WinForm 制作一个简单的计算器

 namespace WindowsFormsApplication6
 {
     public partial class Form1 : Form
     {
         //存储上次点击了什么按钮，0代表什么都没有点击，1代表数字按钮，2代表点击了运算符
         private int prev = ;
         //存储计算的中间结果
         private decimal zjjg = ;
         //记录上次按得什么运算符
         private string prevysf = "+";

         public Form1()
         {
             InitializeComponent();
         }

         private void button1_Click(object sender, EventArgs e) //输入的数
         {
             //将事件源转换为按钮
             Button btn = sender as Button;
             //替换(文本框内容为0，点击了运算符)
             if (prev ==  || txtbottom.Text == "")
             {
                 txtbottom.Text = btn.Text;
             }
             //追加(内容不为0，并且上次没有点击运算符)
             else
             {
                 txtbottom.Text += btn.Text;
             }
             //点击了按钮数字
             prev = ;
         }

         private void button4_Click(object sender, EventArgs e) //加减乘除
         {
             //事件源转换为按钮
             Button btn = sender as Button;
             //上次按了数字
             if (prev == )
             {
                 txttop.Text += txtbottom.Text + btn.Text;//进行显示拼接
                 switch (prevysf)
                 {
                     case "+":
                         zjjg = zjjg + Convert.ToDecimal(txtbottom.Text); //计算上次运行的结果
                         break;
                     case "-":
                         zjjg = zjjg - Convert.ToDecimal(txtbottom.Text); //计算上次运行的结果
                         break;
                     case "*":
                         zjjg = zjjg * Convert.ToDecimal(txtbottom.Text); //计算上次运行的结果
                         break;
                     case "/":
                         zjjg = zjjg / Convert.ToDecimal(txtbottom.Text); //计算上次运行的结果
                         break;
                 }

                 txtbottom.Text = zjjg.ToString();
             }
             //上次按了运算符
             else
             {

                 if (txttop.Text != "")
                 {
                     string s = txttop.Text;
                     s = s.Substring(, s.Length - );
                     s = s + btn.Text;
                     txttop.Text = s;
                 }
                 else
                 {

                     txttop.Text = txtbottom.Text + btn.Text;
                 }
             }
             //点击了运算符
             prev = ;
             //记录下运算符
             prevysf = btn.Text;
         }

         private void button9_Click(object sender, EventArgs e) //清空
         {
             txttop.Text = "";
             txtbottom.Text = "";
             prevysf = "+";
             prev = ;
             zjjg = ;
         }

         private void button11_Click(object sender, EventArgs e) //等于
         {
             //事件源转换为按钮
             Button btn = sender as Button;
                 switch (prevysf)
                 {
                     case "+":
                         zjjg = zjjg + Convert.ToDecimal(txtbottom.Text); //计算上次运行的结果
                         break;
                     case "-":
                         zjjg = zjjg - Convert.ToDecimal(txtbottom.Text); //计算上次运行的结果
                         break;
                     case "*":
                         zjjg = zjjg * Convert.ToDecimal(txtbottom.Text); //计算上次运行的结果
                         break;
                     case "/":
                         zjjg = zjjg / Convert.ToDecimal(txtbottom.Text); //计算上次运行的结果
                         break;
                 }
                 txtbottom.Text = zjjg.ToString();
                 txttop.Text = "";
                 prevysf = "";
                 prev = ;
         }

         private void button17_Click(object sender, EventArgs e) //回退一个
         {
             string s = txtbottom.Text;
             if (s.Length >)
             {
                 s = s.Substring(, s.Length - );
                 txtbottom.Text = s;
             }
             else if(s.Length==)
             {
                 txtbottom.Text = "";
             }
         }

         private void Form1_Load(object sender, EventArgs e)
         {

         }
     }
 }