php navigation using get or include - php

Question

index.php is controlling the site.
I have elseif include based on variable $p
right now $p does not have anything in it and i'm not understanding why.
Also is using include the industry standard or would GET be a better choice?
In the header file which is included on index.php but it just takes me to the page link instead of storing the page in $p
<?php
$pages = array(
"home" => "HOME",
"services" => "SERVICES",
"employees" => "EMPLOYEES",
"contact" => "CONTACT");
$p = (isset($_GET['p'])) ? $_GET['p'] : "";
foreach ($pages as $url => $label) {
echo '<li ';
if ($p == $url) { echo '<li><a class="active" href="' . htmlspecialchars(urlencode($url)). '.php">'
. htmlspecialchars($label) . '</a></li>'; } else { echo '<li>' . $label . '</li>'; }
}
?>
This is the index.php file:
<?php include('includes/header.php'); ?>
<?php
if ($p == "services") {
include("services.php");
} elseif($p == "employees") {
include("employees.php");
} elseif($p == "contact") {
include("contact.php");
} else {
include("home.php");
};
?>
<?php include('includes/footer.php'); ?>

Answer 1

It really depends on what you are trying to do. Maybe I am misunderstanding your question, however include and $_GET are two completely separate things.
$_GET is an array of the query string out of your URL. So, for instance, if your URL was mysite.com/index.php?a=rawr&p=services then $_GET would be array("a" => "rawr", "p" => "services"); If you don't have any parameters in your URL assigned to p, then $_GET["p"] would be empty
Source:
http://www.php.net/manual/en/reserved.variables.get.php
EDIT:
I think I'm starting to understand your question now. Using your current method would be fine, I would just change up the code slightly:
<?php
$pages = array(
"home" => "HOME",
"services" => "SERVICES",
"employees" => "EMPLOYEES",
"contact" => "CONTACT"
);
$p = (isset($_GET['p'])) ? $_GET['p'] : "";
foreach ($pages as $url => $label) {
?>
<li><a <?= $p == $url ? 'class="active"' : ""?> href="index.php?p=<?=$url?>" > <?=$label?> </a></li>
<?php
}
?>