What is #include ?

#include is a preprocessor directive which is used to insert functions and files in the program from the C library. In other word if you want to insert source code file or functions from outside the program than you want to use a #include directive to insert these files or functions,
functions which are included in the program with #include directive is called header files has extension ‘.h’. There are two ways to write #include statement. These are:

1. #include "filename" /* This command would look for the file filename in the current directory as well as the specified list of directories as mentioned in the include search path that might have been set up. */

2. #include <filename> /* This command would look for the file filename in the specified list of directories only. */

Example:

#include “calculator.c”

#include <calculator.c>

#include <stdio.h>