html5 - php中添加了如下语句出现空白页删除页面zhengchang-PHP中文网问答

添加如下几天语句页面变为空白，删除正常
echo "isset($tireqty)".isset($tireqty)." ";
echo "isset($nothere)".isset($nothere)." ";
echo "isset($tireqty)".empty($tireqty)." ";
echo "isset($nothere)".empty($nothere)." ";

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)." ";
// echo "isset($nothere)".isset($nothere)." ";
// echo "isset($tireqty)".empty($tireqty)." ";
// echo "isset($nothere)".empty($nothere)." ";