Issue setting z-index and class via php - php

Question

I have a bit of php code that sets the z-index and class of different tabs options within my menu in a header file. The header file is included into every page, then this code will determine what tab is active so the z index and css can be changed. My problem is that this code, no matter what $url equals, gives the home tab a z-index of 1000 and a class of "active tab". It seems to me like I have everything right in my if statement, does anyone know why It wont detect say, documentation.php and apply the 1000 z-index to this?
<?php
$zi_home = "10";
$zi_ss = "10";
$zi_tes = "10";
$zi_order = "10";
$zi_con = "10";
$tab_home = "inactive-tab";
$tab_ss = "inactive-tab";
$tab_tes = "inactive-tab";
$tab_order = "inactive-tab";
$tab_con = "inactive-tab";
$url = $_SERVER['REQUEST_URI'];
if ($url = "/index.php") {
$zi_home = "1000";
$tab_home = "active-tab";
} elseif ($url = "/documentation.php") {
$zi_ss = "1000";
$tab_ss = "active-tab";
} elseif ($url = "/order.php") {
$zi_tes = "1000";
$tab_tes = "active-tab";
} elseif ($url = "/about.php") {
$zi_order = "1000";
$tab_order = "active-tab";
} elseif ($url = "/contactus.php") {
$zi_con = "1000";
$tab_con = "active-tab";
}
?>
header.php file snippet:
<div class="<? echo $tab_home; ?>" style="z-index: <? echo $zi_home; ?>;">
Home
</div>
<div class="<? echo $tab_ss; ?>" style="z-index: <? echo $zi_ss; ?>;">
Documentation
</div>

Answer 1

You used = instead of ==. If you change those out it looks like it will work. Should be:
if ($url == "/index.php") {
$zi_home = "1000";
$tab_home = "active-tab";
} elseif ($url == "/documentation.php") {
$zi_ss = "1000";
$tab_ss = "active-tab";
} elseif ($url == "/order.php") {
$zi_tes = "1000";
$tab_tes = "active-tab";
} elseif ($url == "/about.php") {
$zi_order = "1000";
$tab_order = "active-tab";
} elseif ($url == "/contactus.php") {
$zi_con = "1000";
$tab_con = "active-tab";
}