In this tutorial you will learn about C Language - The Preprocessor, Preprocessor directives, Macros, #define identifier string, Simple macro substitution, Macros as arguments, Nesting of macros, Undefining a macro and File inclusion.
A unique feature of c language is the preprocessor. A program can use the tools provided by preprocessor to make his program easy to read, modify, portable and more efficient.
C Language - The Preprocessor