我以前使用过这个代码一百万次，但现在我遇到了问题。
在我的 top.php 文件中，我将代码作为http://www.sentuamsg.com/index.php?action=about
现在，当我到达我的索引页面时，我收到错误代码通知：未定义变量：第 4 行 /home/content/90/9753290/html/index.php 中的操作
<?php
include("top.php");
if($action == "") {
echo "<p align=center><img src=mondaymoan.jpg></img></p>";
echo "<p><font face=Tahoma><b><font size=2>Monday Moan:</font></b> <font size=2>
All the weeks Gaming Action, Rumours, News snipplets assessed and talked about
all in one blog. Have a read of your own on this Monday's Moan</font></font></p>";
echo "<p align=right><font face=Tahoma size=2>[Read]</font></p>";
echo "<p><img src=mostloved.jpg></p>";
echo "<p align=center><img src=retrogamer.jpg></img></p>";
echo "<p><font face=Tahoma><b><font size=2>Retro Gamer:</font></b> <font size=2>
Taking on the games from the past, these games range from Video Game consoles to PC Games. One of our most popular feature as you the gamers relive the past with us through the joys and frustrations.</font></font></p>";
echo "<p align=right><font face=Tahoma size=2>[View]</font></p>";
include("bottom.php");
exit;
}
if($action == "action") {
echo "done";
include("bottom.php");
exit;
}
?>
为什么会发生此错误？我是否遗漏了某些东西，或者我是否使用了 php5 中未使用的非常古老的编码技术？