Untitled

<?php

include 'config.php';

$session_username = $_SESSION['username'];

if ($_POST['login'])
{
   //get form data
   $username = ($_POST['username']);
   $password = ($_POST['password']);

   if (!$username||!$password)
      echo "Enter a username and password";
   else
   {
    //log in
    $login = mysql_query("SELECT * FROM users WHERE username='$username'");
    if (mysql_num_rows($login)==0)
       echo "No such user";
    else
    {
      while ($login_row = mysql_fetch_assoc($login))
      {
       //get database password
       $password_db = $login_row['password'];

        //encrypt form password
       $password = md5($password);

       //check password
       if ($password!=$password_db)
          echo "Incorrect password";

          else
          {
           $_SESSION['username']=$username; //assign session
           header("Location: index.php"); //refresh
          }
       }


    }
   }
}
else
{

  if (isset($session_username))
  {
   echo "You are logged in, $session_username. <a href='logout.php'>Log out</a>";
  }
  else
  {
   ?> <html>
<head><title>Login Page</title>
<link href="login.css" rel="stylesheet" type="text/css" />
</head>
<body>
<div class="wrapper">
<div id="Box1">
 <form action='index.php' method='POST'>
   Username:

   <input type='text' name='username'><p />
   Password:

   <input type='password' name='password'><p />
   <input type='submit' name='login' value='Log in'>
   </form>
  <br />Don't have an account? <a href="regform.html"><b>Register one today</b></a> for free.</div></div>
</body>
</html> <?php
  }

}

?>