9.12. Multiple Choice Exercises

Q-1: Which of the following are variables of type Book?

struct Book {
  string title, author;
  int yearPublished;
  double price;
};

int main() {
  Book gatsby = { "The Great Gatsby", "F. Scott Fitzgerald", 1925, 4.75 };
  Book frankenstein = { "Frankenstein", "Mary Shelley", 1823, 5.99 };
  string flies = "Lord of the Flies";
  int year = 1954;
}

• gatsby

• gatsby is a Book.

• frankenstein

• frankenstein is a Book.

• flies

• flies is a string.

• year

• year is an int.

Q-2: Which of the following are instance variables of type Book?

struct Book {
  string title, author;
  int yearPublished;
  double price;
};

int main() {
  Book gatsby = { "The Great Gatsby", "F. Scott Fitzgerald", 1925, 4.75 };
  Book frankenstein = { "Frankenstein", "Mary Shelley", 1823, 5.99 };
  string flies = "Lord of the Flies";
  int year = 1954;
}

• gatsby

• gatsby is a Book, not an instance variable of Book.

• title

• title is an instance variable of Book.

• year

• year is an int declared in main, not an instance variable of Book.

• price

• price is an instance variable of Book.

Q-3: What is the output of the code below?

struct Book {
  string title, author;
  int yearPublished;
  double price;
};

void printBook (Book& b) {
  cout << "\"" << b.title << "\" by " << b.author << " (" << b.yearPublished << "), $" << b.price << endl;
}

int main() {
  Book mockingbird = { "To Kill a Mockingbird", "Harper Lee", 1960, 9.25 };
  double discountedPrice = 7.19;
  b.price = discountedPrice;
  printBook (mockingbird);
}

• To Kill a Mockingbird by Harper Lee (1960), $9.25

• Take a closer look at main. Was the price of the book modified?

• “To Kill a Mockingbird” by Harper Lee (1960), $9.25

• Take a closer look at main. Was the price of the book modified?

• “To Kill a Mockingbird” by Harper Lee (1960), $7.19

• The price was changed from $9.25 to $7.19.

• "To Kill a Mockingbird" by Harper Lee (1960), $7.19

• The \ are escape characters. Used in this context, they allow us to print quotation marks.

Q-4: What kind of function is printBook?

struct Book {
  string title, author;
  int yearPublished;
  double price;
};

void printBook (Book& b) {
  cout << "\"" << b.title << "\" by " << b.author << " (" << b.yearPublished << "), $" << b.price << endl;
}

int main() {
  Book dracula = { "Dracula", "Bram Stoker", 1897, 3.95 };
  printBook (dracula);
}

• Pure function

• printBook takes a Book as an object but it doesn’t modify it.

• Modifier function

• Does printBook modify the Book object?

• Fill-in function

• printBook takes one parameter, and its parameter is not an empty Book object.

• Fruitful function

• printBook does not return anything.

Q-5: What is wrong with the code below?

struct Book {
  string title, author;
  int yearPublished;
  double price;
}

void printBook (Book& b) {
  cout << "\"" << b.title << "\" by " << b.author << " (" << b.yearPublished << "), $" << b.price << endl;
}

void applyDiscount (const Book& b, double discount) {
  b.price -= discount;
}

int main() {
  Book godfather = { "The Godfather", "Mario Puzo", 1969, 10.90 };
  applyDiscount (godfather, 5.40);
  printBook (godfather);
}

• The struct definition is missing a semicolon at the end.

• It’s a common mistake to forget the semicolon at the end of struct definitions.

• We are not allowed to pass in a Book object by reference in printBook.

• We are allowed to do this. It’s usually a good idea to pass structures by reference since it won’t make copies of the structures, thus saving memory space.

• The keyword const needs to be removed in the function definition for applyDiscount.

• Since the applyDiscount function modifies the Book passed into it, we don’t it to be const.

• There are no errors with the code.

• There are a couple errors. Can you find them?

Q-6: What kind of function is applyDiscount?

struct Book {
  string title, author;
  int yearPublished;
  double price;
};

void printBook (Book& b) {
  cout << "\"" << b.title << "\" by " << b.author << " (" << b.yearPublished << "), $" << b.price << endl;
}

void applyDiscount (Book& b, double discount) {
  b.price -= discount;
}

int main() {
  Book godfather = { "The Godfather", "Mario Puzo", 1969, 10.90 };
  applyDiscount (godfather, 5.40);
  printBook (godfather);
}

• Pure function

• Does applyDiscount modify the Book object?

• Modifier function

• applyDiscount modifies the Book object by updating the price.

• Fill-in function

• applyDiscount does not take an empty Book object as a parameter.

• Fruitful function

• applyDiscount does not return anything.

Q-7: What is the output of the code below?

struct Point3D {
  double x, y, z;
};

void printPoint3D (const Point3D& p) {
  cout << "(" << p.x << ", " << p.y << ", " << p.z << ")" << endl;
}

void midpoint (const Point3D& p1, const Point3D& p2, Point3D p3) {
  p3.x = (p1.x + p2.x) / 2;
  p3.y = (p1.y + p2.y) / 2;
  p3.z = (p1.z + p2.z) / 2;
}

int main() {
  Point3D p1 = { 3.0, 5.0, 2.0 };
  Point3D p2 = { 6.0, 3.5, 9.3 };
  Point3D p3 = { 0.0, 0.0, 0.0 };
  midpoint (p1, p2, p3);
  printPoint3D (p3);
}

• (4.5, 4.25, 5.65)

• Look at the function declaration of midpoint carefully.

• (3.0, 5.0, 2.0)

• Look at the function declaration of midpoint carefully.

• (9.0, 8.5, 11.3)

• Look at the function declaration of midpoint carefully.

• (0, 0, 0)

• The last parameter in midpoint is not passed by reference, so a copy is made and changes are made to the copy, not the original.

Q-8: What kind of function is midpoint?

struct Point3D {
  double x, y, z;
};

void printPoint3D (const Point3D& p) {
  cout << "(" << p.x << ", " << p.y << ", " << p.z << ")" << endl;
}

void midpoint (const Point3D& p1, const Point3D& p2, Point3D& p3) {
  p3.x = (p1.x + p2.x) / 2;
  p3.y = (p1.y + p2.y) / 2;
  p3.z = (p1.z + p2.z) / 2;
}

int main() {
  Point3D p1 = { 3.0, 5.0, 2.0 };
  Point3D p2 = { 6.0, 3.5, 9.3 };
  Point3D p3 = { 0.0, 0.0, 0.0 };
  midpoint (p1, p2, p3);
  printPoint3D (p3);
}

• Pure function

• Does midpoint modify a Point3D object?

• Modifier function

• midpoint modifies the last Point3D object.

• Fill-in function

• midpoint takes an “empty” third Point3D and fills it with the average of the other two Point3D objects.

• Fruitful function

• midpoint does not return anything.

Q-9: What is the output of the code below?

struct Point3D {
  double x, y, z;
};

void printPoint3D (const Point3D& p) {
  cout << "(" << p.x << ", " << p.y << ", " << p.z << ")" << endl;
}

void midpoint (const Point3D& p1, const Point3D& p2, Point3D& p3) {
  p3.x = (p1.x + p2.x) / 2;
  p3.y = (p1.y + p2.y) / 2;
  p3.z = (p1.z + p2.z) / 2;
}

Point3D reflectXYPlane(const Point3D& p) {
  Point3D flipped = p;
  flipped.z = -flipped.z;
  return flipped;
}

int main() {
  Point3D p = { 11.3, 4.5, 2.9 };
  Point3D pReflected = reflectXYPlane (p);
  printPoint3D (pReflected);
}

• (11.3, 4.5, 2.9)

• Take a closer look at the implementation of reflectXYPlane.

• (11.3, 4.5, -2.9)

• The point is reflected across the XY plane, so the z value is inverted.

• (-11.3, -4.5, 2.9)

• Take a closer look at the implementation of reflectXYPlane.

• (5.65, 2.25, 1.45)

• Take a closer look at the implementation of reflectXYPlane.

Q-10: What is the output of the code below?

struct Point3D {
  double x, y, z;
};

void printPoint3D (const Point3D& p) {
  cout << "(" << p.x << ", " << p.y << ", " << p.z << ")" << endl;
}

void midpoint (const Point3D& p1, const Point3D& p2, Point3D& p3) {
  p3.x = (p1.x + p2.x) / 2;
  p3.y = (p1.y + p2.y) / 2;
  p3.z = (p1.z + p2.z) / 2;
}

Point3D reflectXYPlane(const Point3D& p) {
  Point3D flipped = p;
  flipped.z = -flipped.z;
  return flipped;
}

int main() {
  Point3D p1 = { 7.0, 3.5, 6.7 };
  Point3D p2 = { 2.0, 1.0, 0.0 };
  Point3D p3 = { 3.9, 4.5, 10.0 };
  Point3D p4 = reflectXYPlane (p1);
  midpoint (p4, p3, p2);
  printPoint3D (p2);
}

• (5.45, 4, 1.65)

• Take a closer look at the implementation of reflectXYPlane.

• (5.45, 4, 8.35)

• Check the arguments passed into midpoint.

• (7.0, 3.5, -6.7)

• Take a closer look at which point is being printed.

• (4.5, 2.25, 3.35)

• Check the arguments passed into midpoint.

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