While Loops + Functions Questions

Questions

Conceptual

  1. What happens if the condition of a while loop is initially False?
  1. The loop will run once.
  2. The loop will not run at all.
  3. The loop will run infinitely.
  4. The loop will throw an error.
  1. If a while loop statement starts with, while condition:, what must condition evaluate to for the following while loop to execute at least once? What type is condition?

SHOW SOLUTIONS

    1. The loop will not run at all.
  2. condition must be True to enter the loop. Its type is a boolean.

 

Diagram

  1. Produce a memory diagram for the following code snippet, being sure to include its stack and output.
    def main() -> None:
        """Main Function"""
        y: int = g(1)
        f(y)
        print(g(f(3)))
        
    def f(x: int) -> int:
        """Function 0"""
        if x % 2 == 0:
            print(str(x) + " is even")
        else:
            x += 1
        return x
        
    def g(x: int) -> int:
        """Function 1"""
        while x % 2 == 1:
            x += 1
        return x

    main()

1.1 Why is it that main() is defined above f() and g(), but we are able to call f() and g() inside main() without errors?

1.2 On line 5, when print(g(f(3))) is called, is the code block inside of the while loop ever entered? Why or why not?

1.3 What would happen if a line was added to the end of the snippet that said print(x). Why?

SHOW SOLUTIONS

The memory diagram includes a box on the top labeled Output and a box on the bottom labeled Stack, next to an area labeled Heap. The first frame in the Stack is labeled Globals and contains the variables main, f, and g. The variable main points to a small box on the heap that says fn 1-5. The variable f points to a small box on the heap that says fn 7-13. The variable g points to a small box on the heap that says fn 15-19. The next frame on the stack is labeled main and contains a return address and a variable y. The return address is 21 and y has a value of 2. The next frame is labeled g and contains a return address, return value, and a variable x. The return address is 2, the variable x has a value of 2 with the previous value of 1 crossed out, and the return value is 3. The next frame is labeled f and contains a return address, return value, and a variable x. The return address is 4, the variable x has a value of 2, and the return value is 2. The next frame is labeled f and contains a return address, return value, and a variable x. The return address is 5, the variable x has a value of 4 with the previous value of 3 crossed out, and the return value is 4. The final frame is labeled g and contains a return address, return value, and the variable x. The return address is 5, the variable x has a value of 4, and the return value is 4. The output box contains a line that says (in quotes) 2 is even. Then, on the next line it says (in quotes) 4.

1.1 Even though main is defined before f and g, it isn’t called until after f and g are defined.

1.2 No because x = 4, so x % 2 == 1 is False, and therefore the code block inside is never run.

1.3 There would be an error because x is a local variable inside both f and g. Therefore, the program does not recognize that x exists in this context.

 

Contributor(s): Alyssa Lytle, Megan Zhang, David Karash