一个简单的关于计算器功能的实现（剽窃）

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 标准型ToolStripMenuItem_Click(object sender, EventArgs e)
        {
            MessageBox.Show("标准型");
        }

        private void btnyi_Click(object sender, EventArgs e)
        {
            Button btn = (Button)sender;
            //如果是刚刚点过运算符或者上面输入框是0,那么就把输入框的值赋成刚刚输入的值
            if (isok || txtshuru.Text == "0")
            {
                txtshuru.Text = btn.Text;
            }
            else//否则就累加
            {
                txtshuru.Text += btn.Text;
            }
            isok = false;
        }

        private bool isok = true;//用来记录是否刚刚点过运算符
        private double sum = 0;//存放上一步运算结果
        private string preYunsuanfu = ""; //存放上一步运算符
        private string biaodashi;//存放上面显示的表达式前半部分
        //txtbiaodashi的内容实际上是由成员变量biaodashi与preyunsuanfu组合而成的

        private void btnjia_Click(object sender, EventArgs e)
        {
            if (preYunsuanfu == "")//如果是第一次点运算符
            {
                sum = double.Parse(txtshuru.Text);
                biaodashi = txtshuru.Text;
            }
            else//如果不是第一次点运算符
            {
                //是否刚刚点过运算符
                if (!isok)//如果不是刚刚点过运算符，那么进去运算
                {
                    double shuru = double.Parse(txtshuru.Text);
                    //算结果的话，要根据上一步运算符的符号来算
                    if (preYunsuanfu == "+")
                    {
                        sum = sum + shuru;
                    }

                    if (preYunsuanfu == "-")
                    {
                        sum -= shuru;
                    }

                    if (preYunsuanfu == "*")
                    {
                        sum *= shuru;
                    }

                    if (preYunsuanfu == "/")
                    {
                        sum /= shuru;
                    }
                    if (preYunsuanfu == "%")
                    {
                        sum %= shuru;
                    }
                    //表达式变成了原来表达式+上一步运算符+刚点的输入数字
                    biaodashi = biaodashi + preYunsuanfu + txtshuru.Text;
                }
            }


            txtshuru.Text = sum.ToString();//显示运算结果
            preYunsuanfu = ((Button)sender).Text;//上一步运算符变成刚点的运算符
            txtbiaodashi.Text = biaodashi + preYunsuanfu;//显示式就变成表达式加当点的运算符
            isok = true;//点完运算符把isok设置为true
        }

        private void btnclear_Click(object sender, EventArgs e)
        {
            txtshuru.Text = "0";
            isok = true;
            biaodashi = "";
            sum = 0;
            preYunsuanfu = "";
            txtbiaodashi.Text = "";

        }

        private void btndian_Click(object sender, EventArgs e)
        {
            if (!txtshuru.Text.Contains("."))
            {
                txtshuru.Text += ".";
                isok = false;
            }
        }

        private void btndeng_Click(object sender, EventArgs e)
        {
            if (preYunsuanfu == "")//如果是第一次点运算符
            {
                sum = double.Parse(txtshuru.Text);
                biaodashi = txtshuru.Text;
            }
            else//如果不是第一次点运算符
            {
                //是否刚刚点过运算符
                if (!isok)//如果不是刚刚点过运算符，那么进去运算
                {
                    double shuru = double.Parse(txtshuru.Text);
                    //算结果的话，要根据上一步运算符的符号来算
                    if (preYunsuanfu == "+")
                    {
                        sum = sum + shuru;
                    }

                    if (preYunsuanfu == "-")
                    {
                        sum -= shuru;
                    }

                    if (preYunsuanfu == "*")
                    {
                        sum *= shuru;
                    }

                    if (preYunsuanfu == "/")
                    {
                        sum /= shuru;
                    }
                    if (preYunsuanfu == "%")
                    {
                        sum %= shuru;
                    }
                    //表达式变成了原来表达式+上一步运算符+刚点的输入数字
                    biaodashi = biaodashi + preYunsuanfu + txtshuru.Text;
                }
            }


            txtshuru.Text = sum.ToString();//显示运算结果
            preYunsuanfu = ((Button)sender).Text;//上一步运算符变成刚点的运算符
            if (preYunsuanfu == "=")
            {
                isok = true;
                biaodashi = "";
                sum = 0;
                preYunsuanfu = "";
                txtbiaodashi.Text = "";
            }
        }
    }
}