namespace 练习5
{
    public partial class Form1 : Form
    {
        private int cishu = 0;
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string name = textBox1.Text;
            string pass = textBox2.Text;
           //admin不区分大小写！ name.Equals("admin",StringComparison.OrdinalIgnoreCase)
            if (name.Equals("admin", StringComparison.OrdinalIgnoreCase) && pass == "8888")
            {
                MessageBox.Show("恭喜你,登录成功");

               
            }
            else
            {
                cishu++;//cishu要做成private int cishu; 局部变量是没有用的！
                if (cishu > 3)

                {
                    MessageBox.Show("错误次数过多，程序结束");
                   
                    Application.Exit();//关闭程序代码 用this.close();也可以
                }
                MessageBox.Show("你输入的信息不正确,登录失败.");
            }

 
        }

        private void button2_Click(object sender, EventArgs e)
        {
            this.Close();
        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {

        }
    }
}

怎么能把name 和pass信息用邮件发送到邮箱里去呢？？？

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

using

 private void sende_mail()
    {
        MailMessage mms = new MailMessage();
        mms.Body = "邮件内容";
        mms.Subject = "邮件标题";
        mms.IsBodyHtml = true;
        mms.Attachments.Add(new Attachment("附件路径"));//可以不写
        mms.From = new MailAddress("发件人邮箱");
        mms.To.Add(new MailAddress("收件人邮箱"));
        SmtpClient p = new SmtpClient();
        p.Host = "smtp服务器";//例如126邮箱就用smtp.
        p.Credentials = new ("发件人邮箱的用户名", "发件人邮箱的密码");
        p.Send(mms);
    }

我用的visual 2008编的，报错里面没有 mailmessage这个方法呀

这个功能其实很简单，我在这里看到过http://www.邮件群发功能的源代码，你可以去下载来看看