C++不用任何算术运算符实现整数加法

这本是careerup的一道题，看到了以后自己做了一下，主要的难点就是加法里面的进位。直接上代码：

int  add(int a, int b)
{
    const int bitsize = sizeof(int) * 8;
    int digit[bitsize] = {0};
    int first = a, second = b;
    int carry =0;
    int result = 0;
    for (int i = 0; i < bitsize; i++)
    {
        
        digit[i] = (first & 1) ^ (second & 1) ^ carry;

        if (((first & 1) == 1 && (second & 1) == 1) || ((first & 1) == 1 && carry == 1) || (carry == 1 && (second & 1) == 1))
            carry = 1;
        else
            carry = 0;

        first = first >> 1;
        second = second >> 1;

        result = result | (digit[i] << i);
    }
    return result;
    
}

后来网上发现了一个更加简便的方法：

int add_no_arithm(int a, int b)
{
    if (b == 0) return a;
    int sum = a ^ b; // add without carrying
    int carry = (a & b) << 1; // carry, but don’t add
    return add_no_arithm(sum, carry); // recurse
}

真是巧妙啊，carry就是需要进位的地方。