php数值转换进行数学运算,有点小问题啊
<?php
$height.="<script language=\"javascript\">";
$height.="document.write(document.body.clientHeight);";
$height.="</script>";
echo $height; //通过javascript获取网页可用分辨率,可以正常输出
echo "<br>";//下面我想把获取分辨率的值进行数学运算
$a=$height-100;
echo $a;// 输出-100
echo "<br>";
$b = (int) $height-100;
echo $b;//还是输出-100
//要怎么样才能运算啊
?>