[php] post ajax data to PHP and return data

How can i post some ajax data to the controller function and get it back? For I want to post one integer to the function, and get another integer (total votes for the item which ID is posted), and on success i want to echo that vote count. I dont know how can i post the "id" to the controller function. Please see my code:

//post this integet
the_id = $(this).attr('id'); 

        $.ajax({
            type: "POST",
            data: the_id,
            url: "http://localhost/test/index.php/data/count_votes",
            success: function(){
                //the controller function count_votes returns an integer.
                //echo that with the fade in here.

                }
            });

So what does count_votes look like? Is it a script? Anything that you want to get back from an ajax call can be retrieved using a simple echo (of course you could use JSON or xml, but for this simple example you would just need to output something in count_votes.php like:

$id = $_POST['id'];

function getVotes($id){
    // call your database here
    $query = ("SELECT votes FROM poll WHERE ID = $id");
    $result = @mysql_query($query);
    $row = mysql_fetch_row($result);

    return $row->votes;
}
$votes = getVotes($id);
echo $votes;

This is just pseudocode, but should give you the idea. What ever you echo from count_votes will be what is returned to "data" in your ajax call.

For the JS, try

data: {id: the_id}
...
success: function(data) {
        alert('the server returned ' + data;
    }

and

$the_id = intval($_POST['id']);

in PHP