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) * ;
     int digit[bitsize] = {};
     int first = a, second = b;
     int carry =;
     int result = ;
     for (int i = ; i < bitsize; i++)
     {

         digit[i] = (first & ) ^ (second & ) ^ carry;

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

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

         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 == ) return a;
     int sum = a ^ b; // add without carrying
     int carry = (a & b) << ; // 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。