Student Exercises
Questions such as these have appeared on previous exams.
They are good exercises in understanding inheritance,
virtual functions and polymorphism.
Exercise 1
Predict the output from this code. There are no compiler errors.
Cut and paste this code, then compile and link to verify
your predictions.
<![CDATA[
#include <iostream>
using namespace std;
class B
{
public:
virtual void Hello( ) const
{cout << "Hello from B\n"; }
virtual void IAm ( ) const
{ cout << "I am B\n"; }
void GoodBye( ) const
{ cout << "Bye from B\n"; }
};
class D : public B
{
public:
virtual void Hello ( ) const
{ cout << "Hello from D\n"; }
virtual void IAm ( ) const
{ cout << "I am D\n"; }
void GoodBye ( ) const
{ cout << "Bye from D\n"; }
};
class C : public D
{
public:
virtual void IAm ( ) const
{ cout << "I am C\n"; }
void GoodBye( ) const
{ cout << "Bye from C\n"; }
};
int main ( )
{
B *pB = new C;
pB->Hello( );
pB->IAm ( );
pB->GoodBye ( );
cout << endl;
D *pD = new C;
pD->Hello( );
pD->IAm ( );
pD->GoodBye ( );
cout << endl;
C *pC = new C;
pC->Hello( );
pC->IAm( );
pC->GoodBye( );
}
]]>
Exercise 2
For each pair of lines of code in main( ), determine
whether or not the code creates a compiler error.
If so, state why. If not, what is output by the code.
You can verify your answers by copying/pasting this
code and then compiling/linking and running it.
When you see a compiler error, comment out that code
to continue.
<![CDATA[
#include <iostream>
using namespace std;
class A
{
protected:
int val;
public:
virtual void Foo( )
{ cout << "A in Foo!" << endl; }
void Bar( )
{ cout << "A in Bar!" << endl; }
};
class B : public A
{
public:
void Bar( )
{ cout << "B in Bar!" << endl; }
};
class C : public B
{
public:
virtual void Foo( )
{ cout << "C in Foo!" << endl; }
void Bar( )
{ cout << "C in Bar!" << endl; }
};
class D : public A
{
public:
virtual void Foo( )
{ cout << "D in Foo!" << endl; }
};
void test( B* b)
{
b->Foo();
}
int main ( )
{
A *a1 = new B;
test( a1 );
C *c1 = new C;
test( c1 );
A a2;
a2.Foo();
B *b1 = new A;
b1->foo();
D d1;
test( &d1 );
A *a3 = new C;
a3->Bar();
B b2;
cout << b2.val;
return 0;
}
]]>
Last Modified: Monday, 28-Aug-2006 10:16:04 EDT