static void Main(string[] args) { try { do { WriteLine("Enter and number (press ESC to finish):"); string userInput = ReadLine(); if (Regex.IsMatch(userInput, @"^-?[\d]+$")) // takes positive and negative integers { long number = System.Int64.Parse(userInput); WriteLine($"The number in words is: {NumberToWords.ToWords(number)}"); } else { WriteLine("Invalid number entered."); } }while (ReadKey().Key != ConsoleKey.Escape); } catch (System.Exception ex) { WriteLine($"{ex.GetBaseException().ToString()} has message {ex.Message}"); } }