$navLinks = array(
    1 => array($locationHome, 'Home'),
    2 => array($locationSubscribe, '(Un)Subscribe'),
    3 => array($locationAbout, 'About'),
    4 => array($locationLogin, 'Login'),
);

if (!isset($navLinks[$nav_id])) {
    echo "An error occurred with loading the navigation";
    return;
}

foreach ($navLinks as $id => $linkInfo) {
?>
<a href="<?= $linkInfo[0] ?>" class="menu"><li class="<?= $id == $nav_id ? 'Selected' : 'Unselected' ?>"><?= $linkInfo[1] ?></li></a>
<?php
}