23 Jun
2004
23 Jun
'04
1:38 p.m.
> > > int N = 10;
> > > while (N--) printf("%d\n",N);
> > > What are the first and last numbers displayed?
On Wed, 23 Jun 2004, Sean 'Captain Napalm' Conner wrote:
Precedence rules I can look up. If *I'm* in
doubt, I'll add parentheses
to make my intent clear.
I teach my students to use parentheses VERY liberally
(wheneverthere is ANY possibility of ambiguity or doubt)
but I also teach them that they will have to be able to
understand other people's code that might not have them
in places where they would be useful.
I've been working with C for over ten years and
*I* got it wrong, which I
then you don't agree with Jules that it is too trivial to consider?
But the REAL question is "how much would a book help?"
can understand because the compiler is free to insert
the increment anywhere
between sequence points (I guess I didn't realize there was a sequence point
in the middle there). I thought I used that form, but in going over my
code, it looks like I've actually avoided that particular construct (while
(var--) ... )in my code (heck, I'm looking over 10 year old code and I can't
find that particular form).
I don't care overly much for it, but have seen it quite a bit.
Another example to be wary of:
i = 1;
printf("%d %d %d\n",i++,i++,i++);
I've seen different results from different compilers, all ANSI C
compliant (GCC does what people expect, while the IRIX compiler followed the
letter, if not the spirit, of the standard).
There are SOME things that K&R explicitly say are compiler
dependent or undefined, such as A[N++] = N; (sequence of lvalue v
rvalue evaluation is not defined (at least in original K&R))
In fact,
I'd be willing to bet that 10% of the folks on this
list who claim to know C would get it wrong! And several of
those would argue about the answer without trying it.
(if N were to be declared "unsigned", even more would get it wrong!)
Really? Once you realize that C treats the value of 0 as false, and
anything else as true, then there isn't any difference between using a
signed or unsigned int in the loop (okay, I cheated, I ran the fragment of
code both ways---that's how I know I'm wrong).