class Solution {
public:
    int add(int num1, int num2){
        //用^来表示无进位加法，用&表示进位
        while(num2){
            int sum = num1 ^ num2;
            int carry = (num1 & num2) << 1; //注意运算符优先级，不加括号会错
            num1 = sum;
            num2 = carry;
        }
        return num1;
    }
};