这里是主要的程序代码部分，请哪位高手指点一下，本人对编程不是很了解，先谢谢了
using System;
using System.Collections.Generic;
using
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace 计算器
{
    public partial class Form1 : Form
    {
        double a { get; set; }
        double b { get; set; }
        double c { get; set; }
        string opt { get; set; }
        public Form1()
        {
            InitializeComponent();
        }

        private void num_Click(object sender, EventArgs e)
        {
            Button btn = (Button)sender;
            this.container.Text += btn.Text;
        }
        private void opt_Click(object sender, EventArgs e)
        {
            a = Convert.ToDouble(this.container.Text);
            Button btn = (Button)sender;
            opt = btn.Text;
            this.container.Text = "";
        }
        private void c_Click(object sender, EventArgs e)
        {
            b = Convert.ToDouble(this.container .Text );
            switch (opt)
            {
                case "+":
                    c = a + b;
                    break;
                case "-": c = a - b;
                    break;
                case "*": c = a * b;
                    break;
                case "/": c = a / b;
                    break;
                case "%": c = a % b;
                    break;
                case "1/x": c = 1 / a;
                    break;
            }
            this.container.Text = c.ToString();








        }
        
        
        
    }
}