#include <stdio.h>

int add (int a, int b)
{
    int c = b & a;

    while (a)
    {
        c = b & a;
        b = b ^ a;
        c <<= 1;
        a = c;
    }

    return b;
}

int main (void)
{
    printf ("1 + 1 is %i.\n", add(1, 1));
    printf ("2 + 2 is %i.\n", add(2, 2));
    printf ("4 + 7 is %i.\n", add(4, 7));

    return 0;
}