（1）Form1窗体设计界面如下：
（2）运算类型的下列列表中包括：加法、减法、乘法、除法、取模共5种操作；初始状态下，选择“加法”运算，当用户更改运算类型时，下面式子中的加号“+”应自动更改为相应的运算符；
（3）当用户在前两个文本框中输入时，最后得到结果的文本框始终是空白状态，注意该文本框是只读的，用户不能更改其值；只有当用户单击确定按钮时，结果文本框中才会显示正确的计算结果；
（4）使用过程中，用户修改运算类型时，三个文本框的内容自动清空；
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 Csharp7_1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void radioButton1_CheckedChanged(object sender, EventArgs e)
{
if (radioButton1.Checked == true)
{
label3.Text = "+";
textBox1.Text = "";
textBox2.Text = "";
textBox3.Text = "";
}
}
private void radioButton2_CheckedChanged(object sender, EventArgs e)
{
if (radioButton2.Checked == true)
{
label3.Text = "-";
textBox1.Text = "";
textBox2.Text = "";
textBox3.Text = "";
}
}
private void radioButton3_CheckedChanged(object sender, EventArgs e)
{
if (radioButton3.Checked == true)
{
label3.Text = "*";
textBox1.Text = "";
textBox2.Text = "";
textBox3.Text = "";
}
}
private void radioButton4_CheckedChanged(object sender, EventArgs e)
{
if (radioButton4.Checked == true)
{
label3.Text = "÷";
textBox1.Text = "";
textBox2.Text = "";
textBox3.Text = "";
}
}
private void radioButton5_CheckedChanged(object sender, EventArgs e)
{
if (radioButton5.Checked == true)
{
label3.Text = "%";
textBox1.Text = "";
textBox2.Text = "";
textBox3.Text = "";
}
}
private void button1_Click(object sender, EventArgs e)
{
if (radioButton1.Checked == true)
{
textBox3.Text = Convert.ToString((int.Parse(textBox1.Text)) + (int.Parse(textBox2.Text)));
}
if (radioButton2.Checked == true)
{
textBox3.Text = Convert.ToString((int.Parse(textBox1.Text)) - (int.Parse(textBox2.Text)));
}
if (radioButton3.Checked == true)
{
textBox3.Text = Convert.ToString((int.Parse(textBox1.Text)) * (int.Parse(textBox2.Text)));
}
if (radioButton4.Checked == true)
{
textBox3.Text = Convert.ToString((double.Parse(textBox1.Text)) / (double.Parse(textBox2.Text)));
}
if (radioButton5.Checked == true)
{
textBox3.Text = Convert.ToString((int.Parse(textBox1.Text)) % (int.Parse(textBox2.Text)));
}
}
}
}
