asp.net网站根据用户注册信息完成登录示例
 protected void btnLoad_Click(object sender, ImageClickEventArgs e)
    {
        HttpCookie cookie = Request.Cookies["CheckCode"];
        if (String.Compare(cookie.Value, txtVali.Text, true) != 0)
        {            Response.Write("<script lanuage=javascript>alert('验证码错误');location='javascript:history.go(-1)'</script>");
        }        else
        {
           DataSet ds = DB.reDs("select * from tb_HuenLian where UserName='" + txtUid.Text.Trim() + "' and PassWord='" + txtPwd.Text.Trim() + "'");
            int i = this.checkLogin(txtUid.Text, txtPwd.Text);
            if (i > 0)
            {
                Session["id"] = ds.Tables[0].Rows[0][0].ToString();
                Session["UserName"] = this.txtUid.Text;
                Session["PassWord"] = this.txtPwd.Text;
                Page.Response.Redirect("login.aspx");//登录成功登录该网页
            }
            else
            {
                Response.Write("<script lanuage=javascript>alert('用户名称或密码错误!');location='javascript:history.go(-1)'</script>");
            }
        }
    }//codego.net/tags/11/1/
    public int checkLogin(string loginName, string loginPwd)
    {
        SqlConnection con = new SqlConnection(ConfigurationManager.AppSettings["conn"]);
        SqlCommand myCommand = new SqlCommand("select count(*) from tb_HuenLian where UserName=@loginName and PassWord=@loginPwd", con);
        myCommand.Parameters.Add(new SqlParameter("@loginName", SqlDbType.NVarChar, 20));
        myCommand.Parameters["@loginName"].Value = loginName;
        myCommand.Parameters.Add(new SqlParameter("@loginPwd", SqlDbType.NVarChar, 50));
        myCommand.Parameters["@loginPwd"].Value = loginPwd;
        myCommand.Connection.Open();
        int i = (int)myCommand.ExecuteScalar();
        myCommand.Connection.Close();
        return i;
    }