class RomanNumber
    {
        /// <summary>
        /// The possible characters used to represent a single digit in a Roman number.
        /// Example: For tens digit, Ten = C (100), Five = L (50), One = X (10)
        /// </summary>
        class RomanDigit
        {
            public char Ten { get; set; }
            public char Five { get; set; }
            public char One { get; set; }
        }

        #region Constants
        static List<RomanDigit> RomanDigits = new List<RomanDigit>()
        {
            new RomanDigit() {Ten = 'X', Five = 'V', One = 'I'},    // Ones place
            new RomanDigit() {Ten = 'C', Five = 'L', One = 'X'},    // Tens place
            new RomanDigit() {Ten = 'M', Five = 'D', One = 'C'},    // Hundreds place
            new RomanDigit() {One = 'M'},                           // Thousands place
        };
        static int MAX = 3999;
        static int MIN = 0;
        #endregion

        /// <summary>
        /// Converts an Arabic number to a Roman number by converting one digit at a time.
        /// </summary>
        /// <param name="arabic"></param>
        /// <returns></returns>
        public static string ToRoman(int arabic)
        {
            if (arabic > MAX || arabic < MIN) throw new ArgumentOutOfRangeException("Arabic number must between 0 and 3999.");
            string roman = "";

            int decimalPlace = 0;   // Start at 10^0 (ones place)
            while (arabic > 0)
            {
                // Get lowest digit
                int currentDigit = arabic % 10;

                // Add converted string to output
                RomanDigit digit = RomanDigits[decimalPlace];
                if (currentDigit % 5 == 4)  // Special case for 4 and 9, print "One" followed by "Five" or "Ten".
                    roman = string.Format("{0}{1}", digit.One, (currentDigit == 9) ? digit.Ten : digit.Five) + roman;
                else // If currentDigit > 5, print "Five". Then print "One" several times until done.
                    roman = string.Format("{0}{1}", (currentDigit >= 5) ? digit.Five.ToString() : "", new String(digit.One, currentDigit % 5)) + roman;

                // Next loop iteration
                arabic /= 10;    // Divide by 10 to get next digit
                decimalPlace++;  // Go to next RomanDigit
            }

            return roman;
        }
    }