C Header Files

What is a Header File?

A header file is a file with a .h extension that contains declarations of functions, variables, and macros.

It allows multiple source files to share common code.

#include Directive

The #include directive is used to include header files in your program.

Standard Header Files

C provides many built-in header files.

• stdio.h – input/output
• stdlib.h – memory management
• string.h – string functions

Custom Header Files

You can create your own header files to organize code.

Including Custom Headers

Use double quotes to include your own header files.

Function Declarations

Header files usually contain function declarations (prototypes).

The actual implementation is written in a .c file.

Using the Header in main

Include the header file in your main program to use its functions.

Header Guards

Header guards prevent multiple inclusion of the same file.

Why Use Header Files?

Header files are essential for organizing large programs.

• Separate code into multiple files
• Improve readability
• Enable code reuse

Common Mistakes

Be careful with these:

• Forgetting header guards
• Missing function definitions
• Incorrect include paths

Real-World Structure

A typical C project uses multiple files.

Practice

Create a header file with a function and use it in main.

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