php achieve calculator functions

//计算器
class jisuanqi{
	public $num1; //定义两个操作数
	public $num2;
	public function __construct($num1,$num2){  //创建构造函数初始化成员属性  
		$this->num1=$num1;
		$this->num2=$num2;
	
	}
	public function add(){ //加法运算
		return ($this->num1)+($this->num2);
	
	}
	public function jian(){ //减法运算
		return ($this->num1)-($this->num2);
	
	}
	public function cheng(){ //乘法运算
		return ($this->num1)*($this->num2);
	
	}
	public function chu(){  //除法运算
		if($this->num2==0){  //设置条件判断使除数不为零
			echo "除数不能为零";
		
		}else{
		return ($this->num1)/($this->num2);}
	
	}

}
$num1=40;  //为操作数赋值
$num2=20;
$j1=new jisuanqi($num1,$num2); //实例化类!
echo $num1."+".$num2."=".$j1->add();
echo "<br>";
echo $num1."-".$num2."=".$j1->jian();
echo "<br>";
echo $num1."*".$num2."=".$j1->cheng();
echo "<br>";
echo $num1."/".$num2."=".$j1->chu();

Results are as follows:
40 + 20 = 60
40-20 20 =
40 20 = 800 *
40/20 = 2