add virtual methods

add interface
add pure virtual
add casts
add template example

CPlusPlus/intro/ClassB.cpp

@@ -0,0 +1,12 @@
+#include "ClassB.h"
+
+ClassB::ClassB()
+{
+	std::cout << "ClassB called" << std::endl;
+	GetNumber();
+}
+
+ClassB::~ClassB()
+{
+	std::cout << "~ClassB called" << std::endl;
+}