winform 计算器

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 sitianzuoye5
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            textBox1.Text += button1.Text;
        }

        private void button2_Click(object sender, EventArgs e)
        {
            textBox1.Text += button2.Text;
        }

        private void button3_Click(object sender, EventArgs e)
        {
            textBox1.Text += button3.Text;
        }

        private void button4_Click(object sender, EventArgs e)
        {
            textBox1.Text += button4.Text;
        }

        private void button5_Click(object sender, EventArgs e)
        {
            textBox1.Text += button5.Text;
        }

        private void button6_Click(object sender, EventArgs e)
        {
            textBox1.Text += button6.Text;
        }

        private void button7_Click(object sender, EventArgs e)
        {
            textBox1.Text += button7.Text;
        }

        private void button8_Click(object sender, EventArgs e)
        {
            textBox1.Text += button8.Text;
        }

        private void button9_Click(object sender, EventArgs e)
        {
            textBox1.Text += button9.Text;
        }

        private void button10_Click(object sender, EventArgs e)
        {
            textBox1.Text += button10.Text;
        }

        private void button12_Click(object sender, EventArgs e)
        {
            textBox1.Text += button11.Text;
        }

        private void button13_Click(object sender, EventArgs e)
        {
            textBox1.Text += button12.Text;
        }

        private void button14_Click(object sender, EventArgs e)
        {
            textBox1.Text += button13.Text;
        }

        private void button15_Click(object sender, EventArgs e)
        {
            textBox1.Text += button14.Text;
        }

        private void button16_Click(object sender, EventArgs e)
        {
            textBox1.Text += button15.Text;
        }

        private void button16_Click_1(object sender, EventArgs e)
        {
          
            int a=textBox1.Text.IndexOf("+");
            int b=textBox1.Text.IndexOf("-");
            int c=textBox1.Text.IndexOf("*");
            int d=textBox1.Text.IndexOf("/");
            if (a != -1) {
                textBox1.Text = (Convert.ToDouble(textBox1.Text.Substring(0, a)) + Convert.ToDouble(textBox1.Text.Substring(a + 1))).ToString();
            }
            if (b != -1)
            {
                textBox1.Text = (Convert.ToDouble(textBox1.Text.Substring(0, b)) - Convert.ToDouble(textBox1.Text.Substring(b + 1))).ToString();
            }
            if (c != -1)
            {
                textBox1.Text = (Convert.ToDouble(textBox1.Text.Substring(0, c)) * Convert.ToDouble(textBox1.Text.Substring(c + 1))).ToString();
            }
            if (d != -1)
            {
                textBox1.Text = (Convert.ToDouble(textBox1.Text.Substring(0, d)) / Convert.ToDouble(textBox1.Text.Substring(d + 1))).ToString();
            }

        }
    }
}