How can I convert an integer into its verbal representation?

Question

Is there a library or a class/function that I can use to convert an integer to it\'s verbal representation?

Example input:

4,567,788`

Answer 1

I actually needed this for an app I'm working on, but wasn't happy with any of the solutions here. FYI, this solution takes advantage of C# 7.0's support for local functions. I also used the new digit separator to make the larger numbers more readable.

public static class NumberExtensions
{
    private const string negativeWord = "negative";
    private static readonly Dictionary _wordMap = new Dictionary
    {
        [1_000_000_000_000_000_000] = "quintillion",
        [1_000_000_000_000_000] = "quadrillion",
        [1_000_000_000_000] = "trillion",
        [1_000_000_000] = "billion",
        [1_000_000] = "million",
        [1_000] = "thousand",
        [100] = "hundred",
        [90] = "ninety",
        [80] = "eighty",
        [70] = "seventy",
        [60] = "sixty",
        [50] = "fifty",
        [40] = "forty",
        [30] = "thirty",
        [20] = "twenty",
        [19] = "nineteen",
        [18] = "eighteen",
        [17] = "seventeen",
        [16] = "sixteen",
        [15] = "fifteen",
        [14] = "fourteen",
        [13] = "thirteen",
        [12] = "twelve",
        [11] = "eleven",
        [10] = "ten",
        [9] = "nine",
        [8] = "eight",
        [7] = "seven",
        [6] = "six",
        [5] = "five",
        [4] = "four",
        [3] = "three",
        [2] = "two",
        [1] = "one",
        [0] = "zero"
    };

    public static string ToWords(this short num)
    {
        var words = ToWords((ulong)Math.Abs(num));
        return num < 0 ? $"{negativeWord} {words}" : words;
    }

    public static string ToWords(this ushort num)
    {
        return ToWords((ulong)num);
    }

    public static string ToWords(this int num)
    {
        var words = ToWords((ulong)Math.Abs(num));
        return num < 0 ? $"{negativeWord} {words}" : words;
    }

    public static string ToWords(this uint num)
    {
        return ToWords((ulong)num);
    }

    public static string ToWords(this long num)
    {
        var words = ToWords((ulong)Math.Abs(num));
        return num < 0 ? $"{negativeWord} {words}" : words;
    }

    public static string ToWords(this ulong num)
    {
        var sb = new StringBuilder();
        var delimiter = String.Empty;

        void AppendWords(ulong dividend)
        {
            void AppendDelimitedWord(ulong key)
            {
                sb.Append(delimiter);
                sb.Append(_wordMap[key]);
                delimiter = 20 <= key && key < 100 ? "-" : " ";
            }

            if (_wordMap.ContainsKey(dividend))
            {
                AppendDelimitedWord(dividend);
            }
            else
            {
                var divisor = _wordMap.First(m => m.Key <= dividend).Key;
                var quotient = dividend / divisor;
                var remainder = dividend % divisor;

                if (quotient > 0 && divisor >= 100)
                {
                    AppendWords(quotient);
                }

                AppendDelimitedWord(divisor);

                if (remainder > 0)
                {   
                    AppendWords(remainder);
                }
            }
        }

        AppendWords(num);
        return sb.ToString();
    }    
}

The meat is in the last ToWords overload.