nav.php

<?php
if(isset($_SESSION["username"])){
?>
    <!-- Navigation -->
    <nav class="navbar fixed-top navbar-expand-lg navbar-dark bg-dark fixed-top">
        <div class="container">
            <a class="navbar-brand" href="index.php">E-Auction</a>
            <button class="navbar-toggler navbar-toggler-right" type="button" data-toggle="collapse" data-target="#navbarResponsive" aria-controls="navbarResponsive" aria-expanded="false" aria-label="Toggle navigation">
                <span class="navbar-toggler-icon"></span>
            </button>
            <div class="collapse navbar-collapse" id="navbarResponsive">
                <ul class="navbar-nav ml-auto">
                    <li class="nav-item">
                        <a class="nav-link" href="#">About</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="upcoming-auctions.php">Upcoming Auctions</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="#">Contact</a>
                    </li>
                    <li class="nav-item dropdown">
                        <a class="nav-link dropdown-toggle" href="#" id="navbarDropdownBlog" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
                            Username
                        </a>
                        <div class="dropdown-menu dropdown-menu-right" aria-labelledby="navbarDropdownBlog">
                            <a class="dropdown-item" href="#">Profile</a>
                            <a class="dropdown-item" href="dashboard.php">Dashboard</a>
                            <a class="dropdown-item" href="logout.php">Logout</a>
                        </div>
                    </li>
                </ul>
            </div>
        </div>
    </nav>
<?php
}else{
    ?>
    <!-- Navigation -->
    <nav class="navbar fixed-top navbar-expand-lg navbar-dark bg-dark fixed-top">
        <div class="container">
            <a class="navbar-brand" href="index.php">E-Auction</a>
            <button class="navbar-toggler navbar-toggler-right" type="button" data-toggle="collapse" data-target="#navbarResponsive" aria-controls="navbarResponsive" aria-expanded="false" aria-label="Toggle navigation">
                <span class="navbar-toggler-icon"></span>
            </button>
            <div class="collapse navbar-collapse" id="navbarResponsive">
                <ul class="navbar-nav ml-auto">
                    <li class="nav-item">
                        <a class="nav-link" href="#">About</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="upcoming-auctions.php">Upcoming Auctions</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="#">Contact</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="login.php">Login</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="reg.php">Signup</a>
                    </li>
                </ul>
            </div>
        </div>
    </nav>
<?php
}
?>