Funciones Virtual Visual C++

#include <iostream>
#include <cstdlib>

using namespace std;

class Student
{
public:

 virtual void calTuition()
 {
  cout << "Se encuentra en Student :: calTuition()" << endl;
 }
};

class GraduateStudent : public Student
{
public:

 void calTuition()
 {
  cout << "Se encuentra en Student :: calTuition()" << endl;
 }
};

void fn( Student &x )
{
 x.calTuition();
}

int main( int argc , char *argv[] )
{
 Student s;
 fn( s );

 GraduateStudent gs;
 fn( gs );

 system("pause");
 return 0;
}