add forward declaration examples

add class & inheritance examples

CPlusPlus/Classes/Monster.h

@@ -0,0 +1,16 @@
+#pragma once
+#include "Entity.h"
+#include "ICompareable.h"
+
+class Monster : public Entity, public ICompareable
+{
+public:
+	Monster(int strength);
+
+	virtual void Move() = 0; // abstract (pure virtual method)
+	std::string ToString() override;
+	int Compare(ICompareable* other) override;
+
+protected:
+	int _strength = 0;
+};