add virtual methods

add interface
add pure virtual
add casts
add template example

CPlusPlus/intro/ClassA.cpp

@@ -2,6 +2,7 @@
 
 ClassA::ClassA() : _pNumber(new int(0))
 {
+	std::cout << "ClassA called" << std::endl;
 }
 
 ClassA::ClassA(const ClassA& other)
@@ -15,9 +16,14 @@ ClassA::ClassA(const ClassA& other)
 
 ClassA::~ClassA()
 {
+	std::cout << "~ClassA called" << std::endl; 
 	if (_pNumber != nullptr)
 	{
 		delete _pNumber;
 		_pNumber = nullptr;
 	}
 }
+
+void ClassA::Print()
+{
+}