Convert numbers to words

If you're only interested in converting integers to words, then try this method:

    public static string NumberToText(long number, bool isUK)

    {

        if (number == 0) return "Zero";

        string and = isUK ? "and " : ""; // deals with UK or US numbering

        if (number == - 9223372036854775808) return "Minus Nine Quintillion Two Hundred " + and + "Twenty Three Quadrillion Three Hundred " + and + "Seventy Two Trillion Thirty Six Billion Eight Hundred " + and + "Fifty Four Million Seven Hundred " + and + "Seventy Five Thousand Eight Hundred " + and + "Eight";

        long[] num = new long[7];

        int first = 0;

        long 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 ", "Trillion ", "Quadrillion ", "Quintillion "};

        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;     

        num[2] = num[2] - 1000 * num[3];       // millions

        num[4] = number / 1000000000000;  

        num[3] = num[3] - 1000 * num[4];       // billions

        num[5] = number / 1000000000000000;    

        num[4] = num[4] - 1000 * num[5];       // trillions

        num[6] = number / 1000000000000000000; // quintillions

        num[5] = num[5] - 1000 * num[6];       // quadrillions

      

        for (int i = 6; 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();

    }

As you want to convert numbers up to 10 billion which is greater than the range of an int, you need to pass a 'long' to this method.

The 'isUK' parameter, if true, will insert the word 'and' in appropriate places in the number, as is the custom in the UK. If false, numbers will be presented in US form.

For example the number 620 would be expressed as follows:

    Six Hundred Twenty   (in the US system)

    Six Hundred and Twenty  (in the UK system)