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Now it's time to write and discuss a Scratch program. You should be able to replicate this program.
Hopefully by now you have worked your way through the Step-by-Step Intro and the various tips that you can access by clicking the question mark on the right side of your browser window when the window is open on theScratch website's programming interface . (Click the Create link on the Scratch website to open the programming interface . )
Hopefully you have also worked through several of the tutorials that you can find on Scratch as recommendedin the previous module. If not, you should do that before continuing with this module. In other words,by now you should have experience moving Scratch blocks around to cause your sprites to behave as you want them to behave.
In case you skipped the section titled An overview of computer programming , you might still want to go back and review the section on Variables .
Click here to run this program in your browser.
This Scratch program illustrates the creation and manipulation of two simple numeric variables.
Scratch variables can contain numeric values or strings of characters but this program will deal only with numeric values.
This program also illustrates the case sensitivity of variable names along with the ability to detect and respond to events fired by the keyboard andevents fired by the mouse.
A variable named Counter (with an upper-case "C") is created, initialized to 0, and displayed in the upper-left corner of theStage area in the Scratch programming interface (see Image 1 ) . Although the label on this variable is small and difficult to read, you will see when you run this program that this is the topmost variable displayed on the Stage.
When the user clicks the green flag in the upper-right corner of the stage , the value of the variable is set to zero. Each time the userpresses the space bar, the value of the variable is increased by 1. Each time the user clicks the mouse in the blank area of the Stage, the value of thevariable is decreased by 1.
Another variable named counter (with a lower-case "c") is created, initialized to 0, and displayed below the Counter variable on the Stage. Again, when the user clicks the green flag in the upper-right cornerof the stage in Image 1 , the value of the variable is set to zero. Each time the user presses the space bar, the value of thisvariable is increased by 5. Each time the user clicks the mouse in the blank area of the Stage, the value of this variable is decreased by 5.
Image 1 shows a cropped image of the Scratch programming interface for the program named Variable01 for Scratch v2.0.This image was produced by running the program online and clicking the blue button in the upper-right corner labeled See inside .
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