2.5 Scr0150: relational operators  (Page 13/6)

Table of contents

• Preface
  • Viewing tip
    • Images
• General background information
  • Operator categories
• Preview
  • Program operation
  • No boolean type available in Scratch
• Discussion and sample code
  • A button and five variables
  • The program code
    • Initialize the variables
    • When the button is clicked...
    • An if-else block
    • Need to put a conditional clause in the pocket
    • Where are the blocks with the correct shape?
    • Will use blocks from the Operators group
    • Six blocks have the correct shape
    • Relational operators in other languages
    • Three steps at once
    • Still need to complete the conditional clause
    • Complete the relational expression
    • Completing the program
  • A screen shot of the program output
  • Interpretation of the results
  • An online version of this program is available
• Run the program
• Student programming project
  • Operation of the program
• Summary
• What's next?
• Resources
  • General resources
  • Programs used in this collection
• Miscellaneous

Preface

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. Information is provided not only for the beginners themselves butalso for their parents and teachers where appropriate.

The purpose of this module is to teach you how to write a Scratch program that uses the following relational operators: less than , equal to , and greater than .

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 images while you are reading about them.

Images

• Image 1 . Reduced screen shot of program Relational01 in operation.
• Image 2 . The center programming panel for Relational01.
• Image 3 . Starting to use an if-else block.
• Image 4 . Green blocks exposed by clicking the Operators button.
• Image 5 . Intermediate stage in construction of if-else script.
• Image 6 . Screen shot of the output from the program named Relational01.
• Image 7 . Screen shot of the output from the program named Relational02.

General background information

First, a quick review of material from earlier modules:

• Operators are the action elements of a computer program. They perform actions such as adding two variables.
• Operands are the things that are operated on by operators. For example, variables are often the operands that are operated on by operators.
• An expression is a specific combination of operators and operands, which evaluates to a particular result.
• A statement is a specific combination of expressions.
• The equal character (=) would commonly be called the assignment operator in programming languages such as Java but we will see later that it is used as a relational operator in Scratch.
• Scratch has two types of data (numeric and string).
• An operator that operates on one operand is called a unary operator.
• An operator that operates on two operands is called a binary operator.
• An operator that operates on three operands is called a ternary operator. Scratch doesn't have any ternary operators.
• Binary operators in Scratch use infix notation. This means that the operator appears between its operands.