NumbersAsWordsWithMethods

using System;
using System.Globalization;

class NumbersAsWords
{
    static void Main()
    {
        for (int i = 0; i < 1000; i++)
        {
            Console.WriteLine("{0,3}: {1}", i, GetNumberAsWords(i));
        }
    }

    static string GetNumberAsWords(int a)
    {
        string sentence = "";
        string word = "";
        if (a >= 100 && a < 1000)
        {
            word = GetDigitAsWord(a / 100);
            if (sentence == "")
            {
                sentence += FirstLetterToUpper(word);
            }
            else
            {
                sentence += word;
            }
            sentence += " hundred";
        }

        if ((a >= 10 && a < 20) || (a % 100 >= 10 && a % 100 < 20))
        {
            if (a >= 100 && a < 1000 && a % 100 != 0)
            {
                sentence += " and ";
            }

            word = Get10To19AsWord(a % 100);
            if (sentence == "")
            {
                sentence += FirstLetterToUpper(word);
            }
            else
            {
                sentence += word;
            }
            return sentence;
        }

        if ((a >= 20 && a < 100) || (a % 100 >= 20 && a % 100 < 100))
        {
            if (a >= 100 && a < 1000 && a % 100 != 0)
            {
                sentence += " and ";
            }
            word = Get20To99AsWord(a % 100);
            if (sentence == "")
            {
                sentence += FirstLetterToUpper(word);
            }
            else
            {
                sentence += word;
            }
        }

        if ((a >= 0 && a <= 9) || (a % 10 >= 0 && a % 10 <= 9))
        {
            if ((a >= 20 && a < 100) || (a % 100 >= 20 && a % 100 < 100))
            {
                sentence += " ";
            }
            else if (a >= 100 && a < 1000 && a % 10 != 0)
            {
                sentence += " and ";
            }

            word = GetDigitAsWord(a % 10);
            if (sentence == "")
            {
                sentence += FirstLetterToUpper(word);
            }
            else
            {
                sentence += word;
            }
        }

        if (a == 0)
        {
            sentence += "Zero";
        }

        return sentence;
    }

    static string GetDigitAsWord(int n)
    {
        string word = "";
        switch (n)
        {
//            case 0:
//                word = "zero";
//                break;
            case 1:
                word = "one";
                break;
            case 2:
                word = "two";
                break;
            case 3:
                word = "three";
                break;
            case 4:
                word = "four";
                break;
            case 5:
                word = "five";
                break;
            case 6:
                word = "six";
                break;
            case 7:
                word = "seven";
                break;
            case 8:
                word = "eight";
                break;
            case 9:
                word = "nine";
                break;
            default:
                word = "";
                break;
        }
        return word;
    }

    static string Get10To19AsWord(int n)
    {
        string word = "";
        switch (n)
        {
            case 10:
                word = "ten";
                break;
            case 11:
                word = "eleven";
                break;
            case 12:
                word = "twelve";
                break;
            case 13:
                word = "thirteen";
                break;
            case 14:
                word = GetDigitAsWord(n % 10) + "teen";
                break;
            case 15:
                word = "fifteen";
                break;
            case 16:
            case 17:
            case 18:
            case 19:
                word = GetDigitAsWord(n % 10) + "teen";
                break;
            default:
                word = "";
                break;
        }
        return word;
    }

    static string Get20To99AsWord(int n)
    {
        string word = "";
        switch (n / 10)
        {
            case 20/10:
                word = "twenty";
                break;
            case 30/10:
                word = "thirty";
                break;
            case 40/10:
                word = GetDigitAsWord(n / 10) + "ty";
                break;
            case 50/10:
                word = "fifty";
                break;
            case 60/10:
            case 70/10:
                word = GetDigitAsWord(n / 10) + "ty";
                break;
            case 80/10:
                word = GetDigitAsWord(n / 10) + "y";
                break;
            case 90/10:
                word = GetDigitAsWord(n / 10) + "ty";
                break;
            default:
                word = "";
                break;
        }
        return word;
    }

    static public string FirstLetterToUpper(string str)
    {
        if (str == null)
            return null;

        if (str.Length > 1)
            return char.ToUpper(str[0]) + str.Substring(1);

        return str.ToUpper();
    }

    // Old answer: This makes every first letter to upper case
    /* http://stackoverflow.com/questions/4135317/make-first-letter-of-a-string-upper-case-for-maximum-performance#4135491 */
    public string ToTitleCase(string str)
    {
        return CultureInfo.CurrentCulture.TextInfo.ToTitleCase(str.ToLower());
    }
}