std::string _add(std::string a, std::string b)
{
    std::string temp = ""; //return value

    std::string* bigger_string;
    if (a.length() >= b.length()) bigger_string = &a;
    else bigger_string = &b;

    std::string * smaller_string;
    if (b.length() <= a.length()) smaller_string = &b;
    else smaller_string = &a;

    std::reverse(bigger_string->begin(), bigger_string->end());
    std::reverse(smaller_string->begin(), smaller_string->end());

    int buffor = 0;
    for (int i = 0; i < smaller_string->length(); i++)
    {
        int _a = (int)(*bigger_string)[i] - 48;
        int _b = (int)(*smaller_string)[i] - 48;
        int _temp = _a + _b + buffor;

        temp += std::to_string(_temp % 10);
        buffor = _temp / 10;
    }
    for (int i = smaller_string->length(); i < bigger_string->length(); i++)
    {
        int _a = (int)(*bigger_string)[i] - 48;
        int _temp = _a + buffor;

        temp += std::to_string(_temp % 10);
        buffor = _temp / 10;
    }
    if (buffor > 0)
    {
        temp += std::to_string(buffor);
    }

    std::reverse(temp.begin(), temp.end());

    return temp;
}