我在Visual Studio 2013上的C#代码；工作不正常

我正在努力成为一个受过教育的懒惰化学学生，通过制作一个可以为我做化学计算的C#程序。为了制作代码，我必须很好地理解化学课上的程序。

我对任何编程都是新手，C#是我的第一语言。该代码适用于1元素计算，但不适用于2元素计算。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApplication8
{
    class Program
    {
        static void Main(string[] args)
        {
            MassCalculation myMassCalculation = new MassCalculation();
            TwoMassCalculation myTwoMassCalculation = new TwoMassCalculation();

            Console.WriteLine("How many elements are in the compound?");
            string userMainInput = Console.ReadLine();

            if (userMainInput == "1")
            {
                myMassCalculation.Amount1 = 1;
                Console.WriteLine("What is the ELEMENT?");
                string userInput1 = Console.ReadLine();
                Elements element;
                if (Enum.TryParse<Elements>(userInput1, true, out element))
                {
                    switch (element)
                    {
                        case Elements.Na:
                            myMassCalculation.Element1 = 22.990;
                            break;
                        case Elements.Cl:
                            myMassCalculation.Element1 = 35.453;
                            break;
                        default:
                            break;
                    }
                }
                Console.WriteLine("How many?");
                string userAmount1 = Console.ReadLine();
                int myAmount1 = int.Parse(userAmount1);
                myMassCalculation.Amount1 = myAmount1;
                myMassCalculation.DoCalculation();
                resultOfMassCalculation(myMassCalculation);
            }
            if (userMainInput == "2")
            {
                Console.WriteLine("What is the First ELEMENT?");
                string userInput1 = Console.ReadLine();
                Elements element;
                if (Enum.TryParse<Elements>(userInput1, true, out element))
                {
                    switch (element)
                    {
                        case Elements.Na:
                            myMassCalculation.Element1 = 22.990;
                            break;
                        case Elements.Cl:
                            myMassCalculation.Element1 = 35.453;
                            break;
                        default:
                            break;
                    }   
                }
                Console.WriteLine("How many?");
                string userAmount1 = Console.ReadLine();
                int myAmount1 = int.Parse(userAmount1);
                myMassCalculation.Amount1 = myAmount1;

                Console.WriteLine("What is the Second ELEMENT?");
                string userInput2 = Console.ReadLine();
                if (Enum.TryParse<Elements>(userInput2, true, out element))
                {
                    switch (element)
                    {
                        case Elements.Na:
                            myTwoMassCalculation.Element2 = 22.990;
                            break;
                        case Elements.Cl:
                            myTwoMassCalculation.Element2 = 35.453;
                            break;
                        default:
                            break;
                    }
                }
                Console.WriteLine("How many?");
                string userAmount2 = Console.ReadLine();
                int myAmount2 = int.Parse(userAmount2);
                myTwoMassCalculation.Amount2 = myAmount2;
                myTwoMassCalculation.DoCalculation();
                resultOfMassCalculation(myTwoMassCalculation);
            }

            Console.ReadLine();
        }
        private static void resultOfMassCalculation(MassCalculation calculation)
        {
            Console.Write("The Mass is {0}g/mol", calculation.DoCalculation());
        }
    }
    enum Elements
    {
        Na,
        Cl,
    }

    class MassCalculation
    {
        public double Element1 { get; set; }
        public int Amount1 { get; set; }
        public virtual double DoCalculation()
        {
            double result = Element1 * Amount1;
            return result;
        }
    }
    class TwoMassCalculation : MassCalculation
    {
        public double Element2 { get; set; }
        public int Amount2 { get; set; }
        public override double DoCalculation()
        {
            double result = Element1 * Amount1 + Element2 * Amount2;
            return result;
        }
    }
}

请帮忙！我知道这看起来有点不专业。我一周前刚开始编程，这是我能做的最好的事情。我需要指导。

代码中唯一定义的元素是Na和Cl，我正在尝试计算NaCl。当一切就绪后，我将向列表中添加更多元素，以及更多不同类型的计算。

我会采纳建设性的意见。

事先非常感谢。