Preprocessor

Preprocessor is just the tools for text substitution. Preprocessor instructs the C compiler to do some work or processing which is to be done before compilation. Preprocessor is always start with #.Type of preprocessor are:
1. File Inclusion : #include
2. Macros: #define, #undef
3. Conditional : #if, #ifdef, #ifndef,#else, #elif,#error,#pragma,#endif