The C preprocessor is a 'macro processor' which is used automatically
by the C compiler to transform your program before actual
compilation. It is called a macro processor because it allows
you to define 'macros,' which are abbreviations for longer
constructs.

The C preprocessor provides four separate facilities that you can use as
you see fit:

* Inclusion of header files. 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 code, and then the C preprocessor will replace
the macros with their definitions throughout the program.
* Conditional compilation. Using special preprocessing directives,
you can include or exclude parts of the program according to various
conditions.
* Line control. If you use a program to combine or rearrange source files
into an intermediate file which is then compiled, you can use line
control to inform the compiler about where each source line originated.

You should install this package if you are a programmer who is searching for
such a macro processor.