6. Functions

Function declaration, definition, parameters, return values, and pass-by-value semantics in C.

Functions encapsulate behavior and enable reuse and testing.

• Declaration (prototype) vs definition
• Parameters and return values
• Pass-by-value semantics in C

Examples

Factorial (factorial.c)

A function that computes N! using a loop, demonstrating parameters and return values:

#include <stdio.h>

int main(void) {
    int n;
    printf("Enter N (0..12): ");
    scanf("%d", &n);

    if (n < 0) {
        printf("Factorial not defined for negative numbers.\n");
        return 0;
    }

    unsigned long long fact = 1ULL;
    for (int i = 1; i <= n; i++) {
        fact *= (unsigned long long)i;
    }
    printf("%d! = %llu\n", n, fact);
    return 0;
}

Add Two Numbers (add_two_numbers.c)

A minimal function that takes two parameters and returns their sum:

#include <stdio.h>

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

int main(void) {
    printf("add(3,4) = %d\n", add(3,4));
    return 0;
}