1.9 Scr0390: custom blocks in scratch 2.0

Table of contents

• Preface
  • Viewing tip
    • Images
• Introduction
  • Calculate the square root
    • Oops, need to do it all over again
    • Is there a better way?
    • A programming module provides a better way
  • Library functions
  • Passing parameters
    • Make the function general
    • Pass me the number please
    • Passing parameters
  • Returning values
    • Performing an action
    • Sending back an answer
• Creating your own custom blocks
• Sample programs
  • CustomBlockTest01
    • A global variable
    • The custom block
    • The driver script
    • The program output
  • CustomBlockTest02
    • The custom block
    • The driver script
    • The program output
• Run the programs
• Student programming project
• 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 forcomputer programs using Scratch 2.0 . Information is provided not only for the beginners themselves but also for theirparents and teachers where appropriate.

The purpose of this module is to explain the use of functions, methods, and procedures in other programming languages, and to show you how to accomplishmuch of that using the new custom block feature of Scratch 2.0.

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 . The More Blocks toolbox.
• Image B . Access to Scratch 2.0 math functions.
• Image C . Mathematical functions available in Scratch 2.0.
• Image D . Program code for CustomBlockTest01.
• Image E . Output from CustomBlockTest01.
• Image F . Program code for CustomBlockTest02.

Introduction

Modular programming code (methods, subroutines, functions, procedures, or whatever you choose to call them) have been used in computer programming since the early days of programming. Such coding modules are often called bythese and various other names.

The new ability in Scratch 2.0 to create custom blocks can be used to provide much of the same modular functionality.

Calculate the square root

Suppose that your program needs to calculate the square root of a number.

In case you don't know what it means to compute the square root of a number, don't worry about it. Suffice it to say that it is a fairly complexmathematical process that requires a non-trivial amount of computer program code to accomplish.

Referring back to your high-school algebra book, you could refresh your memory on how to calculate a square root. Then you could construct the algorithmdescribing that process. Having the algorithm available, you could write the code to calculate the square root and insert that code into your program code.Then you run your program.