8.13. Multiple Choice Exercises¶

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

struct Student {
  string firstName, lastName;
  int year;
  double gpa;
};

struct Professor {
  string firstName, lastName;
  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 studentPop = 3400;
  double avgGPA = 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.
studentPop
An int is not a compound value.
avgGPA
A double is not a compound value.

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

struct Chicken {
  string name;
  int numLegs;
  int 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.
A struct cannot have two instance variables of both string and int
Instance variables of different types in a single struct is fine.
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 numLegs of the Dog object?

struct Dog {
  string name;
  int numLegs;
  bool isPanting;
};

int main() {
  Dog doug = { "Doug", 0, true };
}

Dog.numLegs = 4;
The Dog object is doug. We can use the dot notation on an object.
doug.legs = 4;
Check the name of the instance variable in the struct definition.
doug[legs] = 4;
We can assign values to the instance variables of a struct using dot notation.
doug.numLegs = 4;
Using dot notation on doug, we can set the value of numLegs 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.mass << ", " << c.volume << ", ";
  int density = c.mass / c.volume;
  cout << density;
}

4, 64, 128, 2
Check the ordering of the output statements.
4, 128, 64
Take a closer look at the output statements.
4, 128, 64, 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;
  c = (Cube){ 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.coffeeCupFull when the code is done running?

struct Student {
  string name;
  bool isSleepy;
  bool coffeeCupFull;
};

void pourCoffee (Student s) {
  s.coffeeCupFull = true;
}

int main() {
  Student s = { "Thor Odinson", true, false };
  if (s.isSleepy) {
    pourCoffee (s);
  }
}

true
C++ outputs boolean values as either a 0 or 1.
false
C++ outputs boolean values as either a 0 or 1.
1
Take a closer look at the function definition of pourCoffee.
0
Since we pass a Student object by value to pourCoffee, 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!

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.

Q-11: If the user inputted the string “Darth Vader”, what is the output of the code below?

int main() {
  string quote;
  getline (cin, quote);
  cout << quote << " is the epitome of Star Wars!";
}

quote is the epitome of Star Wars!
quote is not in quotes so the value stored in quote will be printed.
Darth Vader is the epitome of Star Wars!
getline reads the entire line until the user hits Return or Enter.
Darth is the epitome of Star Wars!
Check the manner in which the user input is acquired.
D is the epitome of Star Wars!
Try Again! Pay attention to the way in which user input is recieved.