Am I not using the _GET function properly to open another page? - php

Question

I'm asking this because my teacher was displeased with how it worked. By that I mean ,when I typed in the query string to change sites, instead of typing ?page=flight and it staying that way it changed to../flight-details.php which is the direct page name.
Router.php:
<?php
$nav =array("home"=>"home.php",
"flight"=>"flight-detail.php",
"order"=>"order-flight.php",
"testimonial"=>"add-testimonial.php");
if ( isset ($_GET) )
{
header('Location: ' . $nav[$_GET['page']]);
}
else
{
header('Location:index.php');
}

Answer 1

There are few issues with your code, such as:
$_GET is a superglobal array, right now you are just checking whether the array is set or not. Your if condition should be like this:
if(isset($_GET['page']) && in_array($_GET['page'], array_keys($nav))){ ...
Otherwise you would get undefined index error if someone types anything other than the following four combinations, ?page=home&..., ?page=flight&..., ?page=order&... and ?page=testimonial&....
header(...); is not enough to redirect the user to a different page, use exit(); immediately after header(...); statement.
So your code should be like this:
$nav =array("home"=>"home.php",
"flight"=>"flight-detail.php",
"order"=>"order-flight.php",
"testimonial"=>"add-testimonial.php");
if(isset($_GET['page']) && in_array($_GET['page'], array_keys($nav))){
header('Location: ' . $nav[$_GET['page']]);
}else{
header('Location:index.php');
}
exit();
Here's the relevant reference:
http://php.net/manual/en/function.array-keys.php