Table of contents
- Preface
- General background information
- Preview
-
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
- 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 (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 their parents and teacherswhere appropriate.
The purpose of this module is to teach you how to write a Scratch program that uses the relational operators shown below:
<(less than)
= (equal to)>(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 . Project Relational01 at startup.
- Image 2 . Project Relational01 output.
- Image 3 . Reduced screen shot of program Relational01 programming interface.
- Image 4 . Full size view of the programming panel for Relational01.
- Image 5 . Starting to use an if-else block.
- Image 6 . Green blocks exposed by clicking the Operators button.
- Image 7 . Intermediate stage in construction of if-else script.
- Image 8 . Screen shot of the output from the program named Relational01.
- Image 9 . 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 that 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.