Summary of the Design Process

You have just seen an example of top-down design in action. Now you can really see why it's called top-down design. We started at the highest level of our structure chart and worked our way down. At each level, we began with a general algorithm and then gradually refined it into precise code. This approach is sometimes called step-wise refinement. The whole process can be summarized in four steps:

1. Express the algorithm as a series of smaller problems.

2. Develop an interface for each of the small problems.

3. Detail the algorithm by expressing it in terms of its interfaces with the smaller problems.

4. Repeat the process for each smaller problem.

Top-down design is an invaluable tool for developing complex algorithms. The process may seem easy, since I've walked you through it step-by-step. When you first try it out for yourself, though, things probably won't go quite so smoothly. Stay with it—the more you do it, the easier it will get. Initially, you may think writing all of those functions is a lot of trouble. The truth is, developing any sophisticated system is virtually impossible without a modular approach. Keep at it, and soon expressing your own programs in terms of cooperating functions will become second nature.

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