Header file is a file that contains function declaration and macro definition for C in-built library functions.
All C standard library functions are declared in many header files which are saved as file_name.h.
We are including these header files in our C program using “#include ” command to make use of the functions those are declared in the header files.
When we include header files in our C program using “#include ” command, all C code of the header files are included in C program. Then, this C program is compiled by compiler and executed.