I am using CodeIgniter ..I can't access the method from the controller

I have this script in my view

```
<script>
  function showHint(str){
    if (str.length==0){ 
        document.getElementById("txtHint").innerHTML="";
        return;
    }
    var xmlhttp=new XMLHttpRequest();
    xmlhttp.onreadystatechange=function(){
        if (xmlhttp.readyState==4 && xmlhttp.status==200){
               document.getElementById("txtHint").innerHTML=xmlhttp.responseText;
         }
    }
    xmlhttp.open("GET","ajax/ajaxSearch",true);
    xmlhttp.send();
  }
  </script>

```

and i have a controller named ajax with a method ajaxSearch()

```
public function ajaxSearch(){
    echo "received";
}

```

Folder Structure

```
htdocs/
     AjaxTry/
        AjaxSearchingMVC/
            application/
                controller/
                    ajax.php                //controller
                          ajaxSearch()      //method
                views/
                    view_ajax.php           // here is where the script is written

```

What could be the possible problem here?