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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. I will provide a brief introduction to the topic of animation. I will also explain the concept of costumes in Scratch. The programs explained in this module will illustrate the use of costumes to implement a crude animation that makes it appear that a cat sprite is walking.

Table of contents

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.

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Source:  OpenStax, Teaching beginners to code. OpenStax CNX. May 27, 2013 Download for free at http://cnx.org/content/col11498/1.20
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