Exercises 9.13 Multiple Choice Exercises

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.

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.

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;
  mockingbird.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 Mockingbirdby Harper Lee (1960), $7.19
The \ are escape characters. Used in this context, they allow us to print quotation marks.

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.

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?

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.

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.

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.

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.

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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