Question

include #include using namespace std; class baseClass { public: void print() const; baseClass(strin… # What is the output of the following C++ program? #include #include using namespace std; class baseClass { public: void print() const; baseClass(string s = " ", int a = 0); //Postcondition: str = s; x = a; protected: int x; private: string str; }; class derivedClass: public baseClass { public: void print() const; derivedClass(string s = "", int a = 0, int b = 0); //Postcondition: str = s; x = a; y = b; private: int y; }; int main() { baseClass baseObject("This is the base class", 2); derivedClass derivedObject("DDDDDD", 3, 7); baseObject.print(); derivedObject.print(); return 0; } void baseClass::print() const { cout << x << " " << str << endl; } baseClass::baseClass(string s, int a) { str = s; x = a; } void derivedClass::print() const { cout << "Derived class: " << y << endl; baseClass::print(); } derivedClass::derivedClass(string s, int a, int b) :baseClass("Hello Base", a + b) { y = b; }

Short answer

The output is: 2 This is the base class Derived class: 7 10 Hello Base

Step-by-step solution

Analyze Main Function

In the `main()` function, two objects are created: `baseClass` with the arguments ("This is the base class", 2), and `derivedClass` with the arguments ("DDDDDD", 3, 7). Each of these objects then uses the `print()` function to display specific outputs.

Understand Base Class Initialization and Print

In `baseClass`, the constructor sets `str` to the provided string and `x` to the provided integer. So, `baseObject` is initialized with `str = "This is the base class"` and `x = 2`. The `print()` function in this class outputs `x` followed by `str`, separated by a space.

Explore Derived Class Initialization and Overrides

The `derivedClass` constructor calls the `baseClass` constructor with parameters ("Hello Base", 3 + 7). Thus, `str` becomes "Hello Base", `x` becomes 10, and `y`, specific to `derivedClass`, is set to 7. The `print()` function for `derivedClass` outputs "Derived class: " followed by `y`, then calls the base class's `print()` method.

Determine Output from Function Calls

The `print()` function for `baseObject` outputs `2 This is the base class`. For `derivedObject`, it outputs `Derived class: 7` followed by `10 Hello Base` due to how the print functions are supposed to work in both `baseClass` and `derivedClass`.

Key concepts

C++ constructors

In C++, constructors are special member functions that are invoked when a new object of a class is created. They play a crucial role in setting up initial values for an object. Constructors ensure that objects are initialized properly before they are used.

• Default Constructor: This is a constructor that can be called with no arguments. In our example, the constructors for both `baseClass` and `derivedClass` have default parameters, allowing objects to be created even without explicit argument passing.
• Parameterized Constructor: This allows you to provide specific values during the object's creation. The constructors in the example, `baseClass(string s, int a)` and `derivedClass(string s, int a, int b)`, demonstrate how parameters can be passed to set the initial state of the object.


• Initialization List: In `derivedClass`, you can see the use of an initialization list to explicitly call `baseClass`'s constructor. This helps in setting up inherited class members before any operations are performed within the `derivedClass` constructor block.

Understanding how constructors work is essential to utilizing C++ as it ensures objects are ready-to-use with expected states.

Class inheritance

Inheritance in C++ enables one class to acquire properties and behaviors of another class. This concept reflects the real world where objects can share characteristics and be grouped into types.

• Base Class: The `baseClass` in the example functions as the parent class. It defines properties and methods that can be shared or extended by other classes.
• Derived Class: The `derivedClass` inherits from `baseClass` using the ':' syntax (`class derivedClass : public baseClass`). This allows `derivedClass` to reuse and override the functionality defined in `baseClass`.
• Access Specifiers: It's important to note the use of public inheritance here, which means the public members of `baseClass` become public members of `derivedClass`. Protected members of `baseClass` are accessible within `derivedClass`, but private members stay inaccessible.

With inheritance, code redundancy is reduced, and a robust, structured approach in programming can be achieved.

Function overriding

Function overriding in C++ occurs when a derived class provides its own implementation for a member function that is already defined in its base class. This allows derived classes to offer specific behavior for the shared function signature seen in the base class.

• Base Class Function: The `print` function in `baseClass` displays information relevant to the base object. In the example, it outputs the integer `x` followed by the string `str`.
• Overridden Function: In `derivedClass`, the `print` function is overridden, but it still uses the `print` function from `baseClass` by calling `baseClass::print()`. This demonstrates how a derived class can extend or modify existing functionality while integrating the base class behavior.

Overriding ensures that the derived class can fully implement its behavior while maintaining compatibility with the general interfaces provided by the base class. It is a powerful feature in C++ to achieve polymorphism, allowing objects to be manipulated through interfaces they share while executing specific behaviors.