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How To Think Like a Computer Scientist C++ Edition The Pretext Interactive Version

Barbara Ericson, Allen B. Downey, Jason L. Wright (Editor)

Exercises 12.12 Multiple Choice Exercises

1.

Select all of the true statements.
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  • You can have a vector that stores a vector of objects.
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  • C++ allows for a variety of different compositions.
  • In order to check to see if two Cards are equal, we can use the == operator.
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  • We have to write a function that compares two Cards.
  • There is no faster way to search through an unsorted vector than using a linear search.
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  • If the vector were sorted, then there are faster search methods.
  • There is no such thing as an empty object.
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  • All variables are given default values unless otherwise specified by the user.
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2.

What is the correct way to declare a vector of vectors of ints called vec?
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  • vector<int> vec;
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  • This declares a vector of ints.
  • vector<int> vec<int>;
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  • This is not the proper way to declare vec.
  • vector<vector<int> vec;
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  • Close! Look closely at the answer choices again.
  • vector<vector<int> > vec;
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  • This is the proper way to declare a vector of vectors of ints.
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3.

What is the value of card?
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struct Card {
  int suit, rank;
  Card();
  Card(int s, int r);
};

Card::Card() {
  suit = 0;  rank = 0;
}

Card::Card(int s, int r) {
  suit = s;  rank = r;
}

int main() {
  Card card (2, 8);
}
  • Ace of Clubs
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  • How did we define our mapping earlier in the chapter?
  • 8 of Hearts
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  • card has a suit value of 2 corresponding to Hearts, and a rank value of 8.
  • King of Hearts
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  • How did we define our mapping earlier in the chapter?
  • card does not have a value.
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  • We initialized card with a suit value of 2 and a rank value of 8.
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4.

There is an error with the code below. Can you find it?
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struct Card {
  int suit, rank;
  Card();
  Card(int s, int r);
  void print() const;
};

int main() {
  Card card (1,3);
  print (card);
}
  • card is not a valid Card.
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  • A suit of 1 and a rank of 3 maps to the 3 of Diamonds.
  • There shouldn’t be a semicolon after the struct definition.
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  • A struct definition always ends with a semicolon.
  • print is a member function.
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  • Since print is a member function, we need to use the dot operator.
  • There is nothing wrong with the code.
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  • There is an error with the code. Can you find it?
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5.

What is the output of the code below?
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struct Card {
  int suit, rank;
  Card();
  Card(int s, int r);
  void print() const;
  bool isGreater(const Card& c2) const;
};

int main() {
  Card card1 (2,12);
  Card card2 (2,2);
  cout << card1.isGreater (card2) << endl;
}
  • True
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  • The output of a bool is either a 0 or 1.
  • False
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  • The output of a bool is either a 0 or 1.
  • Is card1 greater than card2?
  • The Queen of Hearts is greater than the 2 of Hearts.
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6.

What is the output of the code below?
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struct Card {
  int suit, rank;
  Card();
  Card(int s, int r);
  void print() const;
  bool isGreater(const Card& c2) const;
};

vector<Card> buildDeck();

bool equals(const Card& c1, const Card& c2) {
  return (c1.rank == c2.rank && c1.suit == c2.suit);
}

void printDeck(const vector<Card>& deck);

int find(const Card& card, const vector<Card>& deck);

int main() {
  vector<Card> deck = buildDeck();
  Card card (3, 13);
  cout << find(card, deck);
}
  • 51
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  • The card is the King of Spades, which is located at the end of the deck.
  • 52
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  • Since the vector is size 52, it cannot have an index of 52.
  • 12
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  • What is the value of card?
  • -1
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  • What is the value of card?
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7.

What is true about deck?
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struct Card {
  int suit, rank;
  Card();
  Card(int s, int r);
  void print() const;
  bool isGreater(const Card& c2) const;
};

vector<Card> createDeck() {
  vector<Card> deck(12);
  int i = 0;
  for (int suit = 0; suit <= 3; suit++) {
    for (int rank = 1; rank < 4; rank++) {
      deck[i].suit = suit;
      deck[i].rank = rank;
      i++;
    }
  }
  return deck;
}

int main() {
  vector<Card> deck = createDeck();
}
  • It contains 12 Cards.
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  • createDeck returns a vector of size 12, corresponding to 12 Cards.
  • The highest rank is 4.
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  • The rank goes up to but does not include 4.
  • There are no spades in the deck.
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  • The suit goes up to and include the suit value 3 which corresponds to spades.
  • The deck has 3 cards in each suit.
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  • Each suit has an Ace, 2, and 3.
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8.

How many times does findBisect need to call itself in order to find the King of Diamonds?
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struct Card {
  int suit, rank;
  Card();
  Card(int s, int r);
  void print() const;
  bool isGreater(const Card& c2) const;
};

vector<Card> buildDeck();
bool equals(const Card& c1, const Card& c2);
void printDeck(const vector<Card>& deck);
int find(const Card& card, const vector<Card>& deck);
int findBisect(const Card& card, const vector<Card>& deck, int low, int high);

int main() {
  vector<Card> deck = buildDeck();
  Card card (1, 13);
  cout << findBisect(card, deck, 0, 51);
}
  • The King of Diamonds is right in the middle of the deck, so it doesn’t need to call itself.
  • Where is the King of Diamonds located relative to the sorted deck?
  • Where is the King of Diamonds located relative to the sorted deck?
  • Where is the King of Diamonds located relative to the sorted deck?
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9.

We want to write the function findAllQueens, which searches through a deck and prints out the location of all 4 queens in the deck. What should go in the blanks?
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struct Card {
  int suit, rank;
  Card();
  Card(int s, int r);
  void print() const;
  bool isGreater(const Card& c2) const;
};

vector<Card> buildDeck();
bool equals(const Card& c1, const Card& c2);
void printDeck(const vector<Card>& deck);

void findAllQueens(const vector<Card>& deck) {
  for (size_t i = 0; i < deck.____; ++i) {
    if (deck[i].____ == 12) {
      cout << ____ << " ";
    }
  }
}

int main() {
  vector<Card> deck = buildDeck();
  findAllQueens (deck);
}
  • push_back(), suit, i
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  • What value should i go up to?
  • size(), rank, i
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  • These are the correct variables and functions.
  • size, rank, deck[i]
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  • We want to print the index, not the card.
  • front(), suit, deck
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  • What value should i go up to?
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10.

What is the process of modeling a complex system with a simplified description in order to suppress unnecessary details while capturing relevant behavior?
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  • Generalization
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  • Generalization means to take something specific and make it more general.
  • Encapsulation
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  • Encapsulation means taking a piece of code and wrapping it up in a function.
  • Abstraction
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  • Using this process, we can remove unnecessary details to focus on the more important aspects.
  • Implementation
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  • Implementation is the process of taking an idea and making it real.
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