asp.net生成验证码

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.Text;
public partial class AJAX_RandomJpgSample : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (Session["MyCheckCode"] == null)
            Session["MyCheckCode"] = "";
        GenerateCheckCode();
    }
    /// <summary>
    /// 产生随机数
    /// </summary>
    /// <returns></returns>
    private void GenerateCheckCode()
    {
        StringBuilder strS = new StringBuilder();
        string strTmp = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
char[] str = strTmp.ToCharArray();
        //string[] str ={ "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "0", "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z" };
        Random rn = new Random();
        int len = rn.Next(4, 6); //随即生成4或5,用来控制验证码的长度
        Random ran = new Random();
        //设置图片输出格式
        Response.ContentType = "image/gif";
        Bitmap b = new Bitmap(85, 28);
        Graphics g = Graphics.FromImage(b);
        g.FillRectangle(new SolidBrush(Color.YellowGreen),0,0,140,30);
        Font font = new Font(FontFamily.GenericSansSerif, 18, FontStyle.Bold, GraphicsUnit.Pixel);
        for (int i = 0; i < len; i++)
        {
            strS.Append(str[ran.Next(0,35)]);
            //绘出生成的随机数
            g.DrawString(strS[strS.Length - 1].ToString(), font, new SolidBrush(Color.Blue), i * 15, ran.Next(0, 4));
        }
        //生成干扰条
        Pen pen = new Pen(new SolidBrush(Color.Blue), 1);
        for (int i = 0; i < 10; i++)
        {
            g.DrawLine(pen, new Point(ran.Next(0, 199), ran.Next(0, 59)), new Point(ran.Next(0, 199), ran.Next(0, 15)));
        }
        b.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Gif);
        this.Session["MyCheckCode"] = strS.ToString();
        Response.End();
    }
    /// <summary>
    /// 客户端验证用户输入验证码是否正确
    /// </summary>
    /// <param name="checkCode"></param>
    /// <returns></returns>
    public static bool CheckCode(string checkCode)
    {
        string txt = System.Web.HttpContext.Current.Session["MyCheckCode"] as string;
        return checkCode == txt;
    }
}

客户端使用.aspx
<img id="img4" src="RandomJpgSample.aspx" onclick="javascript:this.src='RandomJpgSample.aspx?'+Math.random()" |"ShowNew()"/>
.aspx.cs
if (AJAX_RandomJpgSample.CheckCode(trace.Text.Trim()))
            Response.Write("验证通过");
因为web窗体(包括.aspx和.aspx.cs文件，其中.aspx继承自.aspx.cs)是一个类，所以在其它窗体可以直接使用类名调用其静态方法，但是没有IDE的智能提示支持。
单击图片刷新验证码
<script type="Text/javascript">
    function ShowNew(){
     var img1=document.getElementById("img3");
     img1.src="RandomJpgSam.aspx?"+Math.random();
    }
    </script>
输入一个日期判断是一年中的第几天
void Calc()
{
    int num[2][12]={{31,28,31,30,31,30,31,31,30,31,30,31},{31,29,31,30,31,30,31,31,30,31,30,31}};
    int day,month,year,leap,i,sum=0;
    printf("\nPlease input year,month,day:");
    scanf("%d,%d,%d",&year,&month,&day);
    if(year%400==0||year%4==0&&year%100!=0)
       leap=1;
    else
       leap=0;
    if(month>12||month<0)
    {
       printf("Error\n");
    }
    else
    {
       if(day>num[leap][month-1])
           printf("Error\n");
       else
       {
           for(i=0;i<month-1;i++)
           {
           sum+=num[leap][i];
           }
           sum+=day;
           printf("It is the %dth day of %d\n",sum,year);
       }
    }
}