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C Programming Absolute Beginner’s Guide, Third Edition by Dean Miller, Greg Perry

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7. Making Your Programs More Powerful with #include and #define

Two types of lines you see in many C programs are not C commands at all. They are preprocessor directives. A preprocessor directive always begins with a pound sign (#). Preprocessor directives don’t cause anything to happen at runtime (when you run your program). Instead, they work during the compiling of your program.

These preprocessor directives are used most often:

#include

#define

Every sample program you have written so far has used #include. This chapter finally takes the secret out of that mysterious preprocessor directive.

Including Files

#include ...

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