John Regard

first, take out the while loop from the recursive function and put it on the main function instead.
then, your prorgam function should look something like
// iterative version int rev_num = 0; while(n){ rev_num = rev_num * 10 + n % 10; n /= 10; } // recursive version int reverse(int n, int rev_num=0){ if (n == 0) return rev_num; return reverse(n / 10, rev_num * 10 + n % 10); }