215: Create a C++ program that uses single inheritance to model a simple shape hierarchy. Implement a base class "Shape" with a virtual function "printArea." Derive classes "Rectangle" and "Triangle" from "Shape" and override the "printArea" function to calculate and display their respective areas.

Virtual and Override:

1. Virtual: You use 'virtual' keyword with the function in the base class that is to be overridden in the derived class
2. Override: You use 'override' keyword with the function that is being overridden in the derived class.
3. This shows an error during compile-time when the names of virtual and override functions are not same.
4. Example:
   
   class base

   {

   public:

       virtual void print() { cout << "This is a base function\n"; }

   };

   
   

   class derived : public base

   {

   public:

       void print() override { cout << "This is an overridden function\n"; }

   };

Practice 1:

// Write a C++ program to demonstrate single inheritance by creating a base class "Circle" with a member

// function to calculate the area of circle and a derived class "new_Circle" to calculate the area of a circle

// if radius is positive and print a messege if radius is negative.

#include <iostream>

using namespace std;

class Circle

{

protected:

    float radius;

public:

    Circle(float rad = 0) { radius = rad; }

    virtual float calc_Area();

};

float Circle ::calc_Area() { return (3.14 * radius * radius); }

class new_Circle : public Circle

{

public:

    new_Circle(float rad = 0) { radius = rad; }

    float calc_Area() override;

};

float new_Circle ::calc_Area()

{

    if (radius < 0)

    {

        cout << "Radius should not be negative\n";

        return 0.0;

    }

    else

    {

        return (3.14 * radius * radius);

    }

}

int main()

{

    new_Circle c1(5.4);

    cout << "Area of circle: " << c1.calc_Area() << endl;

    return 0;

}