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";
}