how to concat query conditions using if statements

[eluser]mddd[/eluser]

Code:

$this->db->where('price', 50);
$this->db->where('type', 5);

if ($checked1==1)
{
   $cats = array();
   if ($checked2==2)
   {
      $cats[]=5;
      if ($checked3==3) $cats[]=10;
      $this->db->where_in('cat', $cats);
   }
}

$this->db->get('author');