What wrong with this php script?

programming
1

Anyone?


<? 
session_start(); 
header("Cache-control: private"); 

if((!$_SESSION['user_name'] === "") || (!$_SESSION['first_name'] === "") || (!$_SESSION['last_name'] === "")) { 
    echo "You must login to post! If you do not have an account you may register it for free!"; 
    include 'login.html'; 
    include 'signup.html'; 
    exit(); 
} 

else {
include 'db.php'; 
$title = $_POST['title']; 
$url = $_POST['url']; 
$message = $_POST['message']; 
$username = $_SESSION['user_name'];
$firstname = $_SESSION['first_name'];
$lastname = $_SESSION['last_name'];

$title = stripslashes($title); 
$url = stripslashes($url); 
$message = stripslashes($message); 

if ((!$title) || (!$url) || (!$message) || (!$username) || (!$firstname) || (!$lastname)) { 
    echo 'Please fill in all fields!'; 
}

$sql = mysql_query("INSERT INTO public (title, url, message, username, firstname, lastname, postdate) 
        VALUES('$title', '$url', '$message', '$username', '$firstname', '$lastname', 'now()')") 
}
?>