abstract class Oper {
    public $num1 = 0;
    public $num2 = 0;

    abstract public function getResult();

}

class Add extends Oper {

    public function getResult(){
        $result = $this->num1 +$this->num2;
        return $result;
    }
}

class Div extends Oper {

    public function getResult(){
        if($this->num2==0){
            throw_exception(‘分母不能为零‘);
        }
        $result = $this->num1 /$this->num2;
        return $result;
    }

}

class Operate {

    public function oper($operate){
        switch ($operate){
            case ‘+‘:
                return new Add();
                break;
            case ‘-‘:
                return new Sub();
                break;
            case ‘*‘:
                return new Mul();
                break;
            case ‘/‘:
                return new Div();
                break;
            default:
                throw_exception(‘符号不支持‘);
                break;
        }
    }
}