■Circle02.php
---
<?php
define("PI", 3.14);
function circle_area($r) {
	$area = $r * $r * PI;
	return $area;
}
?>
---

■Circle03.php
---
<?php
require_once "Circle02.php";
?>
<?php
$r = 10;
echo "半径 $r の円の面積は " . circle_area($r);
echo "<br>";
$r = 20;
echo "半径 $r の円の面積は " . circle_area($r);
echo "<br>";
?>
---