navbar.php

    <nav class="navbar navbar-expand-lg navbar-dark bg-dark">
        <div class="container-fluid">
            <a class="navbar-brand" href="#">TeleDoc</a>
            <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#navbarNav"
                aria-controls="navbarNav" aria-expanded="false" aria-label="Toggle navigation">
                <span class="navbar-toggler-icon"></span>
            </button>
            <div class="collapse navbar-collapse" id="navbarNav">
                <ul class="navbar-nav ml-auto">
                    <li class="nav-item">
                        <a class="nav-link" href="index.php">Home</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="search.php">Search</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="about.php">About</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="contact.php">Contact</a>
                    </li>
                    <?php if(isset($_SESSION['username'])): ?>
                        <li class="nav-item">
                            <a class="nav-link" href="profile.php">Profile</a>
                        </li>
                        <li class="nav-item">
                            <a class="nav-link" href="logout.php">Logout (<?php echo $_SESSION['username']; ?>)</a>
                        </li>
                    <?php else: ?>
                        <li class="nav-item active">
                            <a class="nav-link" href="login.php">Login</a>
                        </li>
                        <li class="nav-item">
                            <a class="nav-link" href="register.php">Register</a>
                        </li>
                    <?php endif; ?>
                </ul>
            </div>
        </div>
    </nav>