A recursive algorithm for computing gcd$($a$,$b$)$

Procedure gcd$($a$,$b: nonnegative integers with a $<$ b$)$

If a $=0$ then return b

Else return gcd$($b mod a$,$a$)$

$\{$output is gcd$($a$,$b$)\}$

int commonfactor $=$ gcd$(21,49)$; What are the recursive calls and their return values

Arguments:

Return statement:

$($base case OR recursive call$)$: