1.8 Scr0380: the forever and repeat until loops in scratch 2.0  (Page 3/7)

Figure

Image i. final screen output from the program named repeatuntil01.

Doesn't have to be the last block in the script

Unlike the forever block, it is possible to connect another block to the bottom of a repeat until block. Therefore, it is not necessary for a repeat until block to be the last block in a script. This means that a program can continue to execute a repeat until block until a specified condition becomes true, and then move on to execute additional code.

This structure is more similar to the structures typically found in modern programming languages than are the structures required by the forever block. However, most modern programming structures repeat something while a condition is true instead of repeating it until a condition becomes true.

Available online

At the real risk of becoming really boring, I will tell you again that you can copy the code from Image H and run your own copy of the program. Also, the program has been posted online so that you can run it from there. (See the link to the online version in Resources .)

The loop blocks

The three blocks shown in Image J are the only blocks available to create loop structures in Scratch version 2.0.

(The forever if block that was available in v1.4 is no longer available in v2.0. However, its functionality can approximated by embedding an if block in a forever block.)

Figure

Image j. blocks that can be used to create loop structures in v2.0.

In this and the previous program, I have provided discussions and sample programs using the three blocks in Image J as well as a discussion and sample program for a forever block with an embedded if block.

Run the programs

I encourage you to use the information provided above to write and run these three programs. Experiment with the code, making changes, and observing theresults of your changes. Make certain that you can explain why your changes behave as they do.

Just for fun, see if you can cause the cat to change color as it marches around in the circle.

I also encourage you to write the program described below.

Student programming project

Write a program named ForeverLoop03 that is very similar to the program named ForeverLoop01 . Once again, the cat marches in a circle when the user holds down the space bar (after first clicking the green flag) . However, this program also produces an audio output that is a nice drumbeat andthe cat marches in synchronism with the drumbeat.

My version of this program has been posted online so that you can run it from there. (See Resources for the link to the online version.)

Because of the speed of my computer and the speed of my Internet connection, the synchronization of the drumbeat and the animation in v2.0 is notas good as it was when running the program locally under v1.4. Losing the ability to run Scratch programs locally is one disadvantage of the changes thatwere made in v2.0.

Summary

In this module, I presented and explained three Scratch programs. One program uses a forever block in conjunction with an embedded if block to cause a sprite to move in a small circle whilethe space bar is pressed. I explained that it is not possible to connect another block to the bottom of a forever block. Therefore, if you use a forever block, it must be the last block in the script in which it is contained.