Question

Consider the following class definition: class circle class cylinder: public circle { { public: public: void print() const; void print() const; void setRadius(double); void setHeight(double); double getRadius(); double getHeight(); double area(); double volume(); circle(); double area(); circle(double); cylinder(); cylinder(double, double); private: private: double radius; double height; }; }; Suppose that you have the declaration: cylinder newCylinder;

Short answer

The object `newCylinder` of type `cylinder` is created using the `cylinder` default constructor.

Step-by-step solution

Understand the Class Definitions

There are two classes given: `circle` and `cylinder`. `cylinder` is derived from `circle`, implying inheritance. The `circle` class has a private data member `radius` and several public member functions including `setRadius`, `getRadius`, `area`, and two constructors. The `cylinder` class has its own private data member `height` in addition to inherited members and functions from `circle`, and it adds methods like `setHeight`, `getHeight`, `volume`, and its own `cylinder` constructor.

Identify Object Declaration

The declaration `cylinder newCylinder;` creates an object `newCylinder` of type `cylinder`. Since `cylinder` inherits from `circle`, `newCylinder` can access all public methods of `circle` and `cylinder`.

Determine Constructor Usage

When the object `newCylinder` is declared, the default constructor of the `cylinder` class, `cylinder()`, is invoked. Since `cylinder()` is a default constructor, it typically initializes the member variables to default values. Additionally, it might invoke the `circle` constructor to initialize `radius`, often ensuring that both `radius` and `height` have valid initial values.

Key concepts

Inheritance

Inheritance is a fundamental concept in Object-Oriented Programming. It allows one class, called the derived or child class, to inherit attributes and methods from another class, known as the base or parent class. This mechanism serves several purposes:

• It promotes code reusability by allowing the new class to use existing code from the base class.
• It enables polymorphism, which is the ability to call different functions from derived classes through the same interface.
• It establishes a hierarchical relationship between classes, which can replicate real-world relationships, like that of a circle and a cylinder.

In our example, the `cylinder` class inherits from the `circle` class. This means `cylinder` not only has its own attributes and methods, like `height` and `volume`, but also inherits `radius`, `setRadius`, and `area` from the `circle`. With inheritance, any changes or improvements made to the `circle` can automatically be reflected in the `cylinder`, illustrating how inheritance can simplify and streamline complex class designs.

Class Structure

A class is like a blueprint for creating objects, embodying both properties (attributes) and actions (methods) relevant to the concept it represents. In the given example, the `circle` class represents a circular shape in geometry. It has a private data member:

• `radius` which stores the measurement of the circle's radius.

It also includes public functions that allow interaction with its data in a controlled manner:
- `setRadius(double)`: Sets the value of the radius. - `getRadius()`: Returns the current value of the radius. - `area()`: Computes and returns the area of the circle. Similarly, the `cylinder` class extends the structure of `circle`. In addition to integrating the `circle`'s properties, it introduces:

• `height` to represent the cylinder's size along the longitudinal axis.

This class adds functionality specific to cylinders with functions such as `setHeight`, `getHeight`, and `volume` to calculate the space the cylinder occupies. The separation and organization of methods and properties highlight the class structure's ability to modularize and manage complexity in programming.

Object Declaration

Object declaration is the process of creating an instance of a class. When you declare an object, you are essentially saying "I want to use the blueprint of a class to create a specific instance." In this exercise, `cylinder newCylinder;` is our object declaration.
What does this achieve?

• An instance of the `cylinder` class, named `newCylinder`, is created in the memory.
• `newCylinder` can access all public methods available in both `cylinder` and `circle` due to inheritance.

Once declared, `newCylinder` can interact with the members functions, such as setting its radius and height, or computing its volume. Through object declaration, our abstract plan (the class) is brought to life, ready to perform computations and represent specific data, which emphasizes the power of Object-Oriented Programming in real-world applications.

Constructor Usage

A constructor is a special type of method designed for the initialization of an object. It shares the same name as the class and is invoked automatically when a new object instance is created. Constructors can be of several types, but the two most commonly used are:

• Default Constructor: Initializes objects with default values.
• Parameterized Constructor: Initializes objects with specific values provided at creation.

In our context, when you declare `cylinder newCylinder;`, the default `cylinder()` constructor is automatically called. This function is responsible for giving initial values to properties, like `height` in `cylinder`, and it might also take care of calling `circle`'s constructor to initialize `radius`. Constructors ensure that objects start in a legally valid state, which aids in preventing errors during the object's lifecycle. Understanding constructor usage equips programmers with the ability to customize object creation and to enforce consistency right from the point of their instantiation.