(this) pointer is added.
this pointer contains the address of the object through 
which function is called.
this->data member will give the data of the object.

"this" (i.e. Pointer to the object which call the member
function) is passed as the argument when a member function
is called.

Ex:

   class Employee{
        public:
          int member_Function1(){}
          void display()
          {
              do something;
          }
};
int main()
{
   Employee e1;
   e1.member_Functiuon(int a, int b);------> refer below 
1...
}

1...

Here e1 is an object of Employee Class.
Now e1.member_Function(int a, int b) means 
      implicitly the this pointer is applied to the 
function as

      member_Function(Employee *const this, int a, int b).

      Here the implicit this is a constant pointer to the 
object's address of type Employee. Once the Object has been 
created the address is given to it(e1). the address is 
passed as the first argument becoz the function resolving 
is faster...