WEEK 14 · LAB 6

Lab 6 — Polymorphic Public Inheritance

Use one function to introduce a student and a teacher.

I. Objectives

Recognize a virtual function redefined in a derived class using override.
Observe different behavior when calling a virtual function through a base class reference.

Before the Lab

Weeks 7, 9, and 13: references, const member functions, virtual functions, and override. const Person& refers to the original object without copying it. Review the supplied virtual destructor before running the code; keep that line as provided.

II. Environment

A computer with Windows, macOS, or Linux.
Use OnlineGDB in C++ mode, or the C++ environment demonstrated in class.
Save your program as lab06.cpp. Use one source file for this lab.

Open OnlineGDB ↗

III. Tasks and Requirements

Complete the TODOs in the starter code, then compare your result with the expected output. The starter is intentionally unfinished.

Task 1 — Read the common interface

Person provides virtual introduce(). Student and Teacher each override it. showIntroduction() accepts a Person reference and calls introduce(). Keep this supplied structure.

Task 2 — Complete the two introductions

At TODO 1, print I am a student. At TODO 2, print I am a teacher. End each line with a newline. Keep const and override in the function declarations.

Task 3 — Observe and explain the two calls

Run main() and compare the two output lines. Then swap the two calls to showIntroduction() and run again; the output order should also swap. No pointers or dynamic allocation are needed.

Starter Code

Download .cpp

#include <iostream>

class Person {
public:
    virtual void introduce() const {
        std::cout << "I am a person." << '\n';
    }

    virtual ~Person() = default;
};

class Student : public Person {
public:
    void introduce() const override {
        // TODO 1: Print the student's introduction.
    }
};

class Teacher : public Person {
public:
    void introduce() const override {
        // TODO 2: Print the teacher's introduction.
    }
};

void showIntroduction(const Person& person) {
    person.introduce();
}

int main() {
    Student student;
    Teacher teacher;
    showIntroduction(student);
    showIntroduction(teacher);
    return 0;
}

Expected Output

Expected output after completing both introductions.

I am a student.
I am a teacher.

IV. Submission

Your completed lab06.cpp source file.
One or two screenshots showing your test results.
A short answer to each question below, in English or Chinese.

Two Short Questions

Why does the same showIntroduction() function produce two different messages?
Which class's introduce() runs when the argument is teacher?