Untitled

<?php
session_start();
if (isset($_GET['logout'])){
    unset($_SESSION['logged_in']);
}
?>
<html>
    <head>
        <title>Database login</title>
        <?php
        if (isset($_POST['submit'])) {
            //print_r($_POST);
            $password = md5($_POST['password']);
            //echo'<p>'.$password.'</p>';
            $username = ($_POST['username']);
            //echo'<p>'.$username.'</p>';
        }
        $db = new PDO('sqlite:login.sqlite');
        $login = 'SELECT * FROM login
        WHERE userid="'.$username.'"
        AND password="'.$password.'";';
        //echo'<p>'.$login.'</p>';
        $attempt = $db->query($login);
        foreach ($attempt as $row) {
        //print_r($row);
        $_SESSION['logged_in'] = $username;
        }
        ?>
    </head>
    <body>
        <?php
        if (!isset($_SESSION['logged_in'])){
        ?>
            <form method="post" action="Db_login.php">
            <p>Username:<br /><input type="text" name="username" /> </p>
            <p>Password:<br /><input type="password" name="password" /></p>
            <p><input type="submit" name="submit" value="Log In!" /></p>
            </form>
        <?php
        } else {
        ?>
        <h1> Protected Content!</h1>
        <p>You are logged in as <em><?php echo $_SESSION['logged_in']; ?> </em></p>
        <p><a href="Db_login.php?logout=true">Log out!</a></p>
        <p><a href="Db_new_Cars.php">Add a new car</a></p>
        <p><a href="">Book out a car</a></p>
        <A HREF="javascript:alert('Your resolution is '+screen.width+'x'+screen.height);">
        Screen resolution finder!</A>
            <?php

        $pre = $_SERVER ['HTTP_USER_AGENT'];
        if(strpos($pre,"Firefox")!=0)
        $browser = "Firefox";
        else if (strpos($pre,"Safari")!=0)
        $browser = "Safari";
        else if (strpos($pre,"MSIE")!=0)
        $browser = "Internet Explorer";
        else if(strpos($pre,"Presto")!=0)
            $browser = "Opera";
        else $browser = "Unknown";
    echo '<p>Your browser is: '.$browser.'</p>';
    ?>


        <?php
        }
        ?>
    </body>
</html>