Question

Write a class declaration named Circle with a private member variable named radius. Write set and get functions to access the radius variable, and a function named get Area that returns the area of the circle. The area is calculated as 3.14159 * radius * radius

Short answer

Answer: The main purpose of the Circle class is to model a circle with a specified radius. It provides set and get functions to access the radius value and a function named getArea to calculate the area of the circle. The area of the circle is calculated using the formula 3.14159 * radius * radius in the getArea function.

Step-by-step solution

Declare Circle class

Declare a new class named 'Circle' using the class keyword. class Circle { // class members will go here };

Define private member variable

Inside the Circle class, define the private member variable named 'radius' with the appropriate data type (double). private: double radius;

Write set and get functions

Inside the Circle class, write the public functions named 'setRadius' and 'getRadius'. The setRadius function should take a double argument and set the radius to the given value. The getRadius function should return the radius value. public: void setRadius(double r) { radius = r; } double getRadius() { return radius; }

Write getArea function

Inside the Circle class, write the public function named 'getArea'. The getArea function should calculate the area of the circle using the formula 3.14159 * radius * radius and return the result. public: double getArea() { return 3.14159 * radius * radius; } Here's the complete Circle class declaration, following the steps above: ```cpp class Circle { private: double radius; public: void setRadius(double r) { radius = r; } double getRadius() { return radius; } double getArea() { return 3.14159 * radius * radius; } }; ```

Key concepts

Object-Oriented Programming

Object-oriented programming, or OOP, is a programming paradigm where you model real-world objects as classes in your code. In this exercise, we created a `Circle` class. Classes are blueprints that define the properties and behaviors (data and methods) an object will have. OOP helps to make code more modular and reusable.

• **Classes and Objects:** In OOP, a class is like a blueprint, and an object is an instance of that blueprint. Once a `Circle` class is defined, you can create multiple circle objects, each with its own radius.
• **Modularity:** Code is organized into classes, making it easier to manage and modify. For instance, if you want to add a new feature, like calculating the circumference of a circle, you'd only need to update the `Circle` class.
• **Encapsulation and Abstraction:** OOP lets you hide complex implementation details. Instead of knowing how `getArea` calculates the area, when using it, you only need to know it returns the area of the circle.

OOP makes it simpler to structure complex applications, as it mimics how we naturally think about the world by focusing on entities (objects) and their interactions.

Member Functions

Member functions are functions defined inside a class in C++. They perform operations using the data of the class, and they can manipulate or retrieve the class data. The `Circle` class in our exercise includes three member functions: `setRadius`, `getRadius`, and `getArea`.

• **setRadius:** This function accepts a parameter and is used to modify the private `radius` variable. It's a common practice to have a setter function to control changes to member variables.
• **getRadius:** This function returns the value of the `radius`. It provides controlled access to the private data members of the class, ensuring that `radius` can only be accessed through this function.
• **getArea:** The purpose of this function is to compute the area of the circle using the formula \(\pi \times \text{radius}^2\). It demonstrates how member functions can use the class's other member variables.

Including member functions in your classes enhances encapsulation and ensures that data is handled in a controlled manner, which is a key aspect of clean and maintainable code.

Data Encapsulation

Data encapsulation is one of the fundamental concepts of object-oriented programming. It involves bundling data with the methods that operate on that data. In our `Circle` class example, we use encapsulation to hide the `radius` variable by making it private. Here's how it works and why it's useful:

• **Privacy and Security:** By keeping the `radius` variable private, we prevent direct access from outside the class. This protects the inner workings of our `Circle` object, ensuring that `radius` can only be modified via the `setRadius` method.
• **Control:** Encapsulation provides control over the data. We can add checks in our `setRadius` method, to ensure the radius value makes sense, such as not allowing negative numbers.
• **Maintainability:** With encapsulation, any changes to how data is managed internally don't affect how other parts of your code interact with `Circle` objects. For example, if you update the way `getArea` calculates an area, the change is internal to the class usage.

Encapsulation is essential in managing complexity in code. It secures the internal representation of objects from unexpected access and manipulation from the outside, promoting robust and maintainable applications.