Quick and easy observer+decorator design pattern example base around printing a clock

Decorated-Observer.h

class ISubject;

class IObserver
{
protected:
	ISubject* m_Subject;

public:
	IObserver(ISubject* sub) : m_Subject(sub) {}

	virtual void Update() = 0;
};

class ISubject
{
private:
	std::vector<IObserver*> m_Observers;

public:
	ISubject() : m_Observers() {}

	void RegistarObserver(IObserver* obv) { m_Observers.emplace_back(obv); }
	virtual void Notify() { for each(IObserver* obv in m_Observers) { if (obv == nullptr) continue; obv->Update(); } }
};

class Clock : public ISubject
{
public:
  void Tick() { /*time++*/ Notify(); }
  
  int GetSec();
  int GetMin();
  int GetHr();
};

class ClockWatcher : public IObserver
{
public:
   virtual void Update() { std::cout << m_Subject.GetSec(); }
   
  int GetSec();
  int GetMin();
  int GetHr();
};

class ClockWatcherDecorator abstract : public ClockWatcher
{
  protected:
  ClockWatcher* m_Clock;
  
  public:
	ClockWatcherDecorator(ClockWatcher* sub) : m_Clock(sub) {}

	virtual void Update() = 0;
};

class MinuteWatcher : public ClockWatcherDecorator
{
   virtual void Update() { std::cout << m_Subject.GetMin(); m_Clock.Update(); }
}

class HourWatcher : public ClockWatcherDecorator
{
   virtual void Update() { std::cout << m_Subject.GetHr(); m_Clock.Update(); }
}
  

Main.cpp

#include "Decorated-Observer.h"

int main()
{
   Clock clock;
  
  HourWatcher watch(&MinuteWatcher(&ClockWater(&clock)));
   
  clock.RegistarObserver(&watch);
   
  for(int i = 0; i < 10; i += 1)
    clock.Tick();
  
  return 0;
}