我正在計算smarty中的總金額。我的HTML代碼如下:在smarty中實施數學運算
{foreach name = feach item = k from = $res}
<p>
Date : {$k->booking_date}<br />
Price : {$k->price}
{* $prc=$k->price, $seats=$k->number_of_seats *}
Balance :{math equation="x * y" x=$prc y=$seats} <br />
<span id="paid{$k->booking_id}">
<input type="button" onclick="makePaid('{$k->booking_id}')" value="PAID" />
</span>
</p>
{/foreach}
但它顯示警告消息說Warning: Smarty error: math: parameter x is empty in C:\..
。我在哪裏做錯了?