C#--，设计一个windows应用程序，实现不同运算。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            comboBox1.Items.Add("+");
            comboBox1.Items.Add("-");
            comboBox1.Items.Add("*");
            comboBox1.Items.Add("/");

            comboBox1.SelectedIndex = 0;

        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (comboBox1.Text == "+")
            {

                double x = double.Parse(textBox1.Text);

                double y = double.Parse(textBox2.Text);

                textBox3.Text = (x + y).ToString();
            }

            if (comboBox1.Text == "-")
            {
                double x = double.Parse(textBox1.Text);

                double y = double.Parse(textBox2.Text);

                textBox3.Text = (x - y).ToString();
            }

            if (comboBox1.Text == "*")
            {
                double x = double.Parse(textBox1.Text);

                double y = double.Parse(textBox2.Text);

                textBox3.Text = (x * y).ToString();
            }

            if (comboBox1.Text == "/")
            {
                double x = double.Parse(textBox1.Text);

                double y = double.Parse(textBox2.Text);

                textBox3.Text = (x/y).ToString();
            }
        }

      

      
    }
}