NumberAsWords

using System;

/*11* Write a program that converts a number in the range [0…999] to words, corresponding to the English pronunciation. Examples:
0	Zero
9	Nine
19	Nineteen
25	Twenty five
98	Ninety eight
273	Two hundred and seventy three
400	Four hundred
501	Five hundred and one
617	Six hundred and seventeen
999	Nine hundred and ninety nine
*/

class NumberAsWords
{
    static void Main()
    {
        Console.Write("Enter a number [0…999]: ");
        string input = Console.ReadLine();
        int number = int.Parse(input);

        string[] units = { "Zero", "one", "two", "tree", "four", "five", "six", "seven", "eight", "nine", "ten", "eleven",
	                               "twelve", "thirdteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen" };
        string[] tens = { "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety" };

        int remainder = number % 100;
        int numDiv = number / 10;
        string hundreds = units[number / 100];

        if (number >= 0 && number < 100) // [0...99]
        {
            if (number >=0 && number < 20) // 0... 20
            {
                Console.WriteLine("{0}", units[number]);
            }
            else if (number % 10 == 0) //20,30... 90
            {
                Console.WriteLine("{0}", tens[numDiv - 2]);
            }
            else if (number >= 20 && number < 100) // 21 to 99
            {
                Console.WriteLine("{0} {1}", tens[numDiv - 2], units[number % 10]);
            }
        }
        else
        {
            if (remainder == 0)    // 100,200,300...900
            {
                Console.WriteLine("{0} hundred", hundreds);
            }
            else if (remainder > 0 && remainder < 20)   //from x00 to x20
            {
                Console.WriteLine("{0} hundred and {1}", hundreds, units[remainder]);
            }
            else if (remainder % 10 == 0) // x10, x20... x90
            {
                Console.WriteLine("{0} hundred and {1}", hundreds, tens[remainder / 10 - 2]);
            }
            else if (remainder > 20 && remainder < 100) //from x20 to x99
            {
                Console.WriteLine("{0} hundred and {1} {2}", hundreds, tens[remainder / 10 - 2], units[remainder % 10]);
            }
        }
    }
}