Recursion in C

A base case and a smaller problem, on the stack rather than in a loop.

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

int sum_digits(int n) {
    if (n < 10) {
        return n;
    }
    return n % 10 + sum_digits(n / 10);
}

int ackermann_lite(int m, int n) {
    if (m == 0) {
        return n + 1;
    }
    return ackermann_lite(m - 1, 1);
}

How it works

1. The base case is what stops the recursion.
2. Each call gets its own copy of the locals.
3. Deep recursion costs stack, so C often prefers the loop.

Keywords and builtins used here

• ackermann_lite
• factorial
• if
• int
• return
• sum_digits

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Step 6 of 7 in Functions, step 20 of 35 in Language basics.

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Recursion in other languages

• Python