8.13. Multiple Choice Exercises

Q-1: Which of the following are compound values?

struct student {
  string first_name, last_name;
  int year;
  double gpa;
};

struct professor {
  string first_name, last_name;
  string department;
  int class;
};

int main() {
  student x = { "John", "Doe", 2, 3.46 };
  student y = { "Jane", "Doe", 3, 3.68 };
  professor z = { "Richard", "Roe", "Computer Science", 101 };
  string college = "University of College";
  int student_pop = 3400;
  double avg_gpa = 3.2;
}

• x

• x is a student which is a struct.

• y

• y is a student which is a struct.

• z

• z is a professor which is a struct.

• college

• college is a string which is made up of characters.

• student_pop

• An int is not a compound value.

• avg_gpa

• A double is not a compound value.

Q-2: What is wrong with the following struct definition?

struct chicken {
  string name;
  int num_legs;
  int eggs;
  bool eggs;
}

• The word “struct” needs to be capitalized.

• “struct” shouldn’t be capitalized in a struct definition.

• There needs to be a semicolon after the end curly brace.

• It is a common error to forgot the semicolon at the end of struct definitions.

• The struct cannot have two instance variables that are both named eggs.

• Two symbol names in the same scope is a compile error

• There is nothing wrong with the struct definition.

• There is an error with the definition. Can you find it?

Q-3: How do we assign the value of 4 to the instance variable num_legs of the dog object?

 struct dog {
   string name;
   int num_legs;
   bool is_panting;
 };

int main() {
  dog fido = { "Fido", 0, true };
}

• dog.num_legs = 4;

• The dog object is fido. We can use the dot notation on an object.

• fido.legs = 4;

• Check the name of the instance variable in the struct definition.

• fido[legs] = 4;

• We assign values to the instance variables of a struct using dot notation.

• fido.num_legs = 4;

• Using the member access operator on fido, we can set the value of num_legs to 4.

Q-4: What is the output of the code below?

struct Cube {
  int edgeLength;
  int volume;
  int mass;
};

int main() {
  Cube c;
  c.edgeLength = 4;
  c.volume = 64;
  c.mass = 128;
  cout << c.edgeLength << ", " << c.volume << ", " << c.mass << ", ";
  int density = c.mass / c.volume;
  cout << density;
}

• 4, 2, 64, 128

• Check the ordering of the output statements.

• 4, 64, 128

• Take a closer look at the output statements.

• 4, 64, 128, 2

• The code outputs all instance variables and the density in the proper order.

• edgeLength, volume, mass, density

• Dot notation accesses the values of the instance variables, not the names.

Q-5: What is the output of the code below?

struct Cube {
  int edgeLength;
  int volume;
  int mass;
};

int calculateDensity (Cube c) {
  return c.mass / c.volume;
}

int main() {
  Cube c = { 2, 8, 4 };
  int density = calculateDensity (c);
  cout << density;
}

• 0

• Because of integer division, density is 0 and thus the output is 0.

• 2

• Density is mass divided by volume.

• 0.5

• Take a closer look at what kind of division we are doing.

• 1

• Integer division truncates the extra digits.

Q-6: What is the value of s.coffee_cup_full when the code is done running?

struct student {
  string name;
  bool is_sleepy;
  bool coffee_cup_full;
};

void pour_coffee (student s) {
  s.coffee_cup_full = true;
}

int main() {
  student s = { "Thor Odinson", true, false };
  if (s.is_sleepy) {
    pour_coffee (s);
  }
}

• true

• Take a closer look at the function definition of pour_coffee.

• false

• Since we pass a student object by value to pour_coffee, the function makes a copy of the object and does not modify the original. If you wanted the original value to change, pass it by reference!

• 1

• The type of coffe_cup_full is bool.

• 0

• The type of coffe_cup_full is bool.

Q-7: What is the value of r.batteryLevelPercentage when the code is done running?

struct Robot {
  string name;
  int batteryLevelPercentage;
  bool isFullyCharged;
};

void chargeRobot (Robot& r) {
  if (r.batteryLevelPercentage + 50 > 100) {
    r.batteryLevelPercentage = 100;
    r.isFullyCharged = true;
  }
  else {
    r.batteryLevelPercentage = r.batteryLevelPercentage + 50;
  }
}

int main() {
  Robot r = { "Rob", 60, false };
  chargeRobot (r);
}

• 100

• The Robot object is passed by reference to chargeRobot, which caps the batteryLevelPercentage at 100.

• 110

• Take a closer look at the chargeRobot function.

• 60

• Is the Robot object passed by value or by reference to chargeRobot?

• 1

• That is the final value of r.isFullyCharged.

Q-8: What is the output of the code below?

void foo (int& x, int y) {
  x = x + 4;
  y = 2 * x + 3 * y;
}

void bar (int x, int y) {
  y = 2 * x;
  x = x - 1;
  foo (x, x);
}

void func (int &x, int& y) {
  x = x + 3;
  bar (y, x);
}

int main() {
  int x = 4;
  int y = 7;
  func (y, x);
  cout << x << ", " << y;
}

• 4, 7

• Take a closer look at func and its parameters. Are they passed by value, passed by reference, or both?

• 4, 10

• Since bar doesn’t pass either parameter by reference, neither bar nor foo affect the values of x and y.

• 7, 7

• Check the order of the arguments passed into func.

• 35, 8

• Take a closer look at the three functions. Are they all passed by reference?

Q-9: If the user inputted the string “R2-D2”, what is the output of the code below?

int main() {
  string name;
  cin >> name;
  cout << "Hello, " << name << "!";
}

• R2-D2

• Take another look at the cout statement.

• Hello name!

• name is not in quotes so the value stored in name will be printed.

• Hello, R2-D2!

• “R2-D2” is stored in name and is then outputted in the cout statement.

• name

• cin reads input from the user.

Q-10: If the user inputted the string “C-3PO”, what is the output of the code below?

int main() {
  char name;
  cin >> name;
  cout << "Hello, " << name << "!";
}

• Hello, CPO!

• cin reads the first char in from user input.

• Hello, C!

• Since ‘C’ is the first char in the input, this is the correct output. The program will ignore everything that comes after the first char.

• Hello, C-3PO!

• Check the data type of name.

• Error, we cannot read a character from user input.

• We can read characters from user input.

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