5.13. Multiple Choice Exercises

Q-1: What is the output of the code below?

int main() {
  int x = 0;
  int i = 1;
  while (i < 10) {
    x = i;
    i++;
  }
  cout << x;
}

• 0

• x is initialized to 0, but it’s value is reassigned in the while loop. Can you figure out what the final value assigned to x is?

• 1

• When i is 1, x is assigned the value of i, so x is 1. However, the while loop continuously increments i, so the final value of x is not 1.

• 9

• x is assigned the value of 9 during the last iteration of the while loop, and thus 9 is the output of the program.

• 10

• i is incremented to a value of 10, but since i < 10 is false, the contents of the while loop is not executed, so x is never assigned the value of 10.

Q-2: What is the final value of i when the code is finished running?

int main() {
  int x = 0;
  int i = 1;
  while (i < 10) {
    x = i;
    i++;
  }
  cout << x;
}

• 0

• i is initialized with a value of 1 and is incremented, so it will never have a value of 0.

• 1

• i is initialized with a value of 1 but it is incremented during the while loop.

• 9

• This is the final value of x when the code is finished running.

• 10

• In order for the while loop to terminate, the condition i < 10 must be false, and this is achieved when i is incremented to 10.

Q-3: How many times does the following while loop run?

int main() {
  int i = 6;
  while (i > 2) {
    i = i + 4;
    if (i > 8) {
      i = i - 5;
    }
  }
}

• 1

• Take a closer look at the while loop and conditional.

• 3

• Take a closer look at the while loop and conditional.

• 5

• Take a closer look at the while loop and conditional.

• The loop will run infinitely.

• The value of i will always be greater than 2, resulting in an infinite loop.

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

int main() {
  int n = 10;
  // cout << "Da ";
  cout << "na ";
  while (n != 3) {
    cout << "na ";
    n--;
  }
  cout << "Batman!";
}

• na na na na na na na na Batman!

• The code prints out eight “na”s before printing out “Batman!”

• na na na na na na na Batman!

• Look over the code carefully. There are output statements before the while loop.

• Da na na na na na na na na Batman!

• Will “Da” ever be printed?

• It will result in an infinite loop.

• Since we repeatedly decrement n inside the while loop, it will eventually be equal to 3 and the while loop will terminate.

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

int main() {
  int n = 10;
  cout << "Da ";
  cout << "na ";
  while (n != 3) {
    cout << "na ";
  }
  cout << "Batman!";
}

• Batman!

• Take a closer look at the while loop.

• Da Batman!

• Take a closer look at the while loop.

• Da na na na na na na na na Batman!

• Take a closer look at the while loop.

• It will result in an infinite loop.

• Since we never change the value of n, 10 will never equal 3 so the code will run forever.

Q-6: What is the output of the code below?

int main() {
  int x = 1;
  while (x < 6) {
    cout << x << "\t" << pow (x, 5) / pow (x, 3) << endl;
    x++;
  }
}

• The first six perfect fifths.

• Take a closer look at the while loop and what x was initialized to.

• The first six perfect squares.

• Take a closer look at the while loop and what x was initialized to.

• The first five perfect squares.

• Dividing x to the power of 5 by x to the power of 3 effectively results in perfect squares.

• The first five perfect cubes.

• Take a closer look at the mathematical expression inside the while loop.

Q-7: Why are we allowed to use the variable x in both main and in the function definition of superSecretFunction?

int superSecretFunction (int n) {
  int x = 0;
  return (2 + (n * n) - 5 * n / 7) * x;
}

int main() {
  int x = 1;
  cout << "After using the super secret function, we get " << superSecretFunction (x);
}

• We’re using the same variable, but just reassigning the value from 0 to 1.

• We are actually using two different variables that happen to have the same name.

• Although the name of both variables is x, they represent different locations in memory, and thus are different variables.

• One x is a local variable of superSecretFunction while the other is a local variable of main.

• We can assign them different values but not the same value. Thus, if both were initialized to 0, then we’d get an error.

• Since they are not in the same storage location, they can store any value, including the same value.

• We’re not allowed to do this. The code will result in an error.

• The code does not produce an error.

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

int loopFive (int n) {
  while (n % 5 != 0) {
    n = n + 3;
  }
  return n;
}

int main() {
  cout << loopFive (2);
  cout << loopFive (3);
  cout << loopFive (4);
}

• 51510

• n is repeatedly incremented by 3 until it is divisible by 5, and this happens when n is 5, 15, and 10 for the inputs of 2, 3, and 4 respectively.

• 234

• Although the function returns n, n might not be its original value.

• 5 15 10

• Take a closer look at the output statements.

• 567

• Take a closer look at the while loop in the function.

Q-9: The super evil villian RePete wants to annoy the city by hacking into the city’s helper robots and making them repeat everything they say 5 times. However, there’s an error in his code and now the robots won’t stop repeating! Can you find the error?

void repeat_bot (string input) {
  int n = 0;
  while (n < 5) {
    cout << input << ' ';
    n--;
  }
}

int main() {
  repeat_bot ("Hello, how may I help you?");
}

• repeat_bot can only take one word as an argument.

• A string is any number of characters or words surrounded by double quotes, not just one word.

• n is declared to be 0 and 0 is always less than 5.

• The code doesn’t loop infinitely because of the value n was declared to be.

• Every time the while loop runs, n is reset to 0, so it will always be less than 5.

• The initialization of n occurs outside the while loop, so the value of n does not get reset to 0.

• n is declared to be 0 and we continuously decrement n so it will always be less than 5.

• Since n starts at 0 and gets smaller, the conditional for the while loop will always be true, and thus the code runs forever.

Q-10: After making some changes to his code, RePete tries again. This time, however, the robots don’t repeat anything! Can you find the new error?

void repeat_bot (string input) {
  int n = 0;
  while (n > 5) {
    cout << input << ' ';
    n++;
  }
}

int main() {
  repeat_bot ("Hello, how may I help you?");
}

• n > 5 is not a valid conditional, so the while loop doesn’t execute.

• n > 5 is a boolean statement and thus is a valid conditional.

• The value of n never gets modified in the while loop.

• n is incremented in the while loop after the cout statement.

• In the cout statement, only spaces are printed.

• input is also printed.

• The conditional for the while loop is not met.

• Since n is declared to be 0, 0 is not greater than 5, so the while loop does not execute.

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