silly question FOR LOOP

[bschriek]

I have some silly questions and hopefully an experts can give me a short answer.


1)
For (i=10; i>=0; --i)
{
printf("%u",i); // Result is 10,9,8,7,6,5,4,3,2,1 So far so good.
}
- Why use "i>=0" for expr2 of the FOR LOOP and not "i>0"?

- Sometimes I see "--i" for expr3 of the FOR LOOP and sometimes i--, what's the difference?



2)
For (i=10; i>=0; --i)
{
printf("%u",i); // Now I want the following results 10,9,8,7,6,5,4,3,2,1,0
// (ofcourse i>=0 doesn't work here, but what will work?)
}

Is there a simple solution to use the FOR LOOP without additional code?


As I told you before, stupid questions but I'm just curious.
Thanks you in advance,

[Ttelmah]

The point about --i versus i--, is that in the first case the decrement is done
_before_ the value is passed. In the second afterwards. This matters when
a value decremented like this is being used in mathematics, but not here.

So:
With i=10;

j=i--;

j receives 10, and i is 9 after the operation.

But:

j=--i;

j receives 9, and again i is 9 afterwards.

In the loop, the test is done on the result of the operation, so it makes
no difference.

Now there is a huge caveat in what you post here. It will not work if 'i' is
not a signed variable. An unsigned number can never go less than 0.
You are printing the variable as an unsigned, while the actual value needs
to be a signed to work.

So:

[temtronic]

ok, I was never taught C but...
..my understanding....

1) When the PIC decrements the variable 'i' from '1', it could become 00 or FF ,depending on when the 'if' statement is executed ( kind of a 'race' condition ? ) and HOW it's done. Actually have to see the assembler. for '0' you could check the ZERO flag after the comparison is done.

2) --i means to subtract from i BEFORE the interior for-loop code is executed, and i-- means subtract AFTER...that stuff is executed. One way you get 1 extra for..loop....well ,pretty sure..

What I am sure of is someone will reply and tell us !

[bschriek]

Dear all,

Hihi, oh it's that simple.
I never thought about using a signed int but you are right. Thanks.

And about --i or i--. I understand there is no difference in case of a FOR LOOP.

Thank you for your clear answer.

Best regards,