index() function with parametrs

[eluser]mardon[/eluser]
Hi,

i have default controller site with index() function

Code:

function index($category){
$segs = $this->uri->segment_array();

  foreach ($segs as $segment)
  {
   echo $segment;
   echo '<br />';
  }
}

if i use localhost/site/2 i obtain error 404
localhost/site/index/2 is correct

but without parametr localhost/site is function ok

why the localhost/site/2 is not function?