Functions, Recursion, Scope, and Storage Classes

Why Functions Matter

Functions make programs modular, reusable, testable, and easier to understand. Good C programs avoid putting all logic in main. Instead, they divide responsibilities into clear units.

Function Declaration and Definition

#include <stdio.h>

int add(int a, int b);

int main(void) {
    printf("%d\n", add(2, 3));
    return 0;
}

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

The declaration tells the compiler about the function before use. This becomes especially important in multi-file programs.

Call by Value and Addresses

C passes arguments by value. If you want a function to modify a caller variable, you typically pass its address through a pointer.

void increment(int *value) {
    (*value)++;
}

Recursion

int factorial(int n) {
    if (n <= 1) {
        return 1;
    }
    return n * factorial(n - 1);
}

Recursion is elegant for some problems, but students must understand base cases and stack usage carefully.

Scope and Storage Classes

Real-World Usage Snapshot

Functions and storage rules matter in every serious C codebase. Embedded firmware, networking utilities, database internals, and command-line tools all rely on carefully designed modular functions and predictable variable lifetime.