<?php
$p"";
//定义圆周率的两种取值
define("PI1,3.14");
define("PI2,3.142");
//定义值的精度
$height = "中";
//根据常量返回常量名，将常量变成了一个可变的常量
if($heighe == "中")｛
$p = "PI1";
}else if($height == "低")｛
$p = "PI2";
}
$r=1;
“$area= constant($p)*$r*$r;”
echo $area;
?>
