php不分大小寫字串比對語法,檢査兩個字串是否相同

$comparison = strcasecmp($reply,$topic['answer']);//不分大小寫字串比對

 if($comparison==0){//相同則回傳0
  
  $img_change = 'pic_'.$id_now.'_light.png';//欲更新的圖片名稱組合
  $rs_img_change = $mysqli->prepare(" UPDATE `topic` SET `img`=?,`status`=1 WHERE id = ? ");
     $rs_img_change->bind_param('si', $img_change,$id_now);
     $rs_img_change->execute();

  echo "correct";
 }else{
  echo "error";
 }