[Php] Login systeem

<?php
mysql_connect('192.168.0.11','databasenaam','databasewachtwoord') or die("couldn't connect to the database. Please try again.");
mysql_select_db('u56452099') or die(mysql_error());
session_start(); 
if(isset($_POST['login'])) {
  if(trim($_POST['loginnaam']) != "" && trim($_POST['wachtwoord']) != "") {
    
    
    $naam  = $_POST['loginnaam'];
    $wacht = md5($_POST['wachtwoord']);
    $res1 = mysql_query("SELECT id, password, status FROM users where username='".$naam."'") or die(mysql_error());

    
    if(mysql_num_rows($res1) > 0) {
      $row = mysql_fetch_assoc($res1);
      if(!strcmp($wacht, $row['password'])) {
        $_SESSION['user']    = $naam;         // gebruikersnaam van ingelogd persoon
        $_SESSION['level']   = $row['level']; // bijbehorende gebruikersniveau
        $_SESSION['time']    = time();        // de huidige tijd
        $_SESSION['maxidle'] = 60*30;       // het aantal seconden inactiviteit
      } else {
        
        $_SESSION = array();
        session_destroy();
      }
      unset($row);
      mysql_free_result($res1);
    }
    
    header("Location: calculation.php");
  }
}



if(isset($_POST['logout']))
{
$_SESSION = array(); 
session_destroy(); 
header("Location: calculation.php");  
}

if(!isset($_SESSION['user'])) {
?>

<?php
mysql_connect('192.168.0.11','databasenaam','databasewachtwoord') or die("couldn't connect to the database. Please try again.");
mysql_select_db('u56452099') or die(mysql_error());
session_start(); 
if(isset($_POST['login'])) {
  if(trim($_POST['loginnaam']) != "" && trim($_POST['wachtwoord']) != "") {
 
 
    $naam  = $_POST['loginnaam'];
    $wacht = md5($_POST['wachtwoord']);
    $res1 = mysql_query("SELECT id, password, status FROM users where username='".$naam."'") or die(mysql_error());
 
 
    if(mysql_num_rows($res1) > 0) {
      $row = mysql_fetch_assoc($res1);
      if(!strcmp($wacht, $row['password'])) {
        $_SESSION['user']    = $naam;         // gebruikersnaam van ingelogd persoon
        $_SESSION['level']   = $row['level']; // bijbehorende gebruikersniveau
        $_SESSION['time']    = time();        // de huidige tijd
        $_SESSION['maxidle'] = 60*30;       // het aantal seconden inactiviteit
      } else {
 
        $_SESSION = array();
        session_destroy();
      }
      unset($row);
      mysql_free_result($res1);
    }
 
    header("Location: calculation.php");
  }
}
 
 
 
if(isset($_POST['logout']))
{
$_SESSION = array(); 
session_destroy(); 
header("Location: calculation.php");  
}
 
if(!isset($_SESSION['user'])) {
?>

<?php
} else {
$now = time();
if($now - $_SESSION['time'] > $_SESSION['maxidle']) {
    $_SESSION = array();
    session_destroy();
  } else {
$_SESSION['time'] = $now;
  }

?>

<?php
} else {
$now = time();
if($now - $_SESSION['time'] > $_SESSION['maxidle']) {
    $_SESSION = array();
    session_destroy();
  } else {
$_SESSION['time'] = $now;
  }
 
?>

<? 
}
?>

<? 
}
?>