#include <iostream>

int sum(int a, int b) {
    int a_bit, b_bit, carry = 0, result=0;
    for(int i=0; i<sizeof(int) * 8; i++) {
        a_bit = (a >> i) & 1;
        b_bit = (b >> i) & 1;
        switch(a_bit + b_bit + carry) {
        case 0:
            result &= ~(1 << i); // clear
            carry = 0;
        break;
        case 1:
            result |= 1 << i; // set
            carry = 0;
        break;
        case 2:
            result &= ~(1 << i); // clear
            carry = 1;
        break;
        case 3:
            result |= 1 << i; // set
            carry = 1;
        }
    }

    return result;
}

int main() {
    std::cout << sum(255, 3) << std::endl;
}