header.php

<?php
include_once 'admin-panel.php';
session_start();
?>

<!DOCTYPE html>
<html>
<head>
   <title> </title>
   <link rel="stylesheet" type="text/css" href="style.css">
</head>


<body>

<header>
 <nav>
     <div class="main-wrapper">
	      <ul>
	            <li><a href="index.php">home</a></li>
	       </ul>
		       <div class="nav-login">
			       <?php
				        if (isset($_SESSION['u_id'])) {
						  echo '<form action="includes/logout.inc.php" method="POST">
					            <button type="submit" name="submit">logout</button>
					              </form>';	
   
							
			            } else{
							
							echo '<form action="includes/login.inc.php" method="POST">
                              <input type="text" name="uid" placeholder="username/e-mail">
                              <input type="password" name="pwd" placeholder="password">
                               <button type="submit" name="submit">login</button>						
				                </form>
				               <a href="signup.php">signup</a>';
							
						}
				   
				    ?>
					
				
		       </div>
	 </div>
 </nav>

</header>