  • The basketball
    • Initializing the position of the basketball
    • Initializing the orientation of the basketball
    • Handling mouse events on the basketball
    • Behavior of the bottom script
    • The selection block
    • Two independent decisions
  • Control structures available in Scratch
    • How do the two if blocks differ?
    • Specifying the condition on which the decision will be based
    • Two groups of programming blocks have the correct shape
    • Will use the touching block
  • Go back and examine the script
    • Conditions have been established - need actions
  • Programming blocks belonging to the Motion group
    • Turn around and face the other way
  • An online version of this program is available
• Run the program
• Student programming project
  • Orthogonal axes in Cartesian coordinates
  • Draw a straight line to the location of the next mouse click
  • A sneak peek at the solution
• Summary
• What's next?
• Resources
• Miscellaneous

Preface

Scratch 2.0 (released May 9, 2013) is the second major version of Scratch to be released during the life of theproduct. Among other things, it features a redesigned editor and website, and allows you to edit projects directly from your web browser.

This module is one in a collection of modules designed to help beginners of all ages (8 and up) learn how to create the code for computer programs using Scratch 2.0 . Information is provided not only for the beginners themselves but also for their parents and teacherswhere appropriate.

The purpose of this module is to teach you about structured programming; the sequence structure, the selection structure, and the loop structure. The module will also teach you how to write a Scratch program that illustrates the selection structure, mouse events, and Cartesian coordinates .

Finally, the module presents a student project by which you can demonstrate your understanding of the concepts learned from studying the module.

Viewing tip

I recommend that you open another copy of this module in a separate browser window and use the following links to easily find and view the imageswhile you are reading about them.