面向对象上

class Ren{
      public $code;  //成员变量
      public $name;   //姓名
      public $sex;   //性别
      public $birthday;   //生日
}   //需要哪些特征就放哪些特征，没必要全都仍在类里面

public  //公有的,在任何地方都可以访问到
protected  //受保护的
private  //私有的

$r = new Ren();
$r->code = "p001";
$r->name = "张三"

求一个圆的阴影面积
class Yuan{
    public $r;
    public function  mianji(){
           return 3.14*$this->r*$this->r
     }
}

$y1 = new Yuan();
$y1->r = 10;

$y2 = new Yuan();
$y2->r = 5;

$mjm = $y1->mianji()-$y2->mianji();
echo $mjm;

$r1 = 10;
$r2 = 5;
$mj = 3.14*$r1*$r1-3.14*$r2*$r2