php foundation knowledge！

 1 <?php
 2 $p = "PII";
 3 define("XPI",3.1415926);
 4 define("PI",3.14,true);
 5 define($p,3.14,false);
 6 echo XPI;
 7 echo "<br />xPI 默认false ：对大小写敏感！<br />";
 8 echo xPI;//默认false 对大小写敏感
 9 echo "<br />";
10 echo PI;
11 echo "<br />Pi 设置true ：对大小写不敏感！<br />";
12 echo Pi;
13 echo "<br />";
14 echo PII;
15 echo "<br />";
16 echo Pii;
17 echo "<br />";
18 ?>