Introduction

A question which is often asked on programming forums is - how do I convert a number to words?

Although many solutions have been posted over the years, we appear to be lacking a basic article on the subject here on C# Corner.

In this article, I'd therefore like to present a simple program which I've written to deal with this question for integers in the range of an Int32 (about plus or minus 2 billion) which I believe is the most useful case.

The program supports both the US and UK numbering systems. 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)

Source Code

using System;
class Program
{
    static void Main()
    {
        string input;
        int number;
        bool isValid;
        bool isUK = false;
        Console.WriteLine("\nEnter '0' to quit the program at any time\n");
        while (true)
        {
            Console.Write("\nUse UK numbering y/n : ");
            input = Console.ReadLine();
            if (!(input.ToLower() == "y" || input.ToLower() == "n"))
                Console.WriteLine("\n  Must be 'y' or 'n', please try again\n");
            else
            {
                if (input.ToLower() == "y") isUK = true;
                Console.WriteLine("\n");
                break;
            }
        }
        do
        {
            Console.Write("Enter integer : ");
            input = Console.ReadLine();
            isValid = int.TryParse(input, out number);
            if (!isValid)
                Console.WriteLine("\n  Not an integer, please try again\n");
            else
                Console.WriteLine("\n  {0}\n", NumberToText(number, isUK));
        }
        while (!(isValid && number == 0));
        Console.WriteLine("\nProgram ended");
    }
    public static string NumberToText(int number, bool isUK)
    {
        if (number == 0) return "Zero";
        string and = isUK ? "and " : ""; // deals with UK or US numbering
        if (number == -2147483648) return "Minus Two Billion One Hundred " + and +
        "Forty Seven Million Four Hundred " + and + "Eighty Three Thousand " +
        "Six Hundred " + and + "Forty Eight";
        int[] num = new int[4];
        int first = 0;
        int 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 " };
        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;     // billions
        num[2] = num[2] - 1000 * num[3];  // millions
        for (int i = 3; 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();
    }
}

Conclusion

It would not be difficult to extend this program to deal with larger integers, with decimal numbers or with specific currencies and I leave this as an exercise to those who need this functionality.