RomanNumeral

gistfile1.cs

struct RomanNumeral
    {
        static readonly List<RomanNumeral> RomanNumerals;
        readonly int integer;
        readonly string roman;

        static RomanNumeral()
        {
            RomanNumerals = new List<RomanNumeral>
                {
                    new RomanNumeral(1000, "M"),
                    new RomanNumeral(900, "CM"),
                    new RomanNumeral(500, "D"),
                    new RomanNumeral(400, "CD"),
                    new RomanNumeral(100, "C"),
                    new RomanNumeral(90, "XC"),
                    new RomanNumeral(50, "L"),
                    new RomanNumeral(40, "XL"),
                    new RomanNumeral(10, "X"),
                    new RomanNumeral(9, "IX"),
                    new RomanNumeral(5, "V"),
                    new RomanNumeral(4, "IV"),
                    new RomanNumeral(1, "I")
                };
        }

        RomanNumeral(int integer, string roman)
        {
            this.integer = integer;
            this.roman = roman;
        }

        public RomanNumeral(int integer) : this(integer, IntegerToRoman(integer)) {}

        public RomanNumeral(string roman) : this(RomanToInteger(roman), roman) {}

        public static implicit operator int(RomanNumeral romanNumeral)
        {
            return romanNumeral.integer;
        }

        public override string ToString()
        {
            return roman;
        }

        static int RomanToInteger(string roman)
        {
            var integer = 0;
            foreach (var rn in RomanNumerals)
            {
                while (roman.Any())
                {
                    if (!roman.StartsWith(rn.roman))
                        break;
                    integer += rn.integer;
                    roman = roman.Substring(rn.roman.Length);
                }
            }
            return integer;
        }

        static string IntegerToRoman(int i)
        {
            var stringBuilder = new StringBuilder();
            foreach (var rn in RomanNumerals)
            {
                while (i >= rn.integer)
                {
                    i -= rn.integer;
                    stringBuilder.Append(rn.roman);
                }
            }
            return stringBuilder.ToString();
        }
    }