add strings.cpp

class Solution
{
public:
     string addStrings(string num1, string num2)
     {

          string result;
          int i = num1.size() - 1, j = num2.size() - 1;
          int carry = 0;
          while (i >= 0 || j >= 0)
          {
               int sum = carry;
               if (i >= 0)
               {
                    sum += num1[i--] - '0';
               }
               if (j >= 0)
               {
                    sum += num2[j--] - '0';
               }
               carry = sum > 9 ? 1 : 0;
               result += to_string(sum % 10);
          }
          if (carry)
               result += to_string(carry);
          reverse(result.begin(), result.end());
          return result;
     }
};

// l;eetcode - 415