Preprocessor directives

Preprocessor directives starts with '#' and operate by the preprocessor before the program is compiled. Each preprocessor directives has a different function. #include and #define directives are most commonly used. #include directive is used in the program to include required code for the codes used for functions. For example, we have designed a program and we want to print the output to the screen. For this, we have to use printf function that is a standard function of the C language.

Printf ("Sample Output");

However, in order to run the printf function, we need to have files. To include this file to the program, #include <stdio.h> command line is written to the top of the program. Files with .h extension is called Header File in the C programming language. <stdio.h> header file contains the necessary codes for standard input-output operations.