Question

Consider the following class definitions: class baseClass { public: void print() const; int getX() const; baseClass(int a = 0); protected: int x; }; class derivedClass: public baseClass { public: void print() const; int getResult() const; derivedClass(int a = 0, int b = 0); private: int y; }; Suppose the definitions of the member functions of these classes are as follows: void baseClass::print() const { cout << "In base: x = " << x << endl; } baseClass::baseClass(int a) { x = a; } int baseClass::getX() const { return x; } void derivedClass::print() const { cout << "In derived: x = " << x << ", y = " << y << "; x + y = " << x + y << endl; } int derivedClass::getResult() const { return x + y; } derivedClass::derivedClass(int a, int b) : baseClass(a) { y = b; } What is the output of the following function main? int main() { baseClass baseObject(7); derivedClass derivedObject(3, 8); baseObject.print(); derivedObject.print(); cout << "****" << baseObject.getX() << endl; cout << "" << derivedObject.getResult() << endl; return 0; }

Short answer

The output is: In base: x = 7 In derived: x = 3, y = 8; x + y = 11 ****7 11

Step-by-step solution

Understand Class Constructors

In the code snippet, two classes are defined: `baseClass` and `derivedClass`. `baseClass` has a constructor that initializes `x` with the value of the passed argument `a`. `derivedClass` inherits from `baseClass` and initializes `y` with the value of the second argument `b`. Moreover, `derivedClass` calls `baseClass` constructor to initialize `x`. In the `main` function, `baseObject` of type `baseClass` is initialized with `7`, and `derivedObject` of type `derivedClass` is initialized with `3` for `x` and `8` for `y`.

Analyze the `baseClass::print` Function Call

The `print` function of `baseClass` outputs the value of `x`. When `baseObject.print()` is called, it outputs `In base: x =`, followed by the value of `x`, which is initialized to `7` for `baseObject`. Therefore, the output is: `In base: x = 7`.

Analyze the `derivedClass::print` Function Call

The `print` function of `derivedClass` outputs the values of `x` and `y`, and their sum. When `derivedObject.print()` is called, it outputs `In derived: x =`, followed by the value of `x` which is `3`, and `y` which is `8`, and their sum which is `11`. So the output is: `In derived: x = 3, y = 8; x + y = 11`.

Evaluate `baseClass::getX` Function Call

The `getX` function of the `baseClass` returns the value of `x`. For `baseObject`, this value is `7`. Therefore, the output for the statement `cout << "****" << baseObject.getX() << endl;` will be `****7`.

Evaluate `derivedClass::getResult` Function Call

The `getResult()` function of the `derivedClass` returns the sum of `x` and `y`. For `derivedObject`, `x` is `3` and `y` is `8`, thus their sum is `11`. Hence, the output is `11`.

Key concepts

Class Constructors

In C++, class constructors are special member functions that are invoked automatically when an object of the class is created. Their primary role is to initialize object attributes to appropriate values. In the context of the example, we see two constructors: one for the `baseClass` and another for the `derivedClass`. The `baseClass` constructor accepts an integer parameter and assigns it to the attribute `x`. This provides a straightforward way to set up the object during its creation.

Moreover, the `derivedClass` constructor is designed to initialize both `x` and `y`. Some interesting mechanics occur here because `derivedClass` inherits from `baseClass`. Hence, the `derivedClass` constructor needs to call the `baseClass` constructor to ensure all attributes are initialized. This is achieved through the syntax `: baseClass(a)` in the `derivedClass` constructor, setting up the inherited `x` value before assigning to `y`.

Constructors are pivotal as they define how objects come into being and ensure they're ready to use immediately after creation.

Function Overloading in C++

Function overloading is a core concept in C++ that allows multiple functions to have the same name with different parameters. Despite having the same name, these functions perform different tasks based on their signature, which includes the number or type of their parameters.

In our example, function overloading isn't directly shown but applies to how functions with the same name can behave differently once we expand our program. For instance, if the `print` function had multiple versions, each with different input parameters, function overloading would allow the correct version to be called based on the arguments provided.

• Function signatures depend on return type and parameter list.
• Enables polymorphic behaviors without altering the function name.
• Essential in creating intuitive interfaces.

Function overloading makes code resilient and flexible, leading to more elegant and understandable implementations.

Access Specifiers in C++

Access specifiers in C++ control the visibility and accessibility of class members. The common specifiers include `public`, `protected`, and `private`. In the provided code, `baseClass` uses `public` and `protected`, while `derivedClass` adds `private` to the list. Here's what they mean:

• `public`: These members are accessible from outside the class, allowing full access in programs. Both `print` and `getX` in `baseClass` are public.
• `protected`: Members are accessible within the class itself and by inherited classes. This is why `x` can be accessed and modified within `derivedClass`.
• `private`: Members are strictly accessible only within the defining class. In our scenario, `y` in `derivedClass` is private.

Understanding these specifiers is pivotal in fostering encapsulation. They allow architects to hide data and expose only necessary interfaces, ensuring robustness and integrity of the code.

Object-Oriented Programming Concepts

Object-Oriented Programming (OOP) in C++ is a paradigm that organizes code using objects rather than actions. OOP concepts like inheritance, encapsulation, and polymorphism are key to designing scalable systems.

In the exercise above, inheritance is exemplified by `derivedClass` extending `baseClass`. This means it inherits its behaviors and properties, promoting code reuse. Such hierarchy allows `derivedClass` to directly use `baseClass` methods and attributes, which exemplifies the relationship.

• **Encapsulation**: Protects data by restricting external access and modification using access specifiers.
• **Inheritance**: Allows a class to inherit attributes and methods from another, fostering reusability.
• **Polymorphism**: Not directly demonstrated here but allows using a single interface to represent different types.

OOP is about creating modular code through objects that can interact with one another autonomously, enabling more complex and maintainable architectures.