Why is this an infinite loop!?

[AmbliKai]

Hi while writing a bit more code for a little project i'm doing, (trying to teach myself c)

i wrote this:

#include <stdio.h>

int main()
{
int i, a;

for (i = 0; i <= 8; i++)
{
	for (a = 0; a <= 8; i++)
		printf("i = %d\n", i);

}

}

The output was a little unexpected:

...

i = 10388
i = 10389
i = 10390
i = 10391
i = 10392
i = 10393
i = 10394
i = 10395
i = 10396
i = 10397
i = 10398
i = 10399
i = 10400
i = 10401
i = 10402
i = 10403
i = 10404
i = 10405
i = 10406
i = 10407
i = 10408
i = 10409
i = 10410
i = 10411
i = 10412
i = 10413
i = 10414
i = 10415
i = 10416
i = 10417
i = 10418
i = 10419
i = 10420
i = 10421
i = 10422
i = 10423
i = 10424
i = 10425
i = 10426
i = 10427
i = 10428
i = 10429
...

And so on! I can't understand what i'm doing wrong as i thought the conditions in the for loop would keep it in check. Surely i shouldn't be more than 8? No?

Thanks in advance from a newb!
Simon

[matsp]

for (a = 0; a <= 8; i++)

--
Mats

[sppraveen_c]

Hi

The problem is in the increment part
First time i will be zero and will enter the second for loop .
here the condition is a<8 but a is never incremented in this inner for loop and so it keeps incrementing i and prints them all,but will never go to the outer loop and hence the unexpected result.

Praveen SP

[AmbliKai]

I'm sorry, i don't understand.

i++ ++i and i + 1 all have the same effect.

i understand that i++ increments 'i' but returns the old non incremented value, but i thought that the condition in the for loop would limit the output?

i.e i was under the impression that due to the condition 'i' could never be greater than 8?
regards
Simon.

[AmbliKai]

Ah sorry, didn't see that, i++ should have been a++!

Thanks, feel a bit stupid now!

So whats the difference between i++ and ++i?

Si.

[MacGyver]

So whats the difference between i++ and ++i?

In C, when alone, nothing.

When used as an expression, i++ will return the value of i before it was incremented, while ++i will increment i and used the incremented value in the expression.

Example:

int x = 5;
int y = x++;

y will be 5 and x will be 6.

int x = 5;
int y = ++x;

Both y and x will be 6.

In C++, apparently i++ does some copy stuff, which, if you're using primitive data types (ie. int, char, etc.) then this does not apply/matter. This is only really for objects.

[AmbliKai]

Cool, sounds like a useful bit of knowledge to know!

Thanks everyone.

Si.

[dwks]

In C++, apparently i++ does some copy stuff, which, if you're using primitive data types (ie. int, char, etc.) then this does not apply/matter.

There was a discussion about this, long, long ago: http://cboard.cprogramming.com/showthread.php?t=68136