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#1
July 5th, 2013, 07:34 AM
 Avichal
Contributing User

Join Date: Dec 2012
Posts: 69
Time spent in forums: 8 h 21 m 31 sec
Reputation Power: 2
Why is this running infinte times?

Code:
```int main ()
{
int i, n;

for (n = 2; n <= 2; n++)
{
for (i = 2; i <= n; i++)
while (n % i == 0)
{
printf ("%d\n", i);
n /= i;
}
}
}```

This simple loop is running infinitely. I've been debugging for hours now and cannot find a mistake. It must be a simple error but I'm fed up.

#2
July 5th, 2013, 08:01 AM
 noobie1000
Contributing User

Join Date: May 2013
Location: /dev/null
Posts: 146
Time spent in forums: 1 Day 10 h 51 m 6 sec
Reputation Power: 18
Let's trace through what's happening:

1. First n = 2; it goes inside the outermost for-loop
2. Then i = 2; it goes inside the next inner for-loop
3. Now, n % i = 2 % 2 = 0; it goes inside the innermost while-loop
4. Prints i
5. Calculates n = n / i = 2 / 2 = 1. Now n = 1.
6. Next iteration in while loop: n % i = 1 % 2 = 1 != 0; thus control comes out of while loop and into the inner for-loop.
7. i++ = 2 + 1 = 3. Condition is checked: i<=n => 3<=2 => NO; so control comes out of the inner for-loop and into the outermost for-loop.
8. n++ = 1 + 1 = 2 (remember, we did n = n / i in the while loop). Condition is checked: n<=2 => YES; now you're in step #1.

And hence infinite loop.

#3
July 5th, 2013, 08:09 AM
 Avichal
Contributing User

Join Date: Dec 2012
Posts: 69
Time spent in forums: 8 h 21 m 31 sec
Reputation Power: 2
Thank You! Seriously I needed some help, even though it was simple sometimes you just need a fresh mind.

 Viewing: Dev Shed Forums > Programming Languages > C Programming > Why is this running infinte times?

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