main.cpp

#include <iostream>
using namespace std;

class Shape {
  protected: double areaValue;
  public:
        virtual void area() = 0;
};

class Triangle: public Shape {
  protected: int height, base;
  public: 
          Triangle(int h, int b){
            height = h;
            base = b;
          }
          void area(){
            areaValue = 0.5*base*height;
            cout<<"Calculating Triangle area."<<endl<<"Area = "<<areaValue<<" sq. units"<<endl<<endl;
          }
};

class Rectangle: public Shape {
  protected: int length, breadth;
  public: 
          Rectangle(int l, int b){
            length = l;
            breadth = b;
          }
          void area(){
            areaValue = length*breadth;
            cout<<"Calculating Rectangle area."<<endl<<"Area = "<<areaValue<<" sq. units"<<endl<<endl;
          }
};

class Circle: public Shape {
  protected: int radius;
  public: 
          Circle(int r){
            radius = r;
          }
          void area(){
            areaValue = 3.14*radius*radius;
            cout<<"Calculating Circle area."<<endl<<"Area = "<<areaValue<<" sq. units"<<endl<<endl;
          }
};

int main() {
  Shape *ptr;
  Triangle ob1(4,3);
  Rectangle ob2(3,6);
  Circle ob3(5);

  ptr = &ob1;
  ptr->area();

  ptr = &ob2;
  ptr->area();

  ptr = &ob3;
  ptr->area();

}