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 = "";            }        }    }}