23 Jun
2004
23 Jun
'04
1 p.m.
It was thus said that the Great Fred Cisin once stated:
On Wed, 23 Jun 2004, Jules Richardson wrote:
Sure, for somebody who says that they know a language,
coming to you for a job.
But for a student part way through the course (MID-TERM!), it is
a simple test for whether they can apply the order of precedence
rules.
Precedence rules I can look up. If *I'm* in doubt, I'll add parentheses
to make my intent clear.
int N =
10;
while (N--) printf("%d\n",N);
What are the first and last numbers displayed?
is appropriate for open-book.
Hmm, personally I wouldn't want to hire anyone saying they knew a
language if that was typical of the sort of thing they'd been asked in
an exam where they also had the reference material handy! Any student
should be able to say what the result is without having to resort to any
kind of reference. This is NOT an employment exam!
It is from a mid-term exam, one of 50 questions to be done
in 2 hours, intended to find out which students
can APPLY precedence rules (and wake them up!).
VIRTUALLY anybody who has to look it up, will almost certainly
get it wrong, since the book(s) may make it quite clear about
when the decrement is applied relative to the conditional test,
but will NOT tell them about whether the decrement is applied
before or after the BODY of the loop. If they UNDERSTAND,
then they will get it right.
I've been working with C for over ten years and *I* got it wrong, which I
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).
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).
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).
But if we're going to go into gotchas of C, what's wrong with this code?
void foo(char *s)
{
int charcount[256];
memset(charcount,0,sizeof(charcount));
for ( ; *s ; s++)
{
charcount[*s]++;
}
}
-spc (And no, not being Unicode savvy isn't one of the problems I'm
looking for ... )