PhP登录/注册系统

我发现了这个关于使用PhP和MySQL创建登录/注册系统的好教程。该论坛已有5年历史（去年编辑），但仍然可以使用。

初学者简单注册登录系统

登录和注册页面似乎都有问题。

<?php 
function register_form(){ 
$date = date('D, M, Y'); 
echo "<form action='?act=register' method='post'>" 
."Username: <input type='text' name='username' size='30'><br>" 
."Password: <input type='password' name='password' size='30'><br>" 
."Confirm your password: <input type='password' name='password_conf' size='30'><br>" 
."Email: <input type='text' name='email' size='30'><br>" 
."<input type='hidden' name='date' value='$date'>" 
."<input type='submit' value='Register'>" 
."</form>"; 
} 
function register(){ 
$connect = mysql_connect("host", "username", "password"); 
if(!$connect){ 
die(mysql_error());
} 
$select_db = mysql_select_db("database", $connect); 
if(!$select_db){ 
die(mysql_error()); 
} 
$username = $_REQUEST['username']; 
$password = $_REQUEST['password']; 
$pass_conf = $_REQUEST['password_conf']; 
$email = $_REQUEST['email']; 
$date = $_REQUEST['date']; 

if(empty($username)){ 
die("Please enter your username!<br>"); 
} 
if(empty($password)){ 
die("Please enter your password!<br>"); 
} 
if(empty($pass_conf)){ 
die("Please confirm your password!<br>"); 
} 
if(empty($email)){ 
die("Please enter your email!"); 
} 

$user_check = mysql_query("SELECT username FROM users WHERE username='$username'"); 
$do_user_check = mysql_num_rows($user_check); 

$email_check = mysql_query("SELECT email FROM users WHERE email='$email'"); 
$do_email_check = mysql_num_rows($email_check); 

if($do_user_check > 0){ 
die("Username is already in use!<br>"); 
} 
if($do_email_check > 0){ 
die("Email is already in use!"); 
} 

if($password != $pass_conf){ 
die("Passwords don't match!"); 
} 

$insert = mysql_query("INSERT INTO users (username, password, email) VALUES      ('$username', '$password', '$email')"); 
if(!$insert){ 
die("There's little problem: ".mysql_error()); 
} 
echo $username.", you are now registered. Thank you!<br><a href=login.php>Login</a> |     <a href=index.php>Index</a>"; 
} 
switch($act){ 
default; 
register_form(); 
break; 
case "register"; 
register(); 
break; 
} 
?>

一旦按下注册按钮，页面将不起任何作用，字段将被删除，数据库中不会添加任何数据或给出错误。我认为问题可能是switch($act){部分，所以我删除了它，并使用require 更改了页面

require('connect.php');

其中connect.php是

<?php
mysql_connect("localhost","host","password");
mysql_select_db("database");
?>

删除了function register_form(){和echo部分，将其转换为HTML代码：

<form action='register' method='post'> 
Username: <input type='text' name='username' size='30'><br>
Password: <input type='password' name='password' size='30'><br>
Confirm your password: <input type='password' name='password_conf' size='30'><br> 
Email: <input type='text' name='email' size='30'><br> 
<input type='hidden' name='date' value='$date'>
<input type='submit' name="register" value='Register'> 
</form>

我用if($register){ 代替了function register(){

因此，当按下Register按钮时，它会运行php代码，但这种编辑似乎也不起作用。那么问题出在哪里呢？如果需要，我可以在我的域上重新添加此代码

登录页面也有同样的问题，当按下清空字段旁边的按钮时，什么都不会发生。