if (this.ddlstatus.SelectedValue == "普通用户")
            {
                if (BaseClass.CheckStudent(txtNum.Text.Trim(), txtPwd.Text.Trim()))
                {
                    Session["ID"] = txtNum.Text.Trim();
                    Session["name"] = txtNum.Text.Trim();
                    Response.Cookies["UserloginName"].Value = txtNum.Text.Trim();//Cookies保存用户名

 if (!IsPostBack)
        {
            try
            {

                if (Response.Cookies["UserloginName"].Value != null)
                {
                    //用户曾登录 
                    Session["ID"] = Response.Cookies["UserloginName"].Value; //读取Cookie 
                    Session["name"] = Response.Cookies["UserloginName"].Value; //读取Cookie 
                }
                else
                {
                    //返回登录登录界面 
                    Response.Redirect("../Login.aspx");
                }