C# Convert Integers into Written Numbers

Question

Is there an efficient method of converting an integer into the written numbers for example:

String Written = IntegerToWritten(21);

would return "Twenty One"

Is there any way of doing this that doesn't involve a massive lookup table?

Answer 1

why massive lookup table?

string GetWrittenInteger(int n)
{
  string[] a = new string[] {"One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine" }
  string[] b = new string[] { "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen" }
  string[] c = new string[] {"Twenty", "Thirty", "Forty", "Sixty", "Seventy", "Eighty", "Ninety"};
  string[] d = new string[] {"Hundred", "Thousand", "Million"}

  string s = n.ToString();
  for (int i = 0; i < s.Length; i++)
  {
    // logic (too lazy but you get the idea)
  }
}

Answer 2

Here are the correct links to the posts by Justin Rogers: initial post, code only.

There is also an article on CodeProject that addresses this issue.

Answer 3

I use this code.It is VB code but you can easily translate it to C#. It works

Function NumberToText(ByVal n As Integer) As String

   Select Case n
Case 0
  Return ""

Case 1 To 19
  Dim arr() As String = {"One","Two","Three","Four","Five","Six","Seven", _
    "Eight","Nine","Ten","Eleven","Twelve","Thirteen","Fourteen", _
      "Fifteen","Sixteen","Seventeen","Eighteen","Nineteen"}
  Return arr(n-1) & " "

Case 20 to 99
  Dim arr() as String = {"Twenty","Thirty","Forty","Fifty","Sixty","Seventy","Eighty","Ninety"}
  Return arr(n\10 -2) & " " & NumberToText(n Mod 10)

Case 100 to 199
  Return "One Hundred " & NumberToText(n Mod 100)

Case 200 to 999
  Return NumberToText(n\100) & "Hundreds " & NumberToText(n mod 100)

Case 1000 to 1999
  Return "One Thousand " & NumberToText(n Mod 1000)

Case 2000 to 999999
  Return NumberToText(n\1000) & "Thousands " & NumberToText(n Mod 1000)

Case 1000000 to 1999999
  Return "One Million " & NumberToText(n Mod 1000000)

Case 1000000 to 999999999
  Return NumberToText(n\1000000) & "Millions " & NumberToText(n Mod 1000000)

Case 1000000000 to 1999999999
  Return "One Billion " & NumberTotext(n Mod 1000000000)

Case Else
  Return NumberToText(n\1000000000) & "Billion " _
    & NumberToText(n mod 1000000000)
End Select
End Function

Answer 4

This should work reasonably well:

public static class HumanFriendlyInteger
{
    static string[] ones = new string[] { "", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine" };
    static string[] teens = new string[] { "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen" };
    static string[] tens = new string[] { "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety" };
    static string[] thousandsGroups = { "", " Thousand", " Million", " Billion" };

    private static string FriendlyInteger(int n, string leftDigits, int thousands)
    {
        if (n == 0)
        {
            return leftDigits;
        }
        string friendlyInt = leftDigits;
        if (friendlyInt.Length > 0)
        {
            friendlyInt += " ";
        }

        if (n < 10)
        {
            friendlyInt += ones[n];
        }
        else if (n < 20)
        {
            friendlyInt += teens[n - 10];
        }
        else if (n < 100)
        {
            friendlyInt += FriendlyInteger(n % 10, tens[n / 10 - 2], 0);
        }
        else if (n < 1000)
        {
            friendlyInt += FriendlyInteger(n % 100, (ones[n / 100] + " Hundred"), 0);
        }
        else
        {
            friendlyInt += FriendlyInteger(n % 1000, FriendlyInteger(n / 1000, "", thousands+1), 0);
        }

        return friendlyInt + thousandsGroups[thousands];
    }

    public static string IntegerToWritten(int n)
    {
        if (n == 0)
        {
            return "Zero";
        }
        else if (n < 0)
        {
            return "Negative " + IntegerToWritten(-n);
        }

        return FriendlyInteger(n, "", 0);
    }

}

(Edited to make it considerably more concise.)