class in php

using class in php
<?php

class sinhvien{

var $toan,$ly,$hoa;

function __construct($toan,$ly,$hoa)

{

$this->toan=$toan;

$this->ly=$ly;

$this->hoa=$hoa;



}

var $tb;

function tinhdiem(){

$toan=$this->toan;

$ly=$this->ly;

$hoa=$this->hoa;

$this->tb=($toan+$ly+$hoa)/3;

echo "sinh vien co tong diem".$this->tb;

}

function xeploai()

{

$xl=$this->tb;

if($xl<5){ echo " trung binh" ;}

else if ($xl>5 &&$xl<7 ){echo " trung binh kha ";}

else echo"gioi";

}

}

$a=new sinhvien(4,7,15);

$a->tinhdiem();

$a->xeploai();



?>