What is the best way to add two numbers without using the + operator?

Question

A friend and I are going back and forth with brain-teasers and I have no idea how to solve this one. My assumption is that it\'s possible with some bitwise operators, but n

Answer 1

CMS's add() function is beautiful. It should not be sullied by unary negation (a non-bitwise operation, tantamount to using addition: -y==(~y)+1). So here's a subtraction function using the same bitwise-only design:

int sub(int x, int y) {
    unsigned a, b;
    do {
        a = ~x & y;
        b =  x ^ y;
        x = b;
        y = a << 1;
    } while (a);
    return b;
}