There are many ways that you could approach this problem. I decided to use lookup tables to make things faster and simpler.
The following code shows a string extension method that converts a Roman numeral string into a long integer:
// Maps letters to numbers.private static Dictionary<char, long> LetterValues = null;// Convert Roman numerals into an integer.public static long ToArabic(this string roman){ // Initialize the letter lookup table if // it hasn't been initialized yet. if (LetterValues == null) { LetterValues = new Dictionary<char, long>(); LetterValues.Add('I', 1); LetterValues.Add('V', 5); LetterValues.Add('X', 10); LetterValues.Add('L', 50); LetterValues.Add('C', 100); LetterValues.Add('D', 500); LetterValues.Add('M', ...
