In this chapter, we used modular programming techniques to implement a hypothetical chart-generation package called Charter. We saw how charts are made up of standard elements, and how this organization can be translated into program code. After successfully creating a working chart-generation library that renders charts as bitmapped images, we saw how a fundamental change in requirements can seem to be a problem at first, but is actually an opportunity to refactor and improve your code.

Following through with this hypothetical example, we refactored the Charter library to handle PDF formatted charts. In doing so, we learned that using modular techniques to respond to a major change in requirements can help to isolate the changes that need to be made, and that refactoring our code often results in a system that is better organized, more expandable and more robust than what we started with.

In the next chapter, we will learn how to use standard modular programming "patterns" to deal with a range of programming challenges.