Problems with while loops in Python

Question

I'm doing a project Euler question (if you've done it, don't spoil it!) I've create a while loop in the following code. When I run the code, it doesn't give me an error message, but just doesn't give me an answer. I suspect that there is a problem with my while loop that makes it loop on infinitely.

import math
def euler(n):
    m=[]
    a=1
    c=0
    while c<=int(n):
        a+=a
        c=0
        for x in range(1, int(math.sqrt(a))+1):
            if n%x==0:
                if n/x==x:
                    c+=1
                else:
                    c+=2
    print(a)

I don't know what's wrong with the loop. Could someone help me understand what is wrong and why?

Did you try to run this code with a debugger and see what happens to values: c, n, a, x? Also, what do you need m=[] for? I don't see it being used anywhere in the code? — Melon
– Melon, Commented Jan 11, 2019 at 7:51

Mayank Porwal · Accepted Answer · 2019-01-11 06:58:58Z

1

The problem is the c=0 statement inside the while loop.

while c<=int(n):
        a+=a
        c=0  ## Problematic
        for x in range(1, int(math.sqrt(a))+1):
            if n%x==0:
                if n/x==x:
                    c+=1
                else:
                    c+=2

For every iteration c is becoming 0 in the while loop, so it will always be less than n. Hence the loop runs infinitely.

answered Jan 11, 2019 at 6:58

Mayank Porwal

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3 Comments

Griffin Wong Over a year ago

But in the next lines of code, can't c change to become more than 0?

Ketil Tveiten Over a year ago

You're incrementing c at most by 2 for each factor of n, and you'd have to be lucky for that to add up to n or more.

Griffin Wong Over a year ago

Why does it run on infinitely though? Even if I type a number like 5, the code runs infinitely. Why are the c+=1s and c+=2s not working?

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