if i have a line such as:

HTML Code:
http://www.site.net/index.php?s=1
in my browser and i want to be able to click on another link in my website and end up with:

HTML Code:
http://www.site.net/index.php?s=1&t=2
what is the correct method to do this via an anchor tag?

i tried:

PHP Code:
<?php echo $PHP_SELF;?>?t=<?php echo $tnum;?>">
but as you will know that only returned:

HTML Code:
http://www.site.net/index.php?t=2
so what is the correct way? (without using cookies if possible)

many thanks for your help,