The C preprocessor is a special tool created to facilitate the programming of C applications and expedite their execution. This is an important and, at the same time, confusing thing: the C preprocessor is a wholly separate entity from the C language itself. That being said, most C compilers will manage preprocessing for you, so as long as you abide by the proper syntax and understand how the preprocessor functions, working with it can be a relatively seamless process.
The C preprocessor helps you organize your code by providing utilities for
Creating reusable snippets of code, called macros
Including the contents of one source file during another source file's compilation
Providing additional direction to the ...