#include <iostream>
#include <cmath>
using namespace std;

class Shape {
public:
    virtual double perimeter() const = 0;
    virtual double area() const = 0;
};

class Triangle: public Shape {
public:
    Triangle(double aa, double bb, double cc):a(aa), b(bb), c(cc) {}
    virtual double perimeter() const
    { return a + b + c; }
    virtual double area() const
    {   double p = (a + b + c)/2;
        return sqrt(p*(p-a)*(p-b)*(p-c));
    }
private:
    double a, b, c;
};

const double PI = 3.14;

class Circle: public Shape {
public:
    Circle(double rr):r(rr) {}
    virtual double perimeter() const
    { return 2*PI*r; }
    virtual double area() const
    { return PI*r*r; }
private:
    double r;
};

int main()
{
    //  Shape* s = new Shape;               // ERROR!!

    Shape* s = new Triangle(4, 5, 6);       // First s is a triangle
    cout << "Perimeter is " << s->perimeter() << endl;
    cout << "Area is " << s->area() << "\n";

    s = new Circle(10);                    // Now it is a circle
    cout << "Perimeter is " << s->perimeter() << endl;
    cout << "Area is " << s->area() << "\n";

    return 0;
 }

Пример: Потоковата библиотека на С++ се състои от няколко класове, свързани в следната йерархия:
 

#include<iostream>
using namespace std;

class Person  {
public:
    Person(string n) { name = n; }
    string get_name() const
    { return name; }
private:
    string name;
};

class Student : virtual
      public Person {
public:
    Student(string n):Person(n)
    {  id = "sid"; }
    virtual string get_id() const
    { return id; }
private:
    string id;
};

class Employee :  virtual
      public Person{
public:
    Employee(string n):Person(n)
    { id = "eid"; }
    virtual string get_id() const
    { return id; }
private:
    string id;
};

class TeachingAssistant : public Employee, public Student {
public:
    TeachingAssistant(string n): Employee(n), Student(n),
    Person(n)
    {}
//    string get_id() const;
    string student_id() const;
};

string TeachingAssistant::student_id() const
// Make student value available by a different name
{
    return Student::get_id();
}

int main()
{
    TeachingAssistant* fred = new TeachingAssistant("Fred");
    Employee* new_hire = fred; // Legal, because a TeachingAssistant is-a Employee
    Student* advisee = fred;  // Legal, because a TeachingAssistant is-a Student
    cout << "Your name is " << fred->get_name() << endl;
    
    Student* mary = new Student("Mary");
 //   Student* mary = new TeachingAssistant();
    TeachingAssistant* lab_instructor = dynamic_cast<TeachingAssistant*>(mary);
    
    if (lab_instructor != NULL)
        cout << "Yes, mary is a TeachingAssistant. \n";
    else
        cout << "No, mary is not a TeachingAssistant. \n";
    
    return 0;
}