Question

Consider the following statements: class yClass class xClass: public yClass { { public: public: void one(); void one(); void two(int, int); xClass(); yClass(); private: private: int z; int a; int b; }; }; Suppose the following statements are in a user program (client code): yClass y; xClass x; a. The private members of yClass are public members of xClass. True or False? b. Mark the following statements as valid or invalid. If a statement is invalid, explain why. i. void yClass::one() { cout << a + b << endl; } ii. y.a = 15; x.b = 30; iii. void xClass::one() { a = 10; b = 15; z = 30; cout << a + b + z << endl; } iv. cout << y.a << " " << y.b << " " << x.z << endl;

Short answer

a. False. i. Valid. ii. Invalid, `a` and `b` are private. iii. Valid. iv. Invalid, all members are private.

Step-by-step solution

Understanding Class Structures

Analyze the class definitions given in the problem. `yClass` has two methods `one()` and `two(int, int)` with private integer members `a` and `b`. `xClass` inherits from `yClass`, making it a derived class with its own constructor and an additional private member `z`.

Evaluating Statement a

Statement a asks whether the private members of `yClass` become public in `xClass`. In C++, private members of a base class are not accessible directly to any other class, including derived classes. Thus, the private members `a` and `b` of `yClass` remain private and do not become public in `xClass`.

Analyzing Statement b.i

The line `void yClass::one() { cout << a + b << endl; }` is valid because it is a definition of the `one()` function within `yClass`, which has direct access to its private members `a` and `b`. There is no scope issue in this block of code.

Analyzing Statement b.ii

The statements `y.a = 15;` and `x.b = 30;` are invalid because both `a` and `b` are private members of `yClass` and hence cannot be accessed directly by any object instances of `yClass` or its derived class `xClass` from outside the class.

Analyzing Statement b.iii

The line `void xClass::one() { a = 10; b = 15; z = 30; cout << a + b + z << endl; }` is valid. The function `one()` is within the scope of `xClass`, and since `xClass` inherits from `yClass`, it can access `a`, `b`, and `z` (as `z` is its own member). Private inheritance matters when accessing them from outside this method, but in member functions, methods can access all private members of itself or any of its base class directly.

Analyzing Statement b.iv

The statement `cout << y.a << " " << y.b << " " << x.z << endl;` is invalid. This is because `a`, `b` of `yClass`, and `z` of `xClass` are private and cannot be accessed directly from an object instance through the `cout` operation.

Key concepts

Object-Oriented Programming

C++ is a versatile programming language that strongly emphasizes Object-Oriented Programming (OOP). OOP is a paradigm centered around objects, which are instances of classes that encapsulate data and functionality. It encourages software design that is modular, maintainable, and reusable. Key concepts in OOP include:

• Encapsulation: Data and functionalities are bundled together in objects. This helps protect the internal state of an object from unwanted external interference.
• Abstraction: Simplifying complex systems by modeling classes appropriate to the problem.
• Inheritance: Enables new classes to adopt properties of existing classes, promoting code reuse.
• Polymorphism: Allows objects to be interpreted as instances of their parent class, facilitating flexibility and integration without altering existing codebases.

Understanding these concepts thoroughly helps in applying them effectively in writing efficient and clean copy code.

Access Specifiers

In C++, access specifiers are keywords that set the accessibility levels of class members. They define how the class members (attributes and methods) can be accessed, ensuring data integrity and security.

• Public: Members declared as public are accessible from anywhere outside the class scope, making them accessible to other classes and functions.
• Private: These members are only accessible within the class itself, safeguarding them from outside influence or misuse.
• Protected: Protected members work like private members, but they can also be accessed in derived classes. This is commonly used in inheritance scenarios.

Selecting the appropriate access specifier is crucial as it helps to maintain a proper encapsulated structure, ensuring that the functioning of the class remains as intended by the developer.

Class Definition

A class definition in C++ is a blueprint for creating objects. It comprises data members (attributes) and member functions (methods) that define behaviors.
To define a class, you encapsulate data members and methods between `class` keyword and braces `{}`. Inside, you can publicly define functions and privately define variables. This encapsulation aids in creating well-structured and robust software.
Here's a basic example: ```cpp class Sample { public: void display(); // public member function private: int number; // private data member }; ``` Objects are created from defined classes, acting as containers for data and behaviors. This allows the creation of multiple objects from one class blueprint, each with its own data.

Inheritance and Access Control

Inheritance in C++ is a critical feature that enables new classes to derive properties and behaviors from existing classes. This is valuable for code reuse and organization.
In C++, inheritance can be declared using the syntax `class DerivedClass : BaseClass`, which sets how inherited members from the base class can be accessed.

• Public Inheritance: Base class's public and protected members turn into Derived class's public and protected members, respectively.
• Protected Inheritance: Public and protected members of the Base class become protected in the derived class.
• Private Inheritance: Regardless of their original status, all inherited members become private in the derived class.

Understanding these nuances is essential for leveraging inheritance efficiently to construct a robust class hierarchy and maintain control over how properties and behaviors are extended to derived classes.