Add without +

Write a program to add two numbers a and b.
1. Without Using + operator
2. Without using any loops

Sum = A XOR B
Carry = A AND B

#include <iostream>

int add(int p, int q)
{
  if(q == 0)
    return p;
  int k, r;
  k = p ^ q;
  r = p & q;
  return add(k, r<<1); // carry left shift 1 bit
}

int main() {
  printf("%d\n", add(4,7));
  printf("%d\n", add(401,7));
  printf("%d\n", add(14,7));
  printf("%d\n", add(4,47));
  printf("%d\n", add(4,-97));
  printf("%d\n", add(-4,-97));
}

output:

11
408
21
51
-93
-101