using System;
using System.Linq;
using System.Text;


namespace ThreeDigitNumberToString
{
    class Program
    {
        private enum firstTwenty
        {
            zero, one, two, three, four, five, six, seven,
            eight, nine, ten, eleven, twelve, thirteen, fourteen, fifteen, sixteen, seventeen,
            eighteen, nineteen,
        };

        private enum tens {twenty = 2, thirty, fourty, fifty, sixty, seventy, eighty, ninety };

        static void Main(string[] args)
        {
            int number = EnterThreeDigitNumber();
            ConvertNumberToText(number);
        }

        static int EnterThreeDigitNumber ()
        {
            int number;

            do
            {
                Console.Write("Enter valid number in the interval [0-999]: ");

            } while (!int.TryParse(Console.ReadLine(), out number) || number < 0 || number > 999);

            return number;
        }

        static void ConvertNumberToText(int number)
        {
            int hundredsRemainder = number / 100;
            int tensRemainder = number % 100 / 10;
            int tensValue = number % 100;
            int ones = number % 100 % 10;

            string onesText = (ones != 0 ? ((firstTwenty)ones).ToString() : "");
            string tensText = (tensRemainder != 0 ? (" and " + (firstTwenty)tensValue).ToString() : "");

            //Numbers bigger than 100
            if (hundredsRemainder != 0)
            {
                if (tensRemainder < 2)
                {
                    // (firstTwenty)hundredsRemainder allows access to member of enum by index.
                    Console.WriteLine((firstTwenty)hundredsRemainder + " hundred " + tensText);
                }

                else
                {
                    Console.WriteLine((firstTwenty)hundredsRemainder + " hundred " + " and "
                        + (tens)tensRemainder + " " + onesText);
                }
            }

            //Numbers smaller than 100
            else
            {
                if (tensRemainder < 2)
                {
                    Console.WriteLine((firstTwenty)tensValue);
                }
                else
                {
                    Console.WriteLine((tens)tensRemainder + " " + onesText);
                }
            }
        }
    }
}