按照书上的写了个计算图形面积的程序，但是不执行计算，请问哪里出错了

《细说php》第8章的最后一个例子。可以创建表单，但是点击计算之后出错误。请各位大侠指点迷津
接口：class__Shape.php
interface Shape{
function area();
function perimeter();
}
?>
矩形：class__Rect.php
class Rect implements Shape{
private $width;
private $length;

function __construct($size=""){
$this->width=$size["width"];
$this->length=$size["length"];
}
function area(){
return $this->length * $this->width;
}
function perimeter(){
return 2 * ($this->width + $this->length);
}
}
?>
三角形：class__Triangle.php
class Triangle implements Shape{
private $length1;
private $length2;
private $length3;

function __construct($size=""){
$this->length1 = $size["length1"];
$this->length2 = $size["length2"];
$this->length3 = $size["length3"];
}
function area(){
$s = ($this->length1 + $this->length2 + $this->length3)/2;
return sqrt($s * ($s - $this->length1) * ($s - $this->length2) * ($s - $this->length3));
}
function perimeter(){
return $this->length1 + $this->length2 + $this->length3;
}
}
?>
圆形：class__Circle.php
class Circle implements Shape{
private $radius;

function __construce($size=""){
$this->radius = $size["radius"];
}
function area(){
return pi() * $this->radius * $this->radius;
}
function perimeter(){
return 2* pi() * $this->radius;
}
}
?>
表格：class__Form.php
class Form{
private $formName;
private $request;
private $action;
private $method;
private $target;

function __construct($formName,$request,$action="index.php",$method="get",$target="_self"){
$this->formName=$formName;
$this->request=$request;
$this->action=$action;
$this->method=$method;
$this->target=$target;
}
function __toString(){
$str="";
$str.="

".$this->formName."

";
$str.="

";

return $str;
}
}
?>
控制程序：index.php





function __autoload($className){
include ('class__'.ucfirst($className).'.php');
}
?>

图形周长和面积计算器

---

矩形||
三角形||
圆形


switch ($_REQUEST["action"]){
case 1:
$form=new Form("矩形",$_REQUEST,"index.php");
echo $form;
break;
case 2:
$form=new Form("三角形",$_REQUEST,"index.php");
echo $form;
break;
case 3:
$form=new Form("圆形",$_REQUEST,"index.php");
echo $form;
break;
default:
echo "请选择一个图形
";
}

if(isset($_REQUEST["act"])){
switch($_REQUEST["act"]){
case 1:
$shape=new Rect($_REQUEST);
break;
case 2:
$shape=new Triangle($_REQUEST);
break;
case 3:
$shape=new Circle($_REQUEST);
break;
}
echo "面积为：".$shape->area()."
";
echo "周长为：".$shape->perimeter()."
";
}
?>

回复讨论(解决方案)

没人看？都还没睡醒吗？

class__Form.php 中
$str.="";

return $str;
}
}
?>
index.php:





function __autoload($className){//包含到类时，自动加载到本页
include ("class__".ucfirst($className).".php");//自动加载相应的类所在的文件
}
?>

矩形||
三角形||
圆形

---

switch($_REQUEST["action"]){
case 1:
$form=new Form("矩形",$_REQUEST,"index.php");
echo $form;
break;
case 2:
$form=new Form("三角形",$_REQUEST,"index.php");
echo $form;
break;
case 3:
$form=new Form("圆形",$_REQUEST,"index.php");
echo $form;
break;
}

if(isset($_REQUEST["act"])){
switch ($_REQUEST["act"]){
case 1:
$shape=new Rect($_REQUEST);
break;
case 2:
$shape=new Triangle($_REQUEST);
break;
case 3:
$shape=new Circle($_REQUEST);
break;
}
echo "面积：".$shape->area()."
";
echo "周长：".$shape->perimeter()."
";
}
?>


其他的代码没有变，到底问题出在哪啊？？

class__Form.php

formName=$formName;$this->request=$request;$this->action=$action;$this->method=$method;$this->target=$target;}function __toString(){$str="";$str.="
".$this->formName."
";$str.="
";return $str;}}?>

index.php

图形周长和面积计算器
矩形||三角形||圆形
";}if(isset($_REQUEST["act"])){switch($_REQUEST["act"]){case 1:$shape=new Rect($_REQUEST);break;case 2:$shape=new Triangle($_REQUEST);break;case 3:$shape=new Circle($_REQUEST);break;}echo "面积为：".$shape->area()."
";echo "周长为：".$shape->perimeter()."
";}?>

我这个眼神啊！搞定。犯了超级低级的错误。