<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="计算器._Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
        <title>简单计算器</title>
</head>
<body>
        <form id="form1" runat="server">
        <div>
        <asp:TextBox ID="num1" runat="server" ></asp:TextBox>
        <asp:DropDownList ID="dropdownlist" runat="server">
                <asp:ListItem Value="加号" Selected="True">+</asp:ListItem>
                <asp:ListItem Value="减号">-</asp:ListItem>
                <asp:ListItem Value="乘">*</asp:ListItem>
                <asp:ListItem Value="除">/</asp:ListItem>
        </asp:DropDownList>
        <asp:TextBox ID="num2" runat="server"></asp:TextBox><br/>
                <asp:Label ID="Label1" runat="server" BackColor="#339966" Text="结果是："
                Width="200px"></asp:Label>
                <asp:Button ID="Button1" runat="server" Text="计算" Width="88px"
                        onclick="Button1_Click" />
        </div>
        </form>
</body>
</html>

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;

namespace 计算器
{
        public partial class _Default : System.Web.UI.Page
        {
                protected void Page_Load(object sender, EventArgs e)
                {

                }

                protected void Button1_Click(object sender, EventArgs e)
                {
                        int nu1 = int.Parse(this.num1.Text.ToString());//对nu1从string转为int型。
                        int nu2 = int.Parse(this.num2.Text.ToString());
                        int sum = 0;//对sum进行初始化
                        string n = this.dropdownlist.SelectedItem.Text.ToString();//选择下拉单选框中选择在aspx源中的+，-,*,/。
                                            
                        switch (n)
                        {
                                case ("+"):
                                        sum = nu1 + nu2;
                                        break;
                                case "-":
                                     sum = nu1 - nu2;
                                        break;
                                case "*":
                                     sum = nu1 * nu2;
                                        break;
                                case "/":                                    
                                        sum = nu1 / nu2;
                                        break;
                                default:
                                        Console.WriteLine("请正确输入数字");
                                        break;
                        }
                        this.Label1.Text = sum.ToString();//在空间label中显示sum的值。
                    
                }
        }
}