Using a class inside of another class I have a seemingly simple problem that seems to be popular, but after searching several forums I still have not found the answer: How do you use a class inside of another class?

I have simplified my problem:

class A {
  const int pin;
  public:
  A(int attachPin) : pin(attachPin) {
  }

  void setup() {
    pinMode(pin, INPUT_PULLUP);
  }
};

class B {
  A myA;
  public:
  B(int a_attach) : myA(a_attach) {
  }

  void setup() {
    myA.setup();
  }
};

B test;

void setup() {
   test.setup();
}

void loop() {
}
I think, the problem in that line B test. You are define a variable, but you forget to define default constructor ( B() ). You try to setup an A class with unknown pin! To avoid this you may define test variable in that way B test(2); or in that way const int test_pin = 2; B test(test_pin);. Also to avoid this problem you may to set default value to the constructor sucha as  B(int attach=2) : myA(attach) {} and define test variable, as you do in your code B test;.