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I encourage you to use the information provided above to write and run these two 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 add a drumbeat that keeps time as the cat walks.
I also encourage you to write the program described below.
Write a Scratch program named ForLoop03 . This program places a cat sprite, a slider variable, and a button on the stage as shown in Image K . The cat sprite has two costumes.
This program is an upgrade of the program named ForLoop02 , but is more complex than that program. In particular, this program uses the ability of onesprite (the button) to communicate with another sprite (the cat) by broadcasting and receiving messages.
You may have to do some online research to learn how to fire and handle broadcast events. Hint: See the bottom three blocks in the Events toolbox.
When the user clicks the button, this program behaves just like the program named ForLoop02 behaves when the user clicks the cat in that program. (Note, however, that the drawing of axes and lines was omitted from this program for simplicity.)
As in the previous program, this program executes its animation using a repeat block. Also as in the previous program, the number of times that the code in the repeat block is executed is specified by the current position of the slider.
A copy of this program has been posted online for your review (see Resources for the URL) . If you don't find the program using that URL, search the Scratch site for the usernamed dbal.
I began by providing a real-world example of the difference between a definite loop and an indefinite loop.
Then I presented and explained two Scratch programs that illustrate the Scratch equivalent of (or something similar to) a for loop in other programming languages. In Scratch, it is called a repeat loop. One of the programs caused a block of code to be executed a fixed number of times when the user clicked the greenflag. The other program caused a block of code to be executed a variable number of times when the user clicked a sprite.
I provided a brief introduction to the topic of animation and I explained the concept of costumes in Scratch. Both programs illustrate the use of costumes to implement crude animation that makes it appear that a cat sprite iswalking.
I also provided a student programming project.
The next module will concentrate on other variations of Scratch loops.
This section contains a variety of miscellaneous information.
Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.
I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.
In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. Ineither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please beaware that it is a copy of a module that is freely available on cnx.org and that it was made and published withoutmy prior knowledge.
Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.
-end-
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