add pure virtual

add interfaces like classes
add template example

CPlusPlus/intro/ClassA.h

@@ -1,6 +1,7 @@
 #pragma once
+#include "IComparable.h"
 
-class ClassA
+class ClassA : public IComparable
 {
 	// private
 
@@ -8,7 +9,10 @@ public:
 	// public
 	ClassA(); // default constructor
 	ClassA(const ClassA& other); // copy constructor
-	~ClassA(); // destructor
+	virtual ~ClassA(); // destructor
+
+	const int& GetNumber() const { return *_pNumber; } // implicit inline method
+	bool Compare(IComparable* pOther) override;
 
 protected:
 	// protected