Define Four Facilities Provided by C Language Preprocessor?
The C language preprocessor provides four separate facilities that you can use as you see fit:
 
- Inclusion of header files and these      are files of declarations that can be substituted into your program.
 
 
- Macro expansion, You can define macros, which      are abbreviations for arbitrary fragments of C language code, and then the      C language preprocessor will replace the macros with their definitions      throughout the program.
 
 
- Conditional compilation. Using extraordinary      preprocessing directives you can exclude or include parts of the program      according to various conditions.
 
 
- Line control. If you use a program      to rearrange or combine source files into an intermediate file which is      then compiled you can use line control to inform the compiler of where      each source line originally came from.