Because the preprocessor provides simple programming-like commands, it becomes very tempting to use it as a programming language. However, because it is merely a simple macro processor that does not understand syntax, the results of its output can be very misleading, resulting in code that compiles but behaves unpredictably.
There are circumstances where using the preprocessor in complicated ways is warranted. Those are, however, circumstances that require advanced programming techniques and rigorous verification methods that are outside the scope of this book. It is for this reason that I recommend keeping our use of the preprocessor both as simple and as useful as possible.