public string AddRomanNumbers(string firstNumber, string secondNumber) { if (!_inputValidator.CheckIfRomanCharacter(firstNumber)) { return(firstNumber + NotRomanError); } if (!_inputValidator.CheckIfRomanCharacter(secondNumber)) { return(secondNumber + NotRomanError); } var firstIntFromRoman = _romanToNumbers.ConvertFromRoman(firstNumber.ToUpper()); var secondIntFromRoman = _romanToNumbers.ConvertFromRoman(secondNumber.ToUpper()); var sum = _calculator.AddNumbers(firstIntFromRoman, secondIntFromRoman); if (!_inputValidator.RangeValidator(sum)) { return(SumError); } var romanWord = new StringBuilder(); romanWord = _romanToNumbers.ConvertToRoman(sum, romanWord); return(romanWord.ToString()); }