Polymorphism and Virtual Functions Lab · Object Oriented Programming · Learn CSIT

Polymorphism and Virtual Functions Lab

CSC-166 · Semester II · Object Oriented Programming

intermediate30 minAvailable

C++in-browser interpreter · runs locally

#include <iostream>
using namespace std;

class Rectangle {
public:
  int w, h;
  int area() { return w * h; }
};

class Circle {
public:
  float r;
  float area() { return 3.14159 * r * r; }
};

int main() {
  Rectangle rect;
  rect.w = 4; rect.h = 5;
  Circle circ;
  circ.r = 2;
  cout << "Rectangle area = " << rect.area() << endl;
  cout << "Circle area = " << circ.area() << endl;
  return 0;
}

25 lines

Output

Write some code, then press Run. Stdout and errors appear here.

Lab brief

Objective

Demonstrate runtime polymorphism with virtual functions and an abstract base class.

Theory & concepts

Marking a base method virtual makes calls dispatch at runtime to the real object type. A pure virtual function (= 0) makes the base abstract: it cannot be instantiated, and every concrete derived class must implement it.

Rendering diagram…

Abstract Shape with concrete derived classes

class Shape {
  public:
    virtual double area() const = 0;
    virtual ~Shape() {}
};
class Circle : public Shape {
  public:
    double area() const override { return 3.14159 * r * r; }
};

Prerequisites

Lesson: Virtual functions and late binding
Lesson: Pure virtual functions and abstract classes

Instructions

1Define abstract class Shape with pure virtual area().
2Derive Circle, Rectangle and Triangle, each overriding area().
3Declare an array of Shape* pointing to each concrete object.
4Loop over the pointers and print every area.
5Remove the virtual keyword temporarily and observe the change in output.

Tasks

Three shapes
Implement area() correctly for Circle, Rectangle and Triangle.
Polymorphic loop
Print each area through a base pointer in one loop.
Observe binding
Explain why removing virtual changes which area() runs.

Self-check

The loop calls each derived area() correctly.
The student explains late binding and the vtable concept.
Removing virtual demonstrates static binding with base results.

Environment

editorstdout consolecompiler errorstest cases