添加如下几天语句页面变为空白，删除正常
echo "isset($tireqty)".isset($tireqty)."<br/>";
echo "isset($nothere)".isset($nothere)."<br/>";
echo "isset($tireqty)".empty($tireqty)."<br/>";
echo "isset($nothere)".empty($nothere)."<br/>";
下面列出完整代码
<html>
<head>
<title>Bob's Auto Parts -Order Result</title>
</head>
<body>
<h1>Bos's Auto Parts</h1>
<h2>Order Result</h2>
<?php
define('TIREPRICE',100);
define('OILPRICE',10);
define('SPARKPRICE',4);
$tireqty = $_POST['tireqty'];
$oilqty = $_POST['oilqty'];
$sparkqty = $_POST['sparkqty'];
echo " <p>Order processed at".date('H:i, jS F Y')."</p>";
echo " <p>Your order is as follow:</p>";
echo $tireqty." tireqty<br/>";
echo $oilqty." oilqty<br/>";
echo $sparkqty." spark plugs <br/>";
$totalqty = 0;
$totalqty = $tireqty + $oilqty + $sparkqty;
echo "Items ordered: ".$totalqty."<br/>";
$totalamount = 0.00;
$totalamount = $tireqty * TIREPRICE +
$oilqty * OILPRICE + $sparkqty * SPARKPRICE;
echo "Subtotal: $".number_format($totalamount,2)."<br/>";
$taxrate = 0.10; //total sales tax is 10%
$totalamount = $totalamount * (1 + $taxrate);
echo "Total including tax: $".number_format($totalamount,2)."<br/>"// echo "isset($tireqty)".isset($tireqty)."<br/>";
// echo "isset($nothere)".isset($nothere)."<br/>";
// echo "isset($tireqty)".empty($tireqty)."<br/>";
// echo "isset($nothere)".empty($nothere)."<br/>";
?>
</body></html>
前面的引号类的变量$nothere没有定义会报错，你没有开启debug模式就不会报错，也不会显示
isset和empty返回的都是bool类型，自然是不会显示的
error_reporting(E_ALL);
ini_set("display_errors", 1);
添加到页面顶端
echo "isset($tireqty)"...如果$tireqty没有定义会出错，因为这里双引号里面的isset是作为字符输出的