菜鸟必知smarty写登陆

<?php

require("./libs/Smarty.class.php");
$tpl=new Smarty;
$tpl->template_dir='./templates';
$tpl->compile_dir='./templates_c';
$tpl->left_delimiter='<{';
$tpl->right_delimiter='}>';
$tpl->config_dir='configs';

mysql_connect("localhost","root","123");
mysql_select_db("lyb");
$user=@$_POST['username'];
$pw=@$_POST['pass'];
$sql="select * from user where name='".$user."'";
$result=mysql_query($sql);
$res=mysql_fetch_assoc($result);
$pass=$res["password"];


if($res!=""){
if($pw==$pass){
$alert="登陆成功";
}else{
$alert="密码错误";
}
}else{
$alert="用户为空";
}
$tpl->assign("alert",$alert);
$tpl->display("a.html");






?>