Convert integers to 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 look-up table?

Answer 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.)

Answer 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!