using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Web;

 /// <summary>
 ///Calculator 的摘要说明
 /// </summary>
 public class Calculator
 {
     //
     //TODO: 在此处添加构造函数逻辑
     //
     ;
     ;

     public double A
     {
         get { return a; }
         set { a = value; }
     }
     public double B
     {
         get { return b; }
         set { b = value; }
     }
     public virtual double GetResult()
     {
         ;
         return result;
     }

 }

 class Add : Calculator
 {
     public override double GetResult()
     {
         ;
         result = A + B;
         return result;
     }
 }

 class Sub : Calculator
 {
     public override double GetResult()
     {
         ;
         result = A - B;
         return result;
     }
 }

 class Mul : Calculator
 {
     public override double GetResult()
     {
         ;
         result = A * B;
         return result;
     }
 }

 class Div : Calculator
 {
     public override double GetResult()
     {
         ;
         )
         throw new Exception("除数不能为0");
         result = A / B;
         return result;
     }
 }

 public class Factory
 {
     public static Calculator Cal(string operate)
     {
         Calculator oper = null;
         switch (operate)
         {
             case "+":
                 oper = new Add();
                 break;
             case "-":
                 oper = new Sub();
                 break;
             case "*":
                 oper = new Mul();
                 break;
             case "/":
                 oper = new Div();
                 break;
         }
         return oper;
     }
 }

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Web;
 using System.Web.UI;
 using System.Web.UI.WebControls;

 public partial class index : System.Web.UI.Page
 {
     protected void Page_Load(object sender, EventArgs e)
     {
         //界面加载
     }
     protected void Cal_Click(object sender, EventArgs e)
     {
         Calculator oper;
         string strOperate = DropDownList1.SelectedItem.ToString();
         oper = Factory.Cal(strOperate);
         oper.A = Convert.ToDouble(TextBox1.Text);
         oper.B = Convert.ToDouble(TextBox2.Text);
         string answer = Convert.ToString(oper.GetResult());

         string result = TextBox1.Text + DropDownList1.SelectedItem.ToString() + TextBox2.Text;//把运算式子存在result里面
         if (TextBox3.Text == answer)                                  //如果输入答案与计算出的answer相等
         {
             Response.Write("<script>alert('回答正确!')</script>");          //弹出回答正确
             ListBox1.Items.Add(result + "=" + TextBox3.Text.Trim() + "√");//并把运算式子存在listbox里
         }

         else                                                          //如果答错
         {
             Response.Write("<script>alert('答题错误!')</script>");           //弹出答题错误
             ListBox1.Items.Add(result + "=" + TextBox3.Text.Trim() + "×");//同样把运算式子放在listbox
         }
         TextBox1.Text = "";//把文本框清空，进行下一次出题
         TextBox2.Text = "";
         TextBox3.Text = "";
     }
 }