CS 361

Program Development Planning

(by Allen Downey, modified by Dale Skrien)

Some of you may have trouble getting programs constructed efficiently and correctly. Here's some ideas to help you. The key idea is to identify intermediate steps between what you have and what you want.  Each step should be a small change from its predecessor and should be thoroughly tested before the next step is made. Ideally, you shouldn't add more than a few lines of code at a time.

For example:

• add code that tests the basic function of a new feature
• add code that implements a simple new feature
• encapsulate existing code in a new method and invoke it
• generalize existing code by replacing constants with variables
• make syntactic transformations (e.g., from a for loop to a while loop)

Then the important part: Compile, run, and debug the program after every change. If you can't get it to compile and run, it is almost always a bad idea to try to move on to something else and come back.

Things to do when you get stuck:

• make dead certain that the code you are looking at is the code you are compiling and running. Development environments can sometimes confuse you as to what is actually being run.
• go away and thing about something else for a while
• go back and "clean up" the code you have that is already working
• analyze the code you have. Add comments enumerating preconditions and invariants. Add code that checks preconditions.

Experiment with different ways of doing the things you are already doing. You might improve the program, you might get insight into the problem, you might solve the problem, or you might make the problem go away altogether.