In this article, we examine instructions given to the preprocessor and see how they are used in general. The preprocessor handles your code before the compiler interprets it. If you have been wondering just what the preprocessor is used for, this article explains.
Whence and what art thou, execrable shape?
[John Milton 1608-1674]
The Preprocessor and the Compiler
Before the compiler interprets your code, the preprocessor handles it. Its task is to scan through your code and to look for preprocessor instructions; these can for example be used to replace certain tokens with string or numerical values, or to blank out complete sections of the code before the compiler sees it. You can recognize these instructions from the pound (#) symbol that needs to precede every preprocessor instruction.
We are going to examine these instructions and see how they are used in general. Most probably you have been using at least one of them without giving it much thought: 
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