Recursive functions

This lesson covers writing a recursive function in Objective-C, with the aim of understanding how a function can call itself.

A recursive function is one that calls itself. It suits work that repeats the same pattern of calculation, such as "n! = n × (n-1)!".

In the sample code, a factorial function calls itself as n * factorial(n - 1) to calculate 5 factorial. The finishing condition if (n <= 1) return 1; is what makes the calls stop somewhere.

A common early stumble is forgetting the finishing condition. Without one, the function calls itself forever and the program dies.

In professional work, deep recursion consumes a great deal of stack, so it is worth considering whether a loop would do instead.

📖 Reference code

NSInteger factorial(NSInteger n) {
    if (n <= 1) return 1;
    return n * factorial(n - 1);
}
NSLog(@"%ld", (long)factorial(5));

✍️ Your code

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🧪 This site can't compile or run Objective-C directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).