Recursion

Recursion is the process of repeating code by calling a subroutine from within that same subroutine.

Pseudocode example

function factorial(n: int) -> int
    if n <= 1 then
        return n
    endif
    return n * factorial(n - 1)
endfunction

C example

The same code in the C programming language would look like this:

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

The same C code with iteration

The alternative to using recursion would be to use iteration. This isn't always the best option, so sometimes iteration is a better choice:

int factorial(int n) {
    int result = n;
    for (int i = n-1; i > 1; i--) {
	result *= i;
    }
    return result;
}