Pre Processor

The c preprocessor is a collection of special statements called directives that are executed at the beginning of the compilation process, which permits the insertion of files in to a c program.The commonly used preprocesssors are
1.File inclusion
2.Macro definition
3.Conditional compilation
#define     #endif      #ifdef      #line       #elif       #error     #include   # if

All processors begins with # sign and followed by a directive.Preprocessors are usually appear at the beginning of a program, but it may appear any were in the program