Change member of a class from another class

[Mxt]

Hi,

the friend declaration does only say that B has access to A's private and protected elements.

But an instance of B does not know in which instance of A it should change the value of state. You could have something like this

A a, b, c;

there are three objects of type A, which one do you want to change ?

One possible solution would be giving B's update a parameter

class B{
  public:
  void update(A& a){
    a.state = 1;
  }

};

and using it this way

void loop() {
  // put your main code here, to run repeatedly:
  first.update();
  second.update(first);
}

Much better C++ would be giving A a changeState method, instead of using friend.