php: getting a cookie value and adding by one - php

Question

<?php
$cwd = getcwd();
$dir = 'onlytest';
// get file names from logos directory
$files = scandir($dir);
// count total files in directory
$totalFiles = count($files) - 1;
// loop through file names and output the images
$desc = $files;
echo 'Hello '.($_COOKIE['number']!='' ? $_COOKIE['number'] : '2'); // number of cookie!
for ($i = (10 * $_COOKIE['number']) - 18; $i <= 10 * $_COOKIE['number']; $i++)
{
$text = substr($desc[$i],0,20).'...';
$filepath = $dir . "/" . $files[$i];
echo '<img src="' . $filepath . '" target="_blank" width="25%" height="33%" />';
echo "<a href='$filepath' target='_blank'>$text</a>";
}
echo "</br>";
?>
<script type="text/javascript" src="jquery.min.js"></script>
<script type="text/javascript">
function doSomething()
{
$.get("opentext.php");
return false;
}
</script>
'next 20 pictures'
My other file opentext.php is like this!
<?php
$number = ($_COOKIE['number'] + 1);
setcookie('number',$number,time() + (86400 * 1)); // 86400 = 1 day cookie
?>
I'm trying to take the value of cookie and add + 1, as you can see i want to take the 20 first pictures in folder and then i want to change the cookie when clicking the link below using javascript onclick function, it redirects me to the php file that adds + 1 to the cookie and gives the next 20 pictures, i have been doing this for hours and i just can't seem to get myself to find a solution.