Understanding how a break statement functions in zybook question for python 5.10.1

Question

it's a weekend and my professor isn't answering emails, we went over break statements in class and I was sure I understood it, but I keep getting questions like this wrong (it wants you to show the output):

    stop = int(input())
    result = 0
    for a in range(3):
        for b in range(4):
            result += a + b
        print(result)
        if result > stop:
            break

I put this into Pycharm with the input '17' (I had tried so many attempts before to get the answer on my own, but zybooks gives you randomized problems in their challenge activities, and it wasn't giving an explanation that was helpful) because I wanted to try and reverse engineer why the solution was the way it was, the output is:

6
16
30

first of all, I'm not sure why after it breaks it outputs the last number, since there's no print statement for the outer 'for' loop. If I ignore that, the output I'm coming out with is:

6
16
18

I even wrote out how I think the RAM is storing these values and changing them (my professor said this was a good idea to do if you are having trouble since it helps step through the process the computer takes. Included below is a link to the picture of that, I'm sorry if it doesn't make sense. https://imgur.com/a/t5o24Mo

I'm not trying to cheat, this homework is due Sunday, I would email my professor if I could to ask for help.

I tried to manually go through each iteration and figure out what each variable was and how it changed each iteration. I'm getting the first 2 iterations of the outer loop correct, but the break statement is where I'm having a problem.

18 would be the right answer, if the break was inside the for b in range(4): loop. But it's not, so that loop always runs its full four iterations. — John Gordon
– John Gordon, Commented Oct 7, 2023 at 23:22
Ahhh, so the break statement is not executed until the for b in range(4): has finished all of its four iterations, and the for a in range(3): loop begins again, --even if result is already past the limit defined by stop-- because the break statement is for the for a in range(3): loop. Learned I have to pay more attention to how indentations and line placement alter the code's behavior. Thank you so much! — Ben Turner
– Ben Turner, Commented Oct 7, 2023 at 23:31

John Gordon · Accepted Answer · 2023-10-07 23:27:36Z

1

If you're not sure why the code is doing something, one easy way to help you figure it out is to just add more print statements, so you can see the variables at every step of execution.

Something like this:

for a in range(3):
    print("At the top of a range loop, a is:", a)
    for b in range(4):
        print("At the top of b range loop, b is:", b)
        print("a+b is:", a+b)
        print("Before adding, result is:", result)
        result += a + b
        print("After adding, result is now:", result)
    if result > stop:
        print("result", result, "is bigger than stop", stop, "so we will break the loop")
        break
    else:
        print("result", result, "is not bigger than stop", stop, "so the loop will keep going")

edited Oct 7, 2023 at 23:27

answered Oct 7, 2023 at 23:17

John Gordon

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Ben Turner Over a year ago

Brilliant idea I will definitely use going forward that is so helpful.

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