Convert integers to written numbers

Solution 1:

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);
            if (n % 1000 == 0)
            {
                return friendlyInt;
            }
        }

        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 fix a bug w/ million, billion, etc.)

Solution 2:

I use this handy library called Humanizer.

https://github.com/Humanizr/Humanizer

It supports several cultures and converts not only numbers to words but also date and it's very simple to use.

Here's how I use it:

int someNumber = 543;
var culture = System.Globalization.CultureInfo("en-US");
var result = someNumber.ToWords(culture); // 543 -> five hundred forty-three

And voilá!

Solution 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

Here is the code in c#

public static string AmountInWords(double amount)
{
        var n = (int)amount;

        if (n == 0)
            return "";
        else if (n > 0 && n <= 19)
        {
            var arr = new string[] { "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen" };
            return arr[n - 1] + " ";
        }
        else if (n >= 20 && n <= 99)
        {
            var arr = new string[] { "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety" };
            return arr[n / 10 - 2] + " " + AmountInWords(n % 10);
        }
        else if (n >= 100 && n <= 199)
        {
            return "One Hundred " + AmountInWords(n % 100);
        }
        else if (n >= 200 && n <= 999)
        {
            return AmountInWords(n / 100) + "Hundred " + AmountInWords(n % 100);
        }
        else if (n >= 1000 && n <= 1999)
        {
            return "One Thousand " + AmountInWords(n % 1000);
        }
        else if (n >= 2000 && n <= 999999)
        {
            return AmountInWords(n / 1000) + "Thousand " + AmountInWords(n % 1000);
        }
        else if (n >= 1000000 && n <= 1999999)
        {
            return "One Million " + AmountInWords(n % 1000000);
        }
        else if (n >= 1000000 && n <= 999999999)
        {
            return AmountInWords(n / 1000000) + "Million " + AmountInWords(n % 1000000);
        }
        else if (n >= 1000000000 && n <= 1999999999)
        {
            return "One Billion " + AmountInWords(n % 1000000000);
        }
        else
        {
            return AmountInWords(n / 1000000000) + "Billion " + AmountInWords(n % 1000000000);
        }
    }