Exercises
2.4. Exercises#
Many of these exercises are taken from past exams of ECE 244 Programming Fundamentals courses at University of Toronto. The solutions are provided in the answer boxes.
Headings in this page classify the exercises into different categories: [Easy], [Intermediate], and [Challenging]. I suggest you start by easy exercises and work your way up to the challenging ones.
Question 7 in Fall 2021 Midterm Exam [Easy]
Consider the class definition shown below. Assume that iostream and string are included, and that the std namespace is used. Also assume that the class is correctly implemented.
class Book {
public:
Book() { cout << "A new book is added." << endl; }
Book(string s) {
cout << "Book " << s << " is added." << endl;
name = s;
}
~Book() { cout << "Book " << name << " is removed." << endl; }
private:
string name = "ECE244";
};
What is the output of the following main function?
Book* b1;
int main() {
Book b2;
Book* b3 = new Book("Pride and Prejudice");
if (true) {
b1 = new Book();
Book b4("Wuthering heights");
delete b3;
Book* b5 = new Book[2];
}
delete b1;
return 0;
}
Answer
A new book is added. Book Pride and Prejudice is added. A new book is added. Book Wuthering heights is added. Book Pride and Prejudice is removed. A new book is added. A new book is added. Book Wuthering heights is removed. Book ECE244 is removed. Book ECE244 is removed.
Explanation
A new book is added.
declaring b2 calls the default constructor
Book Pride and Prejudice is added.
new calls the second constructor
A new book is added.
new calls default constructor for b1
Book Wuthering heights is added.
b4 declaration calls the second constructor
Book Pride and Prejudice is removed.
delete b3 would call the destructor for what b3 is pointing at.
A new book is added. A new book is added.
new Book[2] calls the default constructor twice.
Book Wuthering heights is removed.
b4 goes out of scope and destructor is called.
Book ECE244 is removed.
delete b1 would call the default destructor.
Book ECE244 is removed.
Default destructor for b2 is called as we return from main, and b2 goes out of scope.
We don’t have delete b5, and hence the destructor is not called for the two-element array.
Question 1 in Fall 2022 Midterm Exam [Easy]
Consider the following C++ program. There are three statements in the main function: A, B, and C. Which of these three statements will trigger compile-time errors?
class ECE244 {
private:
int num_student;
int num_TA;
int get_num_instructor();
public:
int num_instructor;
int get_num_student();
int get_num_TA();
};
int main() {
ECE244 year2022;
int num_student = year2022.num_student; // Statement A
int num_TA = year2022.get_num_TA(); // Statement B
int num_instructor = year2022.get_num_instructor(); // Statement C
return 0;
}
Answer
A, C
In statement A, num_student is a private data member and cannot be accessed outside the class.
In statement C, get_num_instructor() is a private function member, and cannot be accessed outside the class.
Modified Question 9 in Fall 2018 Midterm Exam [Challenging]
Consider the following definition/implementation of a class called Shape that appears in the file: Shape.h.
Shape.h
#include <iostream>
using namespace std;
class Shape {
private:
int ID;
public:
Shape() {
ID = 0;
cout << "Constructor 1 " << ID << endl;
}
Shape(int id) {
ID = id;
cout << "Constructor 2 " << ID << endl;
}
~Shape() { cout << "Destructor " << endl; }
int getID() const { return ID; }
void setID(int id) { ID = id; }
};
The following is a main program that uses the above class.
main.cpp
#include <iostream>
#include "Shape.h"
using namespace std;
int getShapeID(Shape& s) {
return s.getID();
}
int main() {
Shape circle(5);
Shape line2[2];
cout << circle.getID() << endl;
cout << getShapeID(line2[1]) << endl;
return 0;
}
What is the output of the program? Select one of the answers from the table below.
Answer
Constructor 2 5 Constructor 1 0 Constructor 1 0 5 0 Destructor Destructor Destructor
Note that the destructor is called when an object goes out of scope.