How to convert Numerical Value into Words Format

Here's a method I wrote a while back which should do what you want. I've placed it inside a console app for testing purposes. Notice that it optionally supports UK style number/word  translation i.e. One Hundred and Twenty Four as opposed to One Hundred Twenty Four. However, it doesn't support numbers with decimal points.

using System;

class Program
{
  static void Main()
  {

    string input;
    int number;
    bool isValid;
    bool isUK = false;

    Console.WriteLine("\nEnter '0' to quit the program at any time\n");
    while(true)
    {
      Console.Write("\nUse UK numbering y/n : ");
      input = Console.ReadLine();
      if (!(input.ToLower() == "y" || input.ToLower() == "n"))
        Console.WriteLine("\n  Must be 'y' or 'n', please try again\n");
      else
      {
        if(input.ToLower() == "y") isUK = true;
        Console.WriteLine("\n");
        break;
      }
    }            
               
    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();
  }

} // end class