如何'添加'和'减去'$变量到URL字符串？

Question

Having a problem here....

I can't seem to find a good way to 'add' and 'subtract' $variables to an URL string....

Here is my example:

in the url I have http://mywebsite.com/index.php?y=2011

For source code I have:

$currentPage = $_SERVER['PHP_SELF'];

Then if I want to add different $variables to the url string, I have been trying this...:

    echo '<a href="$currentPage.&t=col">College</a>';

But it isn't keeping the value of the current URL.. .?

It displays : http://mywebsite.com/index.php?&t=col

Instead of : http://mywebsite.com/index.php?y=2011&t=col (doesn't keep the $y variable)

I also need to find a way to change the $y and $t variable by any links, so I can easily change it to 2010, or 2009, with keeping the current $t variable.. ???

Thanks in advance!

HERE IS What I came up with from the great help!!!

$url = "http://www.mywebsite/index.php?";
foreach($_GET as $key=>$val){
$url.="$key=$val&"; }
echo '<a href="' . htmlspecialchars($url . 't=col') . '">College</a>';

Answer 1

As you may know, all variables passed through an URL are available in the $_GET array. Therefore, you can set up your link with something like this:

$url = "http://site.com/index.php?";
foreach($_GET as $key=>$val){
$url.="$key=$val&"; }

This gives you the benefit of also checking for certain variables and removing some that might be added by the user maliciously. And it also allows you to change your variables accordingly, as $key will contain either t or y