//定義操作數(shù)和結(jié)果
string firstValue, secondValue, result;
char operation;
//存儲上次點(diǎn)擊了什么按鈕，0代表什么都沒點(diǎn)擊，1代表了數(shù)字按鈕
 private int lastButtonStatus = 0;

private void btnVaL_Click(object sender, EventArgs e)
  {
   Button btn = (Button)sender;
   if (lastButtonStatus == 0 || textBox_show.Text == "0")
   {
    textBox_show.Text = btn.Text;
   }
   else
   {
    textBox_show.Text += btn.Text;
   }
   lastButtonStatus = 1;
  }
  //將數(shù)字按鈕的事件集中處理
  private void Form1_Load(object sender, EventArgs e)
  {
   this.textBox_show.Text = "0";
   this.textBox_top.Text = "0";
   btn_0.Click += new EventHandler(btnVaL_Click);
   btn_1.Click += new EventHandler(btnVaL_Click);
   btn_2.Click += new EventHandler(btnVaL_Click);
   btn_3.Click += new EventHandler(btnVaL_Click);
   btn_4.Click += new EventHandler(btnVaL_Click);
   btn_5.Click += new EventHandler(btnVaL_Click);
   btn_6.Click += new EventHandler(btnVaL_Click);
   btn_7.Click += new EventHandler(btnVaL_Click);
   btn_8.Click += new EventHandler(btnVaL_Click);
   btn_9.Click += new EventHandler(btnVaL_Click);
   btn_point.Click += new EventHandler(btnVaL_Click);
  }

//加
  private void btn_add_Click(object sender, EventArgs e)
  {
   firstValue = textBox_show.Text;
   operation = '+';
   textBox_top.Text = firstValue + '+';
   textBox_show.Text = string.Empty;
  }
  //減
  private void btn_sub_Click(object sender, EventArgs e)
  {
   firstValue = textBox_show.Text;
   operation = '-';
   textBox_top.Text = firstValue + '-';
   textBox_show.Text = string.Empty;
  }
  //乘
  private void btn_mult_Click(object sender, EventArgs e)
  {
   firstValue = textBox_show.Text;
   operation = '*';
   textBox_top.Text = firstValue + '*';
   textBox_show.Text = string.Empty;
  }
  //除
  private void btn_div_Click(object sender, EventArgs e)
  {
   firstValue = textBox_show.Text;
   operation = '/';
   textBox_top.Text = firstValue + '/';
   textBox_show.Text = string.Empty;
  }
  //求余
  private void btn_remain_Click(object sender, EventArgs e)
  {
   firstValue = textBox_show.Text;
   operation = '%';
   textBox_top.Text = firstValue + '%';
   textBox_show.Text = string.Empty;
  }
  //求平方和
  private void btn_square_Click(object sender, EventArgs e)
  {
   firstValue = textBox_show.Text;
   textBox_top.Text = firstValue + "的平方是：";
   double outFirst;
   double.TryParse(firstValue, out outFirst);
   textBox_show.Text = (outFirst * outFirst).ToString();
  }
  //求平方根
  private void btn_involution_Click(object sender, EventArgs e)
  {
   firstValue = textBox_show.Text;
   textBox_top.Text = firstValue + "的平方根是：";
   double outFirst;
   double.TryParse(firstValue, out outFirst);
   textBox_show.Text = (Math.Sqrt(outFirst)).ToString();
  } 
  //等號,處理加、減、乘、除、求余、運(yùn)算
  private void btn_equal_Click(object sender, EventArgs e)
  {
   secondValue = textBox_show.Text;
   textBox_top.Text += secondValue + '=';
   double outFirst, outSecond;
   double.TryParse(firstValue, out outFirst);
   double.TryParse(secondValue,out outSecond);
   switch (operation)
   {
    case '+':
     result = (outFirst + outSecond).ToString();
     break;
    case '-':
     result = (outFirst - outSecond).ToString();
     break;
    case '*':
     result = (outFirst * outSecond).ToString();
     break;
    case '/':
     if (outSecond != 0)
     {
      result = (outFirst / outSecond).ToString();
     }
     else
     {
      MessageBox.Show("被除數(shù)不能為0");
     }
     break;
    case '%':
     result = (outFirst % outSecond).ToString();
     break;
   }
   textBox_show.Text = result;
  }

//退格功能
  private void btn_back_Click(object sender, EventArgs e)
  {
   if (textBox_show.Text.Length > 0)
   {
    textBox_show.Text = textBox_show.Text.Substring(0, textBox_show.Text.Length - 1);
   }
  }
  //清空
  private void btn_clear_Click(object sender, EventArgs e)
  {
   textBox_top.Text = string.Empty;
   textBox_show.Text = string.Empty;
   firstValue = string.Empty;
   secondValue = string.Empty;
  }