11.1. 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 11 in Fall 2018 Final Exam [Easy]

Consider the following class definitions and implementations, as well as a main function that uses them. All the code appears in one file and it compiles with no errors.

#include <iostream>
using namespace std;

class firstOne {
 private:
  int x;
  char* first;

 public:
  firstOne();
  firstOne(const char* s);
};

class secondOne : public firstOne {
 private:
  int y;
  char* second;

 public:
  secondOne(const char* s);
  secondOne(int v);
};

firstOne::firstOne() {
  x = 0;
  first = new char[1];
  *first = '\0';
  cout << "Constructor 1 of firstOne done" << endl;
}

firstOne::firstOne(const char* s) {
  x = 0;
  int size = strlen(s);
  first = new char[size + 1];
  strcpy(first, s);
  cout << "Constructor 2 of firstOne done" << endl;
}

secondOne::secondOne(const char* s) {
  y = 0;
  int size = strlen(s);
  second = new char[size + 1];
  strcpy(second, s);
  cout << "Constructor 1 of secondOne done" << endl;
}

secondOne::secondOne(int v) : firstOne("X") {
  y = v;
  second = new char[1];
  *second = '\0';
  cout << "Constructor 2 of secondOne done" << endl;
}

int main() {
  firstOne a;
  firstOne b("G");
  secondOne c("N");
  secondOne d(8);
  return 0;
}

Indicate what each statement in the above main function prints, using the table below. If no output is produced, write “NONE”.

Statement

Output

firstOne a;

firstOne b("G");

secondOne c ( "N");

secondOne d(8);

Answer

Statement

Output

firstOne a;

 

Constructor 1 of firstOne done

firstOne b("G");

 

Constructor 2 of firstOne done

secondOne c ( "N");

 

Constructor 1 of firstOne done
Constructor 1 of secondOne done

secondOne d(8);

 

Constructor 2 of firstOne done
Constructor 2 of secondOne done

Question 14 in Fall 2019 Final Exam [Easy]

Consider the following class definitions and implementations of classes, Shape and Circle. They are followed by a main function that utilizes these classes.

#include <iostream>
using namespace std;
class Shape {
 protected:
  int shapeID;

 public:
  int getID() { return shapeID; }
  void setID(int k) { shapeID = k; }
  virtual void draw() = 0;
  virtual void print() = 0;
};
class Circle : public Shape {
 protected:
  float radius;

 public:
  float getRadius() { return radius; }
  void setRadius(float r) { radius = r; }
  virtual void draw() {
    // code to draw
  }
};
class Rectangle : public Shape {
 protected:
  float length;
  float width;

 public:
  float getLength() { return length; }
  void setLength(float x) { length = x; }
  float getWidth() { return width; }
  void setWidth(float x) { width = x; }
  virtual void draw() {
    // Code to draw
  }
  virtual void print() {
    // Code to print
  }
};

int main() {
  // Statements in the main function return 0;
}

Indicate which of the following statements that appear in the main function compile with no errors or produce a compile time error.

Indicate also the reason in the table below.

Code snippet

Does the code snippet compile? If yes, Why?

Shape s;

Circle c;

Rectangle r;
r.setID(9)

Rectangle d;
d.length = 3.0;

Answer

Code snippet

Does the code snippet compile? If yes, Why?

Shape s;

No, an object of an abstract class cannot be created

Circle c;

No, Circle is an abstract class too as it doesn’t implement print

Rectangle r;
r.setID(9)

Yes

Rectangle d;
d.length = 3.0;

No, Rectangle::length is a protected data member that cannot be accessed outside the class

Question 12 in Fall 2018 Final Exam [Intermediate]

Consider the following base and derived classes. They compile with no errors.

#include <iostream>
#include <string>
using namespace std;

class Dessert {
 protected:
  int price = 0;

 public:
  Dessert() { cout << "we have dessert\n"; }
  ~Dessert() { cout << "no more dessert\n"; }
  void print() { cout << "dessert unknown\n"; }
  virtual int cost() = 0;
};

class Candy : public Dessert {
 protected:
  int weight_in_grams;

 public:
  Candy(int grams, int per_gram) {
    weight_in_grams = grams;
    price = per_gram;
    cout << "we have candy\n";
  }
  ~Candy() { cout << "no more candy\n"; }
  void print() {
    cout << "Candy: " << weight_in_grams << " grams, at " << price
         << " cents per gram\n";
  }
  virtual int cost() { return weight_in_grams * price; }
};

class Cookies : public Dessert {
 protected:
  int num_dozens;

 public:
  Cookies(int dozens, int per_dozen) {
    num_dozens = dozens;
    price = per_dozen;
    cout << "We have cookies\n";
  }
  ~Cookies() { cout << "no more cookies\n"; }
  void print() {
    cout << "Cookies: " << num_dozens << "dozens, at " << price
         << " cents per dozen\n";
  }
  virtual int cost() { return num_dozens * price; }
};

class IceCream : public Dessert {
 protected:
  string flavor = "vanilla";
  int scoops;

 public:
  IceCream(string fly, int scps, int per_scoop) {
    flavor = fly;
    scoops = scps;
    price = per_scoop;
    cout << "we have " << flavor << " Ice Cream\n";
  }
  ~IceCream() { cout << "no more ice cream\n"; }
  void print() {
    cout << "Ice Cream: " << scoops << " scoops, at " << price
         << " cents per scoop\n ";
  }
  virtual int cost() { return scoops * price; }
};

class Sundae : public IceCream {
 protected:
  int topings_cost;

 public:
  Sundae(string flv, int scps, int per_scoop, int tps)
      : IceCream(flv, scps, per_scoop) {
    topings_cost = tps;
    cout << " with topings\n";
  }
  ~Sundae() { cout << "no more sundae\n"; }
  void print() {
    IceCream::print();
    cout << " topings cost is: " << topings_cost << endl;
  }
  virtual int cost() { return scoops * price + topings_cost; }
};

Consider each of the following main functions that use the above classes. You may assume that each main function includes the code of the classes above, including the #include’s and the using namespace std;

For each main function, indicate if the function compiles with no errors or not (ignore warnings). If the function compiles with no errors, then indicate the output produced by the function?

  1. int main() {
  Dessert a;
  Cookies b(2, 300);
  IceCream c("Vanilla", 2, 350);
  return 0;
}

    Does the program compile with no errors? If it does compile with no errors, what is the output produced by the execution?

    Answer

    No, it doesn’t compile.

    We cannot create objects of abstract classes.

  2. int main() {
  Dessert* pc;
  IceCream* pi;
  pc = new Cookies(2, 250);
  pi = new IceCream("mint", 1, 250);
  delete pc;
  delete pi;
  return 0;
}

    Does the program compile with no errors? If it does compile with no errors, what is the output produced by the execution?

    Answer

    Yes, the program compiles.

    Output

    we have dessert
We have cookies
we have dessert
we have mint Ice Cream
no more dessert
no more ice cream
no more dessert

    delete pc calls the destructor of Desert only as pc is a pointer of type Desert. We cannot access the destructor of Cookies through pc.

    delete pi calls the destructor of IceCream first, then the destructor of Desert. pi is of type IceCream, and through it we can access both destructors.

  3. int main() {
  Sundae* ps;
  IceCream* pi;
  pi = new IceCream("mint", 1, 250);
  ps = pi;
  delete ps;
}

    Answer

    No, the program doesn’t compile.

    ps = pi; is not valid. Sundae is derived from IceCream. ps cannot point to an object IceCream, as it cannot access its members that don’t exist.

  4. int main() {
  Dessert* ps = new IceCream("vanilla", 2, 350);
  cout << ps->cost() << endl;
  return 0;
}

    Answer

    Yes, the program compiles.

    Output

    we have dessert
we have vanilla Ice Cream
700

    ps->cost() will call the cost() of IceCream as cost() is a virtual function, hence ps will call the function according to the type of the object, not the pointer.

Question 15 in Fall 2019 Final Exam [Easy]

Consider the following class definitions.

class BaseC {
 private:
  int a;
  void help();

 protected:
  int b;

 public:
  int c;
  int d;
  void print();
};

class DerivedC : public BaseC {
 private:
  int x;
  void nohelp();

 public:
  int w;
  int z;
  void noprint();
};

The following declaration appears in the nohelp member function of the class DerivedC.

DerivedC derived;

Indicate whether the following statements is correct code (i.e., compiles with no errors), or incorrect code (i.e., generates a compile time error). Assume the statements in the rows of the table also appear in the nohelp member function of the class DerivedC.

Statement

Correct/Incorrect

derived.a = 8;

derived.b = 10;

derived.x = 12;

derived.w = 4;

Answer

Statement

Correct/Incorrect

derived.a = 8;

Incorrect (a is a private member of the Base class)

derived.b = 10;

Correct (b is protected in Base and can be access in DerivedC)

derived.x = 12;

Correct (x is private member of the DerivedC class and can be accessed in DerivedC)

derived.w = 4;

Correct (w is a public member of DerivedC)

Question 16 in Fall 2019 Final Exam [Intermediate]

Consider the following base and derived classes. They compile with no errors.

#include <iostream>
#include <string>

using namespace std;

class CircuitElement {
 protected:
  int code;

 public:
  CircuitElement() { cout << "circuit element\n"; }
  CircuitElement(int c) {
    code = c;
    cout << "circuit element with code\n";
  }
  ~CircuitElement() { cout << "no circuit element\n"; }
  float getPower() { return 0.0; }
  virtual void print() { cout << "error\n"; }
};

class Resistor : public CircuitElement {
 protected:
  int resistance;

 public:
  Resistor(int r) {
    code = 1;
    resistance = r;
    cout << "resistor\n";
  }
  ~Resistor() { cout << "no resistor\n"; }
  float getPower() { return 0.0; }
  void print() { cout << "Resistor: " << resistance << endl; }
};

class Capacitor : public CircuitElement {
 protected:
  int capacitance;

 public:
  Capacitor(int c) : CircuitElement(2) {
    capacitance = c;
    cout << "capacitor\n";
  }
  float getPower() { return 0.0; }
  ~Capacitor() { cout << "no capacitor\n"; }
  void print() { cout << "Capacitor: " << capacitance << endl; }
};

class PowerResistor : public Resistor {
 protected:
  float power;

 public:
  PowerResistor(int r, float p) : Resistor(r) {
    power = p;
    cout << "power resistor\n";
  }
  ~PowerResistor() { cout << "no power resistor\n"; }
  float getPower() { return power; }
  virtual float powerResistance() { return (power * resistance); }
  void print() {
    Resistor::print();
    cout << "Power resistor: " << power << endl;
  }
};

class PowerCapacitor : public Capacitor {
 protected:
  float power;

 public:
  PowerCapacitor(int c, float p) : Capacitor(c) {
    power = p;
    cout << "power capacitor\n";
  }
  ~PowerCapacitor() { cout << "no power capacitor\n"; }
  float getPower() { return power; }
  virtual float powerCapacitance() { return (power * capacitance); }
  void print() {
    Capacitor::print();
    cout << "Power capacitor: " << power << endl;
  }
};

Consider each of the following main functions that use the above classes. You may assume that each main function includes the code of the classes above, including the #include’s and the using namespace std;.

For each main function, if the function compiles with no errors (ignore warnings), then write the output produced by the function. If the function compiles with errors, then write: “compile errors”.

  1. int main() {
  Capacitor c(150);
  PowerResistor p(180, 350);
  return 0;
}

    Answer

    circuit element with code
capacitor
circuit element
resistor
power resistor
no power resistor
no resistor
no circuit element
no capacitor
no circuit element

    We assume that p is destructed before c.

  2. int main() {
  CircuitElement* pr;
  pr = new PowerResistor(200, 250);
  delete pr;
  return 0;
}

    Answer

    circuit element
resistor
power resistor
no circuit element

    The tricky part is that delete pr will execute the destructor of the type of pr, since the destructor is not a virtual function.

  3. int main() {
  Capacitor* c;
  c = new CircuitElement(5);
  delete c;
  return 0;
}

    Answer

    Compile-time error for line c = new CircuitElement(5);, as you cannot make a pointer to a derived object c point to a base object CircuitElement.

  4. int main() {
  PowerResistor* pr;
  Resistor* r;
  r = new Resistor(450);
  pr = r;
  delete pr;
  return 0;
}

    Answer

    Compile-time error for line pr = r;, as pr is a pointer of derived object that cannot point to a base object.

  5. int main() {
  PowerResistor r(250, 1000);
  CircuitElement e;
  e = r;
  return 0;
}

    Answer

    circuit element
resistor
power resistor
circuit element
no circuit element
no power resistor
no resistor
no circuit element

    We assume we destruct e then p. It is possible to do e = r as e is a base object and r is derived.

  6. int main() {
  CircuitElement* e = new PowerCapacitor(500, 1000);
  e->print();
  return 0;
}

    Answer

    circuit element with code
capacitor
power capacitor
Capacitor: 500
Power capacitor: 1000

    We can make a base object point to a derived object, hence CircuitElement* e = new PowerCapacitor(500, 1000); is possible.

    Since the print() function is virtual in CircuitElement, it is virtual in all derived classes. Therefore when e->print() is executed, the print() function of the object e is pointing, which is PowerCapacitor to is called.

  7. int main() {
  Capacitor* c = new PowerCapacitor(300, 100);
  cout << c->getPower() << endl;
  return 0;
}

    Answer

    circuit element with code
capacitor
power capacitor
0

    The getPower function is not virtual, therefore when c->getPower() is called we call the getPower function of Capacitor – the type of c.

    Since the memory is dynamically allocated and not freed, no destructors are called before returning from main.

  8. int main() {
  PowerResistor pr(20, 100);
  Resistor* r = &pr;
  cout << r->powerResistance() << endl;
  return 0;
  }

    Answer

    Compile-time error.

    The error exists at r->powerResistance(). powerResistance() is not a virtual function, hence when r->powerResistance() is executed, powerResistance() of Resistor is called. There is no member named powerResistance in Resistor class.

Question 5 in Fall 2022 Final Exam [Intermediate]:

The University of Toronto wants to manage students from different departments using a C++ program. Students from all departments will share the following base class:

class student {
 protected:
  string name;
  int id;

 public:
  student(const string& name_, int id_) : name(name_), id(id_) {
    cout << "student" << endl;
  };
  virtual void print_server() = 0;
  virtual void print_department() = 0;
  string get_name() { return name; }
  int get_id() { return id; }
};

Derived from student class, the programmers then write another class for engineering students. All engineering students have access to the ECF server:

class eng_student : public student {
 protected:
  int ecf_id;

 public:
  eng_student(const string& name_, int id_, int ecf_id_)
      : student(name_, id_), ecf_id(ecf_id_) {
    cout << "eng student" << endl;
  };
  virtual void print_server() { cout << name << " logs into ecf." << endl; }
  int get_ecf_id() { return ecf_id; }
};

Derived from eng_student, programmers then write two classes for ECE students and MIE students. Unlike MIE students, ECE students have their designated server called UG server:

class mie_student : public eng_student {
 public:
  mie_student(const string& name_, int id_, int ecf_id_)
      : eng_student(name_, id_, ecf_id_) {
    cout << "mie student" << endl;
  };
  virtual void print_department() {
    cout << name << " is a mie student." << endl;
  }
};

class ece_student : public eng_student {
 private:
  int ug_id;

 public:
  ece_student(const string& name_, int id_, int ecf_id_, int ug_id_)
      : eng_student(name_, id_, ecf_id_), ug_id(ug_id_) {
    cout << "ece student" << endl;
  };
  virtual void print_server() { cout << name << " logs into ug." << endl; }
  virtual void print_department() {
    cout << name << " is an ece student." << endl;
  }
  int get_ug_id() { return ug_id; }
};

In addition, programmers write a new derived class for Computer Science (CS) students. Unlike engineering students, they use Markus servers instead of ECF servers:

class cs_student : public student {
 protected:
  int markus_id;

 public:
  cs_student(const string& name_, int id_, int markus_id_)
      : student(name_, id_), markus_id(markus_id_) {
    cout << "cs student" << endl;
  }
  virtual void print_server() { cout << name << " logs into markus." << endl; }
  virtual void print_department() {
    cout << name << " is an cs student." << endl;
  }
  int get_markus_id() { return markus_id; }
};

Read the implementations of these five classes carefully and answer the following questions.

  1. You write the following piece of code to declare four students. However, you get a compile-time error. Why doesn’t it compile? (Note: you don’t need to fix anything in the class declarations and implementations given above.)

    cs_student A("A", 0, 10);
ece_student B("B", 1, 11, 0);
eng_student H("H", 3, 13);

    Answer

    student class is an abstract function. eng_student inherits from student class; however, it is an abstract class too as it did not implement print_department pure virtual function that was in student class.

  2. Now, an array named student_list is declared and initialized as follows. Write the output generated by std::cout.

    student* student_list[4] = {
  new cs_student("Leo", 0, 10), 
  new ece_student("Bill", 1, 11, 0),
  new mie_student("Ellie", 2, 12), 
  new ece_student("Haley", 3, 13, 1)
  };

    Answer

    student
cs student
student
eng student
ece student
student
eng student
mie student
student
eng student
ece student

    new cs_student("Leo", 0, 10) would call the constructor of the base class student, then derived class cs_student. This prints.

    student
cs student

    new ece_student("Bill", 1, 11, 0) would call the constructor of the base class student, then eng_student, then ece_student. This prints.

    student
eng student
ece student

    The same idea follows for new mie_student("Ellie", 2, 12) and new ece_student("Haley", 3, 13, 1).

  3. After the student_list initialized in question 2, the following for loops will be executed. What will be the output generated by these two loops?

    cout << "Department: " << endl;
for (int i = 0; i < 4; ++i) {
  student_list[i]->print_department();
}
cout << "Server: " << endl;
for (int i = 0; i < 4; ++i) {
  student_list[i]->print_server();
}

    Answer

    Department: 
Leo is an cs student.
Bill is an ece student.
Ellie is a mie student.
Haley is an ece student.
Server: 
Leo logs into markus.
Bill logs into ug.
Ellie logs into ecf.
Haley logs into ug.

    Since print_department(); and print_server() are virtual functions, the function invoked would be determined based on the type student_list[i] points to. In the student_list array, we have CS, ECE, MIE and ECE, and these would be the objects on which the functions get invoked.