Dynamisk bind-param Php

	$headline = $_GET['hl'];
	$county = $_GET['ca'];
	$categories = '$_GET['co']';
	
	$query = 'SELECT COUNT(id) FROM main_table';		
							
	$queryCond = array(); 
	$stringtype = array();
	$variable = array();
	
	
if (!empty($headline)) {
    $queryCond[] = "headline LIKE CONCAT ('%', ? , '%')";
   array_push($stringtype, 's');
   array_push($variable, $headline);
}

if (!empty($county)) {
    $queryCond[] = "county_id = ?";
    array_push($stringtype, 'i');
    array_push($variable, $county);
}

 if (!empty($categories)) {
    $queryCond[] = "categories_id = ?";
    array_push($stringtype, 'i');
    array_push($variable, $categories);
}

if (count($queryCond)) {
	
    $query .= ' WHERE ' . implode(' AND ', $queryCond);
}

//var_dump($query);

$stmt = $mysqli->prepare($query);

$variable = array_merge($stringtype, $variable);

//var_dump($params);


$refs = array();

//var_dump($refs);

foreach($variable as $key => $value)

	$refs[$key] = &$variable[$key];
  
call_user_func_array(array($stmt, "bind_param"), 	$refs);