Recursion

A recursive function calls itself with a smaller version of the same problem, until it reaches a base case that stops the recursion.

int factorial(int n) {
    if (n <= 1) {
        return 1; // base case
    }
    return n * factorial(n - 1); // recursive case
}

printf("%d\n", factorial(5)); // 120

Each call adds a new frame to the call stack; too many nested calls with no base case in sight (or one that's never reached) exhausts the stack, crashing with a stack overflow.

Common mistakes

• Forgetting the base case entirely, or writing one that's unreachable for some inputs — both lead to infinite recursion.