7.1. 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 5 in Fall 2019 Midterm Exam [Easy]

Consider a (non-member) function called doIt, which takes a single object of type DayOfYear and returns a single object also of type DayOfYear. You may assume that the class DayOfYear is correctly implemented and that DayOfYear.h is included. Which of the following implementations of this function is problem-free?

1. DayOfYear doIt(DayOfYear& arg) {
     DayOfYear temp;
     temp = arg;
     return (arg);
   }
   

   Answer

   Has no problem. We return arg by value and we create a copy of arg using copy constructor.

2. DayOfYear doIt(DayOfYear& arg) {
     DayOfYear temp;
     temp = arg;
     return (temp);
   }
   

   Answer

   Has no problem. We return temp by value and we create a copy of temp using copy constructor.

3. DayOfYear& doIt(DayOfYear& arg) {
     DayOfYear temp;
     temp = arg;
     return (*this);
   }
   

   Answer

   Has a problem, because in the question it says doIt is a non-member function. Since this is a pointer to an object on which the member function is invoked, it can only be accessed in a member function. In short, we cannot access this in doIt function.

4. DayOfYear& doIt(DayOfYear& arg) {
     DayOfYear temp;
     temp = arg;
     return (temp);
   }
   

   Answer

   Has a problem, but it is quite tricky. temp is a local only to the function doIt since it was defined only inside the function. temp will go out of scope or disappear from the memory the moment we return from doIt function. If we return temp by reference, and temp actually is non-existing after the function call, the behavior is undefined if we try accessing whatever doIt returns.

Question 5 in Fall 2019 Final Exam [Intermediate]

Consider the following class definition and implementation.

#include <iostream>
using namespace std;

class Duo {
 private:
  int* p;
  int* q;

 public:
  Duo(int a, int b) {
    p = new int;
    *p = a;
    q = new int;
    *q = b;
  }
  int get_a() { return *p; }
  int get_b() { return *q; }
  void set_a(int a) { *p = a; }
  void set_b(int b) { *q = b; }
  Duo funnyMultiply(Duo& rhs) {
    Duo temp(0, 0);
    *(temp.p) = (*p) * *(rhs.p);
    *(temp.q) = (*q) * *(rhs.q);
    *(rhs.p) = *(rhs.p) - 1;
    *(rhs.q) = *(rhs.q) - 1;
    return (temp);
  }
  Duo print() {
    cout << *p << " " << *q << endl;
    return (*this);
  }
};

The following main program uses class Duo.

int main() {
  Duo X(3, 5);
  Duo Y(8, 9);
  Duo Z(2, 4);
  Z = X.funnyMultiply(Y);
  Z.print();  // Statement 1
  Z.set_a(1);
  Z.set_b(2);
  Z.print();  // Statement 2
  X.print();  // Statement 3
  Y.print();  // Statement 4
  Duo W(6, 12);
  Duo V(2, 3);
  W.print().funnyMultiply(V).print();  // Statement 5
  W.print();                           // Statement 6
  // Point A
  cout << "Program is done" << endl;
  return (0);
}

1. Write the output produced by each of the labeled statement (Statement 1 to Statement 6) in main. Write your answer in the table below.

   Grade	Output
   Statement 1
   Statement 2
   Statement 3
   Statement 4
   Statement 5
   Statement 6

   Answer

   Grade	Output
   Statement 1	24 45
   Statement 2	1 2
   Statement 3	3 5
   Statement 4	7 8
   Statement 5	6 12 12 36
   Statement 6	6 12

2. How many integers exist in memory in the form of a memory leak when execution reaches Point A in the main function above? Write your answer in the box below.

   Answer

   Z initially had p and q pointing to two integers, and we lost access to them when we pointed to p and q from the object returned by value in Z = X.funnyMultiply(Y);.

   Another two integers were lost in W.print().funnyMultiply(V).print(); after returning from funnyMultiply function.

   Total, we have 4 integers in the memory exist in the form of a memory leak.

In progress!