Assign and modify php values across templates

Hi, I am trying to check for a php variable in each of my template in order to assign it a different styling but the value seems to disappear, can you please help, I already spent hours trying to figure this out. I know there is something small I’m missing.

So here is everything:

I have a page a which links to b and pass a value in the URI as https://www.b.com/?value=h

now the b file receive the value and change the global variable’s value to the one passed in the URI, then redirect back to the page.

This is the code in my b file:


$server = $_SERVER["REQUEST_URI"];
$valuePos = stripos($server, "=");

$nodes = substr($server, ($valuePos + 1));
$endPos = stripos($server, "e");
$gender = substr($server, ($valuePos + 1), ($endPos));

$valuePos = stripos($nodes, "-");

$redirecturl = substr($nodes, ($valuePos + 1));

header( 'Location: '.$redirecturl );

$gender is the global variable that I have declared in function.php, I have set its default value to neutral.

Now when I try to access $gender from another template it just displays the default value (neutral). Please help