Inheritance and polymorphism are two important concepts of object-oriented programming in C++. Inheritance allows a new class to acquire the properties and functions of an existing class, while polymorphism allows the same function call to behave differently depending on the object that invokes it. These concepts make programs more organized, reusable, flexible, and easier to maintain. The following C++ program demonstrates both inheritance and polymorphism by creating a base class named `Shape` and three derived classes named `Circle`, `Rectangle`, and `Triangle`. Each derived class overrides the virtual `area()` function of the base class to calculate the area of its respective shape. In the program, the `Shape` class acts as the base class. It contains a virtual function named `area()`. The keyword `virtual` is important because it enables runtime polymorphism. A virtual function tells the C++ compiler that the function can be overridden in derived classes and that the appropriate version of the function should be selected at runtime according to the actual object being referred to. The program can be written as follows: ```cpp #include using namespace std; class Shape { public: virtual double area() { return 0; } }; class Circle : public Shape { private: double radius; public: Circle(double r) { radius = r; } double area() override { return 3.14159 * radius * radius; } }; class Rectangle : public Shape { private: double length; double width; public: Rectangle(double l, double w) { length = l; width = w; } double area() override { return length * width; } }; class Triangle : public Shape { private: double base; double height; public: Triangle(double b, double h) { base = b; height = h; } double area() override { return 0.5 * base * height; } }; int main() { Shape *shape; Circle c(5); Rectangle r(10, 4); Triangle t(8, 6); shape = &c; cout << "Area of Circle