Number_as_Words

using System;

namespace Problem_11__Number_as_Words
{
    class NumberAsWords
    {
        public static void Main ()
        {
            Console.WriteLine ("Please enter an integer from 0 to 999 inclusive:");
            ushort number = 0;

            try
            {
                number = ushort.Parse (Console.ReadLine());
            }
            catch (Exception e)
            {
                if (e is FormatException)
                {
                    Exception fe = new FormatException ("Error! Input was not in the correct format!");
                    Console.WriteLine (fe.Message);
                }
                else if (e is OverflowException)
                {
                    Exception oe = new OverflowException("Error! Input should be a positive 16-bit integer!");
                    Console.WriteLine (oe.Message);
                }
                else
                {
                    Console.WriteLine ("Error occured!!!");
                }
                return;
            }

            if (number < 0 || number > 999)
            {
                Console.WriteLine ("Invalid Input! Number should be in the range 0 - 999!");
                return;
            }

            // Declare the output...
            string output = "";

            // Set some important values (I'll use arrays)...
            /*-------------------------------------------------*/
            // First array will store the names of the first 20 numbers (from 0 to 19).
            string[] singles = {
                "Zero", "One", "Two",
                "Three", "Four", "Five",
                "Six", "Seven", "Eight",
                "Nine", "Ten", "Eleven",
                "Twelve", "Thirteen", "Fourteen",
                "Fifteen", "Sixteen", "Seventeen",
                "Eighteen", "Nineteen"
            };
            // Second array will store the names of the decimals (20, 30, ..., 90).
            string[] decimals = {
                "Twenty", "Thirty", "Fourty",
                "Fifty", "Sixty", "Seventy",
                "Eighty", "Ninety"
            };

            // Here comes the Magic... :-)

            // Some bools to make it easier...
            bool isBetween0and19 = (number >= 0) && (number <= 19);
            bool isBetween19and99 = (number > 19) && (number <= 99);
            bool isBeween100and999 = (number >= 100) && (number <= 999);

            // Now, we have 3 cases...
            // Range(0-19), Range(19-99) and Range(100-999)

            // 0-19
            if (isBetween0and19)
            {
                output = TransformLowRangeNumber (number, singles);
            }
            // 19-99
            else if (isBetween19and99)
            {
                output = TransformMiddleRangeNumber (number, singles, decimals);
            }
            // 100-999
            else if (isBeween100and999)
            {
                output = TransformHighRangeNumber (number, singles, decimals);
            }

            Console.WriteLine (output);
        }

        public static string TransformLowRangeNumber (ushort number, string[] singles)
        {
            return singles [number];
        }

        public static string TransformMiddleRangeNumber (ushort number, string[] singles, string[] decimals)
        {
            ushort ones = (ushort)(number % 10);
            ushort decs = (ushort)((number / 10) % 10);

            if (ones == 0)
            {
                return decimals [decs - 2];
            }

            return decimals [decs - 2] + " " + singles[ones].ToLower();
        }

        static string TransformHighRangeNumber (ushort number, string[] singles, string[] decimals)
        {
            ushort ones = (ushort)(number % 10);
            ushort decs = (ushort)((number / 10) % 10);
            ushort hunds = (ushort)((number / 100) % 10);

            if (number == 100)
            {
                return singles[hunds] + " hundred";
            }

            if (decs < 2)
            {
                ones += (ushort)(10 * decs);
                return singles [hunds] + " hundred and " + singles [ones].ToLower();
            }
            else
            {
                if (ones == 0)
                {
                    return singles [hunds] + " hundred and " + decimals [decs - 2].ToLower();
                }
                return singles [hunds] + " hundred and " + decimals [decs - 2].ToLower() + " " + singles [ones].ToLower();
            }
        }
    }
}