PHP Create and delete cookies using query strings
<a href="index.php?showDesktop=true">Show Desktop</a>

<a href="index.php?showMobile=true">Show Mobile</a>

if($_GET['showDesktop']) {
    $_COOKIE('showDesktop', 'yes');
    $_COOKIE('showMobile', null);
}
else if($_GET['showMobile']) {
    $_COOKIE('showDesktop', null);
    $_COOKIE('showMobile', 'yes');
}

setcookie('showDesktop', 'yes', time()+86400*365);
setcookie('showMobile', false);

setcookie('displayMode', 'desktop', time()+86400*365);

if($_GET['showDesktop'] == 'true') {
    setcookie('showDesktop', true);
    setcookie('showMobile', false);
}
else if($_GET['showMobile'] == 'true') {
    setcookie('showDesktop', false);
    setcookie('showMobile', true);
}

if($_GET['showDesktop']) {
    $_COOKIE('showDesktop', 'yes');
}
else if($_GET['showMobile']) {
    $_COOKIE('showDesktop', 'no');
}

setcookie ("showDesktop", "", time() - 3600);