diff --git a/CPlusPlus/intro/ClassA.cpp b/CPlusPlus/intro/ClassA.cpp
index 72f3932..05e2bc4 100644
--- a/CPlusPlus/intro/ClassA.cpp
+++ b/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()
+{
+}
diff --git a/CPlusPlus/intro/ClassA.h b/CPlusPlus/intro/ClassA.h
index ca6753a..c7fd632 100644
--- a/CPlusPlus/intro/ClassA.h
+++ b/CPlusPlus/intro/ClassA.h
@@ -1,6 +1,7 @@
 #pragma once
+#include "IPrintable.h"
 
-class ClassA
+class ClassA : public IPrintable
 {
 	// private
 
@@ -10,6 +11,9 @@ public:
 	ClassA(const ClassA& other); // copy constructor
 	~ClassA(); // destructor
 
+	const int& GetNumber() const { return *_pNumber; } // implicit inline method
+	void Print() override;
+
 protected:
 	// protected
 
diff --git a/CPlusPlus/intro/ClassB.cpp b/CPlusPlus/intro/ClassB.cpp
new file mode 100644
index 0000000..518d571
--- /dev/null
+++ b/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;
+}
diff --git a/CPlusPlus/intro/ClassB.h b/CPlusPlus/intro/ClassB.h
new file mode 100644
index 0000000..23cfcb2
--- /dev/null
+++ b/CPlusPlus/intro/ClassB.h
@@ -0,0 +1,10 @@
+#pragma once
+#include "ClassA.h"
+
+class ClassB : public ClassA
+{
+public:
+	ClassB();
+	~ClassB();
+};
+
diff --git a/CPlusPlus/intro/IPrintable.h b/CPlusPlus/intro/IPrintable.h
new file mode 100644
index 0000000..ce78377
--- /dev/null
+++ b/CPlusPlus/intro/IPrintable.h
@@ -0,0 +1,10 @@
+#pragma once
+#include <iostream>
+
+class IPrintable
+{
+public:
+	IPrintable() { std::cout << "IPrintable called" << std::endl; }
+	virtual ~IPrintable() { std::cout << "~IPrintable called" << std::endl; }
+	virtual void Print() = 0; // pure virtual
+};
\ No newline at end of file
diff --git a/CPlusPlus/intro/functions.h b/CPlusPlus/intro/functions.h
index 4751ff8..2fc66ae 100644
--- a/CPlusPlus/intro/functions.h
+++ b/CPlusPlus/intro/functions.h
@@ -10,4 +10,14 @@ void changeInt(int n);
 void changeIntPointer(int* pN);
 void changeIntReference(int& n);
 
+template<class T>
+void safeDelete(T*& pObj)
+{
+	if (pObj != nullptr)
+	{
+		delete pObj;
+		pObj = nullptr;
+	}
+}
+
 #endif // !__FUNCTIONS_H__
diff --git a/CPlusPlus/intro/intro.vcxproj b/CPlusPlus/intro/intro.vcxproj
index 1a0f083..4a50f2c 100644
--- a/CPlusPlus/intro/intro.vcxproj
+++ b/CPlusPlus/intro/intro.vcxproj
@@ -128,12 +128,15 @@
   </ItemDefinitionGroup>
   <ItemGroup>
     <ClCompile Include="ClassA.cpp" />
+    <ClCompile Include="ClassB.cpp" />
     <ClCompile Include="functions.cpp" />
     <ClCompile Include="main.cpp" />
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="ClassA.h" />
+    <ClInclude Include="ClassB.h" />
     <ClInclude Include="functions.h" />
+    <ClInclude Include="IPrintable.h" />
   </ItemGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
   <ImportGroup Label="ExtensionTargets">
diff --git a/CPlusPlus/intro/intro.vcxproj.filters b/CPlusPlus/intro/intro.vcxproj.filters
index c69c230..d3bb0c5 100644
--- a/CPlusPlus/intro/intro.vcxproj.filters
+++ b/CPlusPlus/intro/intro.vcxproj.filters
@@ -24,6 +24,9 @@
     <ClCompile Include="ClassA.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="ClassB.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
   </ItemGroup>
   <ItemGroup>
     <ClInclude Include="functions.h">
@@ -32,5 +35,11 @@
     <ClInclude Include="ClassA.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="ClassB.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
+    <ClInclude Include="IPrintable.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
   </ItemGroup>
 </Project>
\ No newline at end of file
diff --git a/CPlusPlus/intro/main.cpp b/CPlusPlus/intro/main.cpp
index ae854a8..109770c 100644
--- a/CPlusPlus/intro/main.cpp
+++ b/CPlusPlus/intro/main.cpp
@@ -3,6 +3,7 @@
 #include <memory>
 #include "functions.h"
 #include "ClassA.h"
+#include "ClassB.h"
 
 using namespace std;
 
@@ -107,8 +108,37 @@ int main()
 	//}
 	//cout << "sn2 refs: " << sn2.use_count() << endl;
 
-	ClassA classA;
-	ClassA classA2 = classA;
+	//ClassA classA;
+	//ClassA classA2 = classA;
+	//ClassB classB;
+	//int n = classA.GetNumber();
+	//cout << n << endl;
+	//classB.GetNumber();
+
+	IPrintable* pPrintable = nullptr;
+	pPrintable = new ClassB();
+	//(*pPrintable).Print();
+	//pPrintable->Print(); // same line as above, but simpler
+	////ClassB* pClassB2 = (ClassB*)pPrintable; // C-Cast, CAUTION: DANGER!!!
+	//ClassB* pClassB2 = dynamic_cast<ClassB*>(pPrintable); // c++ cast for polymorhpic cast
+	//float f = 1.0f;
+	//int i = static_cast<int>(f); // c++ cast, convert one static data type into another
+	////int* nonsense = reinterpret_cast<int*>(pPrintable); // c++ cast like C-Cast, CAUTION: DANGER!!!
+	//const char csz[13] = "Hello World";
+	//char* sz = const_cast<char*>(csz);
+
+	// What's the difference?
+	//const int* cip;
+	//int const* icp;
+	//int* const ipc;
+	//const int const* cicp;
+	//const int* const cipc;
+	//int const* const icpc;
+	//const int const* const cicpc;
+
+	//delete pPrintable;
+	//pPrintable = nullptr;
+	safeDelete(pPrintable);
 
 	return 0;
 }