关于代码分号结尾问题

<?php

$p = "";//定义圆周率的两种取值；

define("PI1",3.14);//定义变量PI变为常量3.14；

define("PI2",3.142);

$height = "中";//定义值得精度；

if($height == "中"){$p = "PI1";}

else if($height == "低"){$p = "PI2";}

$r = 1;

$area = constant($p)*$r*$r;

echo $area

?>

if($height == "中"){$p = "PI1";}     

else if($height == "低"){$p = "PI2";}

    为什么分号要再中括号里面打。而不是外面，不是以分号结尾吗