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?

• Melon: 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?

Answer 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.

• Griffin Wong: But in the next lines of code, can't c change to become more than 0?
• Ketil Tveiten: 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: 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?