int add(const char* number1, const char* number2, char** result)
{
    if (number1 == NULL || number2 == NULL || result == NULL) return 1;
    if (validate(number1) == 2 || validate(number2) == 2) return 2;
    int dl1 = strlen(number1), dl2 = strlen(number2),dlmax;
    if (dl1 >= dl2) dlmax = dl1;
    else dlmax = dl2;
    dlmax += 3;//ewentualne znaki
    if (*number1 == '-' && *number2 != '-')
        return subtract(number2, number1 + 1, result);
    if (*number1 != '-' && *number2 == '-')
        return subtract(number1, number2 + 1, result);
    *result = (char*)malloc(dlmax * sizeof(char));
    if (*result == NULL)
        return 3;

    if (*number1 == '-' && *number2 == '-')
    {
        int carry = 0, digit1, digit2, i;
        for (i = 0; i < dlmax - 1; i++)
        {
            /*wylaczenie liczby*/
            if (dl1 - 1 - i <= 0) digit1 = 0;
            else digit1 = *(number1 + dl1 - 1 - i) - '0';
            if (dl2 - 1 - i <= 0) digit2 = 0;
            else digit2 = *(number2 + dl2 - 1 - i) - '0';
            if (dl1 - 1 - i <= 0 && dl2 - 1 - i <= 0 && carry == 0)
                break;
            dodanie(digit1, digit2, &carry, result,i);
        }
        *(*result + i) = '-';
        *(*result + i + 1) = '\0';
        rev(*result);
        return 0;
    }
    if (*number1 != '-' && *number2 != '-')
    {
        int carry = 0, digit1, digit2, i;
        for (i = 0; i < dlmax - 1; i++)
        {
            /*wylaczenie liczby*/
            if (dl1 - 1 - i < 0) digit1 = 0;
            else digit1 = *(number1 + dl1 - 1 - i) - '0';
            if (dl2 - 1 - i < 0) digit2 = 0;
            else digit2 = *(number2 + dl2 - 1 - i) - '0';
            if (dl1 - 1 - i < 0 && dl2 - 1 - i < 0 && carry == 0)break;
            dodanie(digit1, digit2, &carry, result, i);
        }
        *(*result + i) = '\0';
        rev(*result);
        return 0;
    }
    return 0;
}
void dodanie(int digit1, int digit2, int *carry, char** result,int i)
{
    if (digit1 + digit2 + *carry >= 10)
    {
        *(*result + i) = (digit2 + digit1 + *carry) % 10 + '0';
        *carry = 1;
    }
    else
    {
        *(*result + i) = (digit2 + digit1 + *carry) % 10 + '0';
        *carry = 0;
    }
}