private string getExistingRegistrationNumberFromUser() { string userInput = string.Empty; Console.Write(@"Please enter registration number (7 characters, 0-9, 'A'-'Z'): >> "); userInput = Console.ReadLine(); if (StringManager.IsOnlyDigitsAndCapLetters(userInput) == true && userInput.Length == 7) { if (m_Garage.IsVehicleExists(userInput) == false) { throw new ArgumentException("Vehicle_Not_Exist"); } } else { throw new Exception("Invalid data input"); } return(userInput); }