世界上有没有人知道为什么这个PHP对象调用不起作用？

I'm pretty new on PHP programming. I'm trying to do something not very difficult, nonetheless following VERY BASIC code does not either return an error or displaying any output. Playing around I guess it's related to $this->... line, I can't figure out why calling the function inside the object is not working. Please Help !!!

class TargetBuy {

    public $ClientCode;
    public $Service;
    public $ServiceType; // Emissione, Cambio, Riemissione, Rimborso, NoShow... 
    public $RateType; // tipo tariffa
    public $Segment; // tratta
    public $CityHotel;
    public $TicketType; // one way or round trip
    public $AdvancePurchase;
    public $Penalty;
    public $Taxes; // 0=NotIncluded; 1=Included
    public $FinalPrice;

    function CalculateTB_Price() {  
        $this->ClientCode='Hello';
        echo $ClientCode;
    }

}

$TB = new TargetBuy;

$TB->CalculateTB_Price();

because in the last row in the function, you print the var $ClientCode and not the var $this->ClientCode

$ClientCode is not defined, please enable proper error reporting which would have warned you about that. Instead, you have to use echo $this->ClientCode;.

You should read the basics about object oriented programming.