using System;

using System.Collections.Generic;

using System.Linq;

​

public static class Program

{

    public static void Main()

    {

        Console.WriteLine(312.ToRoman());

    }

}

​

public static class Extensions

{

    // http://stackoverflow.com/questions/7040289/converting-integers-to-roman-numerals

    // http://stackoverflow.com/questions/14900228/roman-numbers-to-integers

    public static string ToRoman(this int number)

    {

            var romanMap = new Dictionary<string, int>

            {

               {"M", 1000}, {"CM", 900}, {"D", 500}, {"CD", 400}, {"C", 100}, {"XC", 90}, {"L", 50}, {"XL", 40}, {"X", 10}, {"IX", 9}, {"V", 5}, {"IV", 4}, {"I", 1}

            };

        if ((number < 0) || (number > 3999))

            throw new ArgumentOutOfRangeException("insert value betwheen 1 and 3999");

        if (number < 1)

            return string.Empty;

        foreach (var pair in romanMap.Where(pair => number >= pair.Value))

        {

            return pair.Key + ToRoman(number - pair.Value);

        }

​

        throw new ArgumentOutOfRangeException("something bad happened");

    }

}