Last Minute C Programming Preprocessor Directives Tutorial
A Preprocessor in a C programming language is a Program that processes source code of a C program, expanding Macro Definitions, File Inclusions and more.
Only through Preprocessor directives, you are able to include library files in your C program.
Preprocessing in C happens before compilation. Part of the Source code is replaced with Preprocessing expressions where ever encountered. So the size of Total code increases before passing to the Compiler.