Answer
A header file contains declarations and macro definitions intended for inclusion by preprocessing. • The `#include` directive replaces the directive with the header’s preprocessing tokens. • Standard headers declare library interfaces such as printf and malloc. • Project headers should use guards or `#pragma once` where supported to prevent harmful repeated inclusion.
💡 C Example
#ifndef MATH_HELPERS_H
#define MATH_HELPERS_H
int square(int value);
#endif
⚡ Quick Revision
Headers share declarations and macros between translation units.