1.7 Scr0370: the repeat loop in scratch 2.0  (Page 8/7)

Table of contents

• Preface
  • Viewing tip
    • Images
• General background information
  • Definite versus indefinite loops
    • A definite loop example
    • Explanation of the definite loop
    • An indefinite loop example
    • Explanation of the indefinite loop
  • The while and for keywords
• Preview
• Discussion and sample code
  • The program named ForLoop01
    • Why set count to 0?
    • Purpose of the pseudocode
    • What's new in this Scratch program?
    • Animation
    • Costumes
    • The cat sprite has two costumes
    • Loop blocks
    • The repeat (numeric value) block
    • Setting the number of repeats (iterations)
    • Can also use a variable
    • The wait block
    • The switch costume block
    • The program code
    • Behavior of the program
    • The repeat block
    • Run the online version
  • The program named ForLoop02
    • The program code
    • Create a variable
    • The initialization code
    • The repeat block
    • The operational difference
  • Online versions of these programs are available
• Run the programs
• Student programming project
• Summary
• What's next?
• Resources
  • General resources
  • Programs used in this series
• Miscellaneous

Preface

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

This module (tutorial) 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 theirparents and teachers where appropriate.

In this module, you will Learn the difference between a definite loop and an indefinite loop . I will explain two Scratch programs that approximate the Scratch equivalent of a for loop in other programming languages. In Scratch, it is called a repeat loop. One of the programs causes a block of code to be executed a fixed number of times when the user clicks the green flag. Theother program causes a block of code to be executed a variable number of times when the user clicks a sprite.

I will provide a brief introduction to the topic of animation. I will also explain the concept of costumes in Scratch. Both of the programs mentioned above will illustrate the use of costumes to implement a crude animationthat makes it appear that a cat sprite is walking.

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.

Images

• Image A . A definite loop for eating cookies.
• Image B . An indefinite loop for eating cookies.
• Image C . Pseudocode for the program named ForLoop01.
• Image D . The costumes tab for a new Scratch project.
• Image E . Various Scratch blocks.
• Image F . Program code for the program named ForLoop01.
• Image G . The cat on the Stage.
• Image H . Program ForLoop02 output after clicking the green flag.
• Image I . Program ForLoop02 output after clicking the cat.
• Image J . Program code for the program named ForLoop02.
• Image K . ForLoop03 output after clicking the green flag.