Before a C program is compiled in a compiler, source code is processed by a program called preprocessor. This process is called preprocessing.
Commands used in preprocessor are called preprocessor directives and they begin with ”#” symbol. Below is the list of preprocessor directives that C language offers.
This macro defines constant value and can be any of the basic data types.
2 Header file inclusion
The source code of the file ”file_name” is included in the main program at the specified place
3 Conditional compilation
#ifdef, #endif, #if, #else, #ifndef
Set of commands are included or excluded in source program before compilation with respect to the condition
4 Other directives
#undef is used to undefine a defined macro variable.
#Pragma is used to call a function before and after main function in a C program