NumbersToText - Chapter 3.0

//Task 016, Chapter 3.0
using System;

public class NumbersToText
{
    static void Main()
    {
        var number = int.Parse(Console.ReadLine());
        string posDec = "";
        string posOne = "";
        string posTeen = "";
        string numWord = "";

        if (number >= 0 && number < 100)
        {
            // Number BETWEEN 0 and 99 [0..99]
            var digitDEC = number / 10;
            var digitONE = number % 10;

            switch (digitONE)
            {
                case 0: posOne = "zero"; break;
                case 1: posOne = "one"; break;
                case 2: posOne = "two"; break;
                case 3: posOne = "three"; break;
                case 4: posOne = "four"; break;
                case 5: posOne = "five"; break;
                case 6: posOne = "six"; break;
                case 7: posOne = "seven"; break;
                case 8: posOne = "eight"; break;
                case 9: posOne = "nine"; break;
                default: break;
            };

            switch (digitDEC)
            {
                case 1:
                    {
                        switch (number)
                        {
                            case 10: posTeen = "ten"; break;
                            case 11: posTeen = "eleven"; break;
                            case 12: posTeen = "twelve"; break;
                            case 13: posTeen = "thirteen"; break;
                            case 14: posTeen = "fourteen"; break;
                            case 15: posTeen = "fifteen"; break;
                            case 16: posTeen = "sixteen"; break;
                            case 17: posTeen = "seventeen"; break;
                            case 18: posTeen = "eighteen"; break;
                            case 19: posTeen = "nineteen"; break;
                            default: break;
                        }
                    }; break;
                case 2: posDec = "twenty"; break;
                case 3: posDec = "thirty"; break;
                case 4: posDec = "fourty"; break;
                case 5: posDec = "fifty"; break;
                case 6: posDec = "sixty"; break;
                case 7: posDec = "seventy"; break;
                case 8: posDec = "eighty"; break;
                case 9: posDec = "ninety"; break;
                default: break;
            }


            if (number == 0)
            {
                numWord = posOne;
            }
            else
            {
                if (digitDEC == 1)
                {
                    numWord = posTeen;
                }
                else
                {
                    if (number > 19)
                    {
                        switch (digitONE)
                        {
                            case 0: numWord = posDec; break;
                            default: numWord = posDec + " " + posOne; break;
                        }
                    }
                    else
                    {
                        if (digitDEC == 0)
                        {
                            numWord = posOne;
                        }
                    }


                }
            }

            Console.WriteLine(numWord);
        } // If [0..99]
        else
        {
            if (number == 100)
            {
                Console.WriteLine("one hundred");
            }
            else
            {
                Console.WriteLine("invalid number");
            }
        }
    }
}