Cpp 4.1.1 - The C Preprocessor.

Cpp is the GNU C-Compatible Compiler Preprocessor. Cpp 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, abbreviations for longer constructs.

The C preprocessor provides four separate functionalities: the inclusion of header files (files of declarations that can be substituted into your program); macro expansion (you can define macros, and 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); and 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 C programmer and you use macros.