大家来看看我这个计算器代码

下面是我做的计算器  我要怎么样才能实现连加、减、乘、除呢。现在能实现普通功能了
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 jisuanqi
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }        public string number;
        public int OperationType;//适用于计算的类型，应用数字去控制算法
        public double number1, number2;//number1后台存储, number2前台存储        private void btn1_Click(object sender, EventArgs e)
        {
            if (txtbox.Text == "0")
            {
                number = "1";
                txtbox.Text = Convert.ToString(number);
            }
            else
            {
                number = number + "1";
                number2 = Convert.ToDouble(number);
                txtbox.Text = number;
            }        }        private void btn2_Click(object sender, EventArgs e)
        {
            if (txtbox.Text == "0")
            {
                number = "2";
                txtbox.Text = Convert.ToString(number);
            }
            else
            {
                number = number + "2";
                number2 = Convert.ToDouble(number);
                txtbox.Text = number;
            }
        }        private void btn3_Click(object sender, EventArgs e)
        {
            if (txtbox.Text == "0")
            {
                number = "3";
                txtbox.Text = Convert.ToString(number);
            }
            else
            {
                number = number + "3";
                number2 = Convert.ToDouble(number);
                txtbox.Text = number;
            }
        }        private void btn4_Click(object sender, EventArgs e)
        {
            if (txtbox.Text == "0")
            {
                number = "4";
                txtbox.Text = Convert.ToString(number);
            }
            else
            {
                number = number + "4";
                number2 = Convert.ToDouble(number);
                txtbox.Text = number;
            }
        }        private void btn5_Click(object sender, EventArgs e)
        {
            if (txtbox.Text == "0")
            {
                number = "5";
                txtbox.Text = Convert.ToString(number);
            }
            else
            {
                number = number + "5";
                number2 = Convert.ToDouble(number);
                txtbox.Text = number;
            }
        }        private void btn6_Click(object sender, EventArgs e)
        {
            if (txtbox.Text == "0")
            {
                number = "6";
                txtbox.Text = Convert.ToString(number);
            }
            else
            {
                number = number + "6";
                number2 = Convert.ToDouble(number);
                txtbox.Text = number;
            }
        }        private void btn7_Click(object sender, EventArgs e)
        {
            if (txtbox.Text == "0")
            {
                number = "7";
                txtbox.Text = Convert.ToString(number);
            }
            else
            {
                number = number + "7";
                number2 = Convert.ToDouble(number);
                txtbox.Text = number;
            }
        }        private void btn8_Click(object sender, EventArgs e)
        {
            if (txtbox.Text == "0")
            {
                number = "8";
                txtbox.Text = Convert.ToString(number);
            }
            else
            {
                number = number + "8";
                number2 = Convert.ToDouble(number);
                txtbox.Text = number;
            }
        }        private void btn9_Click(object sender, EventArgs e)
        {
            if (txtbox.Text == "0")
            {
                number = "9";
                txtbox.Text = Convert.ToString(number);
            }
            else
            {
                number = number + "9";
                number2 = Convert.ToDouble(number);
                txtbox.Text = number;
            }
        }        private void btn0_Click(object sender, EventArgs e)
        {
            if (txtbox.Text == "0")
            {
                number = "0";
                txtbox.Text = Convert.ToString(number);
            }
            else
            {
                number = number + "0";
                number2 = Convert.ToDouble(number);
                txtbox.Text = number;
            }
        }        private void btnspot_Click(object sender, EventArgs e)
        {
            if (txtbox.Text == "0")
            {
                number = "0.";
                txtbox.Text = Convert.ToString(number);
            }
            else
            {
                number = number + "0.";
                number2 = Convert.ToDouble(number);
                txtbox.Text = number;
            }
        }
        /// <summary>
        /// 清除
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnclear_Click(object sender, EventArgs e)
        {
            number = "";
            txtbox.Text = "0";
        }        /// <summary>
        /// 加
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnadd_Click(object sender, EventArgs e)
        {
            OperationType = 1;
            if (txtbox.Text.Length > 0)
            {
                number1 = Convert.ToDouble(txtbox.Text);
                number = "";
            }
        }        /// <summary>
        /// 减
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnSubtration_Click(object sender, EventArgs e)
        {
            OperationType = 2;
            if (txtbox.Text.Length > 0)
            {
                number1 = Convert.ToDouble(txtbox.Text);
                number = "";
            }
        }        /// <summary>
        /// 乘以
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnMultiplication_Click(object sender, EventArgs e)
        {
            OperationType = 3;
            if (txtbox.Text.Length > 0)
            {
                number1 = Convert.ToDouble(txtbox.Text);
                number = "";
            }
        }        /// <summary>
        /// 除以
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnDivision_Click(object sender, EventArgs e)
        {
            OperationType = 4;
            if (txtbox.Text.Length > 0)
            {
                number1 = Convert.ToDouble(txtbox.Text);
                number = "";
            }
        }        /// <summary>
        /// 等于
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btnequal_Click(object sender, EventArgs e)
        {
            switch (OperationType)
            {
                case 1:                    txtbox.Text = Convert.ToString(number1 + Convert.ToDouble(txtbox.Text));
                    number2 = Convert.ToDouble(txtbox.Text);
                    break;
                case 2:                    txtbox.Text = Convert.ToString(number1 - Convert.ToDouble(txtbox.Text));
                    number2 = Convert.ToDouble(txtbox.Text);
                    break;
                case 3:                    txtbox.Text = Convert.ToString(number1 * Convert.ToDouble(txtbox.Text));
                    number2 = Convert.ToDouble(txtbox.Text);
                    break;
                case 4:
                    if (txtbox.Text == "0")
                    {
                        txtbox.Text = "0";
                    }
                    else
                    {
                        txtbox.Text = Convert.ToString(number1 / Convert.ToDouble(txtbox.Text));
                        number2 = Convert.ToDouble(txtbox.Text);
                    }
                    break;            }
            number = "";
            number1 = Convert.ToDouble(txtbox.Text);
        }    }
}