Setcookie > sniff > output on same page

Answer 1

Simply check $_GET for the first time:

if(isset($_GET['key'])) { $cookievalue = $_GET['key']; }
if(isset($_COOKIE['cookname'])) { $cookievalue = $_COOKIE['cookname']; }

switch ($cookievalue) { case hmm01: echo "abc"; break; case hmm02: echo "def"; break; case hmm03: echo "ghi"; break; default: echo "hello"; } ?>

Answer 2

if (specific key/value in query string) $_COOKIE['cookname'] = "some value";

And learn some HTTP