Question

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.

                }
            });

Answer 1

 $.ajax({
            type: "POST",
            data: {data:the_id},
            url: "http://localhost/test/index.php/data/count_votes",
            success: function(data){
               //data will contain the vote count echoed by the controller i.e.  
                 "yourVoteCount"
              //then append the result where ever you want like
              $("span#votes_number").html(data); //data will be containing the vote count which you have echoed from the controller

                }
            });

in the controller

$data = $_POST['data'];  //$data will contain the_id
//do some processing
echo "yourVoteCount";

Clarification

i think you are confusing

{data:the_id}

with

success:function(data){

both the data are different for your own clarity sake you can modify it as

success:function(vote_count){
$(span#someId).html(vote_count);