enum class Result
{
   Success,
   Error
};

[[nodiscard]]Result CalculateFactorial(const int value, int &result)
{
   if (value < 0)
   {
       result = -1;
       return Result::Error;
   }

   result = 1;
   for(int i = 2; i <= value; ++i)
   {
       result *= i;
   }
   return Result::Success;
}

int main()
{
   int factorial;
   auto x = CalculateFactorial(5, factorial);
   (void)x;
   std::cout << "factorial is " << factorial << std::endl;
   return 0;
}