PHP login system

1

Hi everyone

I have developed a php login system within the header page of a website.

Everything works fine (wont log in unless username and passwords match etc).

The one problem I have is that if I click on another link inside the header page that opens up a new php file (this new php includes the header file), the log in system resets itself and therefore the user will have to log in again.

here is the code:


<?

// PHP code section
require_once("includes/connect.php");

session_start();
//if(isset($_POST["username"]) && $_POST["username"] != "") {

   $username = $_POST["username"];
   $password = $_POST["password"];

//}
   ?>
   
   
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
   "http://www.w3.org/TR/html4/loose.dtd">
<html>

<head>

<title>DVD Haven</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">

<link rel="stylesheet" type="text/css" href="styles.css">

<script type="text/javascript" src="script.js"></script>

</head>



<body>

<table  border="0" align="center" width="800" cellspacing="0" cellpadding="0">

   <tr> 
       <td colspan="7"><a href="assignment01.html"><img src="header.jpg" height="84" width="800" alt="header" border="0" title="Go to Home Page"/></a></td>
   </tr>

   <!-- Menu -->
   <tr class="menu">
       <td><a href="products.php" onmouseover="menu('products','Over')" onmouseout="menu('products','Norm')">
           <img name="products" src="images/products.jpg" width="103" height ="36" alt="products" border="0"/></a>
       </td>
       
       <td><a href="reviews.php" onmouseover="menu('reviews','Over')" onmouseout="menu('reviews','Norm')">
           <img name="reviews" src="images/reviews.jpg" width="91" height ="36" alt="reviews" border="0" /></a>
       </td>

       <td><a href="register.php" onmouseover="menu('register','Over')" onmouseout="menu('register','Norm')">
           <img name="register" src="images/register.jpg" width="93" height ="36" alt="register" border="0" /></a>
       </td>
       
       <td><a href="stores.php" onmouseover="menu('stores','Over')" onmouseout="menu('stores','Norm')">
           <img name="stores" src="images/stores.jpg" width="82" height ="36" alt="stores" border="0" /></a>
       </td>
       <td width="431" height="36" align="right" class="loginText">
       
       
          <?   
            $query = "SELECT * FROM regouser WHERE username='$username' AND password='$password'";
              $result = mysql_query($query);
            $num_records = mysql_num_rows($result);
               
            if($num_records != 1) {
            ?>
            
            <form name="login" method="post" action="<? echo $_SERVER['PHP_SELF']; ?>">
            <input type="text" name="username" size="10" value="">
            <input type="password" name="password" size="10" value="">
            <input type="submit" value="Login" class="button">
            </form>
            
            <?
            }else{
            
            echo "Thankyou, " . $username = $_POST["username"] . ", you are now logged in.";
            ?>
            
            <form name="logout" method="post" action="#">
            <input type="button" value="Logout" class="button" onclick="javascript:window.location = 'includes/logout.php'">
            </form>
            
            <?
            }
            ?>

            </td>