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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 5.14 Multiple Choice Exercises

1.

What should be the return type of the function convertToCelsius?
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______ convertToCelsius(double fahrenheit) {
  double celsius;
  celsius = (fahrenheit - 32) * 5 / 9;
  return celsius;
}
  • int
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  • What variable are we returning in the function, and what is the variable’s type?
  • double
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  • The function returns celsius, which is a double.
  • string
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  • What variable are we returning in the function, and what is the variable’s type?
  • void
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  • Since we are returning something in the function, the function is not void.
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2.

What would be returned by secretFunction if the input was 14?
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int secretFunction(int input) {
  if (input % 2 == 0) {
    return 3 * input - 2;
  }
  else {
    if (input % 7 == 0) {
      return input;
    }
    return 2 * input + 9;
  }
  return input + 4;
}
  • 14
    🔗
  • Although 14 is divisible by 7, take another look at the conditionals.
  • 18
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  • The flow of code would never reach the last return statement.
  • 36
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  • Check your order of operations!
  • 37
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  • Take a closer look at the conditional statements.
  • 40
    🔗
  • Since 14 is divisible by 2, the function returns two less than three times 14.
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3.

If we wanted to create a boolean function called isPrime, which takes an int input as a parameter, which of the following would be the correct function header?
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  • boolean isPrime(int input) {
    🔗
  • In C++, use the bool keyword for a boolean.
  • bool isPrime (input) {
    🔗
  • In a function header, the type of each variable must be specified in the parameter list.
  • bool isPrime(int input) {
    🔗
  • This is the correct function header for the function.
  • int isPrime(bool input) {
    🔗
  • Take a closer look at what the return type is.
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4.

If we wrote the following function, which of the other functions below can we also legally write and add to the program?
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int func(double x, bool y);
  • int func(double a, bool b);
    🔗
  • Since this function has the same name and parameter types as the given function, it is not allowed.
  • int foo(double x, bool y);
    🔗
  • This function has a different name from the given function, so it is allowed.
  • int func(double x);
    🔗
  • Although this function has the same name as the given function, it has a different number of parameters, so it is allowed.
  • void func(double x, bool y);
    🔗
  • Although this function has a different return type, its parameter list is the same as the given function, so it is not allowed.
  • int func(bool y, double x);
    🔗
  • Although this function has the same name as the given function, its parameter list is in a different order, so it is allowed.
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5.

What is the output of the code below?
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int main() {
  bool x = 2 < 3;
  cout << x;
  cout << false;
  cout << ((1 + 4) * 4 > 24);
  cout << (23 == (32 + 2 - 11));
}
  • 1001
    🔗
  • Since the first and last statements are true and the middle two are false, this is the correct output.
  • truefalsefalsetrue
    🔗
  • In C++, boolean values are outputted as 0 or 1.
  • 1false01
    🔗
  • Since the second cout statement doesn’t have quotes around the word “false”, the value of 0 is outputted.
  • 0110
    🔗
  • Remember that if a boolean expression is true, it has a value of 1.
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6.

What is the output of the code below?
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int main() {
  bool w = !(2 * 3 == 6 || 4 - 3 > 8);
  bool x = true || 4 > 6;
  bool y = 3 != 6 - 3 && 23 >= 23;
  bool z = (4 + 9 < 15 && 3 != 4) || 2 + 5 == 7;
  cout << w << x << y << z;
}
  • 0101
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  • Since the expressions are false, true, false, and true, the output is 0101.
  • 1010
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  • Remember that true outputs to 1 and false outputs to 0.
  • 1101
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  • Remember the NOT operator (!) inverts the value of a boolean.
  • 0100
    🔗
  • Take a closer look at the order of operations.
  • 0110
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  • Take a closer look at the expressions.
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7.

Are there any issues with the code below?
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bool isEven(int num) {
  if (num % 2 == 0) {
    return true;
  }
}
  • Yes, we have to return either 0 or 1.
    🔗
  • Returning a 0 or 1 would be returning an int, even though booleans evaluate to 0 or 1.
  • Yes, we cannot pass an int into a bool function.
    🔗
  • The type of variables in the parameter list do not affect the return type.
  • Yes, there is no case for odd numbers.
    🔗
  • Since we never established an else clause, if the input was an odd number, the function would not return anything despite not being a void function.
  • There are no issues with the code.
    🔗
  • There is an issue with the code. Can you find it?
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8.

Are there any issues with the code below?
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double Free_time(int day) {
  if (day == 1 || day == 2 || day == 3 || day == 4) {
    cout << "Better study on weekday!" << endl;
    return day*0.25;
  }
  else{
    cout << "Happy weekend" << endl;
    return day;
  }
}
  • Yes, we might not return anything.
    🔗
  • We have an else clause in which we return a value.
  • Yes, we cannot return an entire expression like day*0.25.
    🔗
  • If the result of the expression is compatible with the return type we can return it.
  • Yes, we are returning an int (in the else block) where as the return type is double .
    🔗
  • Implicit conversion from an int to double is ok in c++!
  • There are no issues with the code.
    🔗
  • Correct! implicit conversion from int to double are ok!
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9.

Are there any issues with the code below?
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void moonWeight(double earth) {
  double moon = 0.165 * earth;
  cout << "You would weigh " << moon << " pounds on the moon." << endl;
  return moon;
}
  • Yes, we cannot have cout statements in a function.
    🔗
  • We are allowed to use cout statements in a function.
  • Yes, we cannot return anything.
    🔗
  • void functions do not have return values, so we cannot return moon.
  • Yes, we need to return the output statement.
    🔗
  • void functions do not have return values.
  • There are no issues with the code.
    🔗
  • There is an issue with the code. Can you find it?
🔗

10.

What is the return type of main?
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  • void
    🔗
  • What keyword do we use before main() in every program?
  • bool
    🔗
  • What keyword do we use before main() in every program?
  • double
    🔗
  • What keyword do we use before main() in every program?
  • int
    🔗
  • Yes, main is supposed to return an integer, which is why programmers often return 0 at the end of main.
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11.

What is the base case of the factorial recursive function?
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int factorial(int n) {
  if (n == 0) {
    return 1;
  }
  else {
    int recurse = factorial(n-1);
    int result = n * recurse;
    return result;
  }
}
  • n = 0
    🔗
  • When n is 0, the function returns the value 1 without making a recursive call.
  • n = 1
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  • When n is 1, the function makes a recursive call in the else statement.
  • n = -1
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  • n never becomes -1.
  • There is no base case.
    🔗
  • If there was no base case, the function would recurse infinitely.
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12.

What is printed?
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void print_sequence(int n) {
  if (n == 0) {
     cout << 1;
     return;
     //we can have an empty return to a void function
  }
  else {
    cout << n << " ";
    print_sequence(n - 1);
  }
}

int main() {
    int val=6;
    print_sequence(val);
}
  • 6 5 4 3 2 1 0
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  • Check what the base case prints.
  • 6 6 6 6 6 6 1
    🔗
  • What value do we give the recursive call?
  • 6 5 4 3 2 1
    🔗
  • The base case prints something!
  • 6 5 4 3 2 1 1
    🔗
  • We print a number and decrement it till we reach 0 then we print 1.
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