How do I define condition for while-loop in Python ?

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I already finish the task, just need an explanation. I'm trying to compute the nearest square of a number less than a limit using python. Let's say if my limit is 40, then the nearest square would be 36 (from 6*6).

What I have tried:

I already found the answer, but need some explanation :

limit = 40
num = 0

while (num+1)**2 < limit:
    num += 1
nearest_square = num**2

print(nearest_square)

It works, the output answer is 36. But I'm still a little bit confused about the condition needed. Originally, I put this :

while (num**2) < limit:

But the answer is 49, which means 7*7 and more than the limit. Why does the "+1" needed in the condition ? Is it not like "for" loop ?

Posted 7-Feb-20 9:28am

lock&_lock

Updated 7-Feb-20 10:36am

v3

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Patrice T · Accepted Answer · 2020-02-07T10:23:00

Solution 1

First a typo: "But the answer is 49, which means 7*7"

Quote:
I'm trying to compute the nearest square of a number less than a limit using python.

If limit is 36, which answer do you expect 25 or 36 ?

Quote:
It works, the output answer is 36. But I'm still a little bit confused about the condition needed.

You loop until condition is wrong, and it turn wrong when num is 1 step too far.
You could have done it that way:

Python

limit = 40
num = 0
while num**2 < limit:
    num += 1
nearest_square = (num-1)**2
print(nearest_square)

Posted 7-Feb-20 10:23am

Patrice T

Comments

lock&_lock 7-Feb-20 16:40pm

Thanks for pointing out my typo and giving explanation. If my limit is 36, I'd expect the result = 36, that I believe I can manage. When it's ONE STEP TOO FAR, now I understand how it works, thank you. I'm gonna remember this.

CPallini 7-Feb-20 17:04pm

5.

Patrice T 7-Feb-20 17:13pm

Thank you