RomanToDecimal.cs

using System;
using System.Collections.Generic;


namespace ConsoleApp161
{
  class Test
  {
    public virtual int value(char r)
    {
      if (r =='I')
        return 1;
      if (r == 'V')
        return 5;
      if (r == 'X')
        return 10;
      if (r == 'L')
        return 50;
      if (r == 'C')
        return 100;
      if (r == 'D')
        return 500;
      if (r == 'M')
        return 1000;
      return -1;
    }

    public virtual int romanTODecimal(string str)
    {
      int res = 0;
      for (int i = 0; i < str.Length; i++)
      {
        int s1 = value(str[i]);
        if (i+1 < str.Length)
        {
          int s2 = value(str[i + 1]);
          if (s1 >=s2)
          {
            res = res + s1;
          }
          else
          {
            res = res + s2 - s1;
            i++;
          }
        }
        else
        {
          res = res + s1;
          i++;
        }
      }

      return res;
    }
  }

  class Program
  {
    public static void Main(string[] args)
    {
      string str = "MCMIV";
      Test test = new Test();
      var t = test.romanTODecimal(str);
      Console.WriteLine(t);
    }

  }
   
}