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 = "";
}
}
}
}