**NumbersAsWords

using System;
class NumbersAsWords
{
    static void Main()
    {
        string input;
        int number;
        bool isValid;
        bool isUK = false;

        do
        {
            Console.Write("Enter integer : ");
            input = Console.ReadLine();
            isValid = int.TryParse(input, out number);
            if (!isValid)
                Console.WriteLine("\n  Not an integer, please try again\n");
            else
                Console.WriteLine("\n  {0}\n", NumberToText(number, isUK));
        }
        while (!(isValid && number == 0));
        Console.WriteLine("\nProgram ended");
    }
    public static string NumberToText(int number, bool isUK)
    {
        if (number == 0) return "Zero";
        string and = isUK ? "and " : ""; // deals with UK or US numbering
        if (number == -2147483648) return "Minus Two Billion One Hundred " + and +
        "Forty Seven Million Four Hundred " + and + "Eighty Three Thousand " +
        "Six Hundred " + and + "Forty Eight";
        int[] num = new int[4];
        int first = 0;
        int u, h, t;
        System.Text.StringBuilder sb = new System.Text.StringBuilder();
        if (number < 0)
        {
            sb.Append("Minus ");
            number = -number;
        }
        string[] words0 = { "", "One ", "Two ", "Three ", "Four ", "Five ", "Six ", "Seven ", "Eight ", "Nine " };
        string[] words1 = { "Ten ", "Eleven ", "Twelve ", "Thirteen ", "Fourteen ", "Fifteen ", "Sixteen ", "Seventeen ", "Eighteen ", "Nineteen " };
        string[] words2 = { "Twenty ", "Thirty ", "Forty ", "Fifty ", "Sixty ", "Seventy ", "Eighty ", "Ninety " };
        string[] words3 = { "Thousand ", "Million ", "Billion " };
        num[0] = number % 1000;           // units
        num[1] = number / 1000;
        num[2] = number / 1000000;
        num[1] = num[1] - 1000 * num[2];  // thousands
        num[3] = number / 1000000000;     // billions
        num[2] = num[2] - 1000 * num[3];  // millions
        for (int i = 3; i > 0; i--)
        {
            if (num[i] != 0)
            {
                first = i;
                break;
            }
        }
        for (int i = first; i >= 0; i--)
        {
            if (num[i] == 0) continue;
            u = num[i] % 10;              // ones
            t = num[i] / 10;
            h = num[i] / 100;             // hundreds
            t = t - 10 * h;               // tens
            if (h > 0) sb.Append(words0[h] + "Hundred ");
            if (u > 0 || t > 0)
            {
                if (h > 0 || i < first) sb.Append(and);
                if (t == 0)
                    sb.Append(words0[u]);
                else if (t == 1)
                    sb.Append(words1[u]);
                else
                    sb.Append(words2[t - 2] + words0[u]);
            }
            if (i != 0) sb.Append(words3[i - 1]);
        }
        return sb.ToString().TrimEnd();
    }
}