🟡 Intermediate · Lesson 31

Header Files

What are Header Files?

Header files contain function declarations, macro definitions, constants and structure declarations. They usually have a .h extension.

💡 Purpose

Header files help split a large program into smaller reusable files.

calc.h

#ifndef CALC_H
#define CALC_H

int add(int a, int b);
int multiply(int a, int b);

#endif

calc.c

#include "calc.h"

int add(int a, int b) {
    return a + b;
}

int multiply(int a, int b) {
    return a * b;
}

main.c

#include <stdio.h>
#include "calc.h"

int main() {
    printf("Sum = %d\n", add(10, 20));
    printf("Product = %d", multiply(5, 4));
    return 0;
}

Sum = 30 Product = 20

Compile Command

Use: gcc main.c calc.c -o app

Header files में function declarations, macros, constants और structures की declarations रखी जाती हैं। इनका extension सामान्यतः .h होता है।

calc.h

#ifndef CALC_H
#define CALC_H

int add(int a, int b);
int multiply(int a, int b);

#endif

main.c

#include <stdio.h>
#include "calc.h"

int main() {
    printf("%d", add(10, 20));
    return 0;
}

Compile

gcc main.c calc.c -o app