Function & header files

[Umesh]

LOOKS FINE BUT IF FAILS TO WORK FOR n>12
WHAT ABOUT USING LINKED LISTS?

 

[Keith Thompson]

WHICH COMPILER(S) DO YOU USE?

GCC and other C compilers now support many of the new features of C99.
However, there has been less support from vendors such as Microsoft
and Borland that have mainly focused on C++, since C++ provides
similar functionality improvement.

GCC, despite its extensive C99 support, is still not a completely
compliant implementation; several key features are missing or don't
work correctly

[...]

The above two paragraphs are an uncredited direct quote from a
Wikipedia article,
<http://en.wikipedia.org/wiki/C_(programming_language)>.

There's nothing wrong with quoting from outside sources, and the
quoted material happens to be correct, but failing to provide
attribution is rude and dishonest.

 

[Keith Thompson]

LOOKS FINE BUT IF FAILS TO WORK FOR n>12
WHAT ABOUT USING LINKED LISTS?

[...]

Don't shout. (Writing in all-caps represents shouting.)

Don't top-post. We've explained this to you numerous times; you've
shown no evidence so far of being intelligent enough to understand it,
but we're prepared to be pleasantly surprised.

Be less obnoxious.

 

[Keith Thompson]

"Keith Thompson" <[email protected]> ha scritto nel messaggio

Here's another program that uses a macro to compute factorials:
[code snipped]

The use of a macro is equally gratuitous, but at least this one
operates more usefully. On a system with 32-bit longs, either program
works only for arguments up to 12; using unsigned long rather than
long didn't add enough range to change that. With 64-bit longs, it
works for arguments up to 20. Neither version checks for overflow
(which would be fairly difficult to do)

#include <limits.h>
#include <errno.h>
long factorial(int n)
{
long f = 1;
int i;
if (n < 0) {
errno = EDOM;
return n % 2 ? LONG_MIN : LONG_MAX;
}
for (i = 1; i <= n; i++) {
if (f > LONG_MAX / i) {
errno = ERANGE;
return LONG_MAX
} else
f *= i;
}
errno = 0;
return f;
}
Fairly difficult?

Well, sufficiently difficult than I was unwilling to take the time to
do it.

 

[Keith Thompson]

Until you build it on a system whose int is 512 bit ;-)

If you really need to compute factorials, chances are you'll need them
for arguments that won't fit in any integer type, even if you have
512-bit integers.

 

[Army1987]

(snip code)


Remember, you're callling this via a macro.

#include <errno.h>
#define factorial(n) \
do { \
int n_ = n; \
long f = 1; \
int i; \
errno = 0; \
if (n_ < 0) \
printf("%d is negative, so it has no factorial\n", n_);\
else { \
for (i = 1; i <= n_; i++) { \
if (f > LONG_MAX / i) { \
printf("%d is too large for its factorial "\
"to be computed\n", n_);\
errno = ERANGE; \
break; \
} \
else \
f *= i; \
} \
if (errno != ERANGE) \
printf("Factorial of %d is %ld\n", n_, f);\
} \
} while (0) /*I'm not saying that it doesn't suck...*/

 

[Army1987]

Until you build it on a system whose int is 512 bit ;-)

#include <limits.h>
#include <errno.h>
long factorial(int n)
{
static long table[13] = { 1, 1, 2, 6, 24, 120, 720, 5040,
40320L, 362880L, 3628800L, 39916800L, 479001600L };
int i;
long f = table[12];
if (n < 0) {
errno = EDOM;
return n % 2 ? LONG_MIN : LONG_MAX;
}
if (n < 13) {
errno = 0;
return table[n];
}
for (i = 13; i <= n; i++) {
if (f > LONG_MAX / i) {
errno = ERANGE;
return LONG_MAX;
} else
f *= i;
}
errno = 0;
return f;
} /*rewrite this eliminating multiple returns if you feel like it*/

 

[Army1987]

WHICH COMPILER(S) DO YOU USE?

GCC and other C compilers now support many of the new features of C99.
However, there has been less support from vendors such as Microsoft
and Borland that have mainly focused on C++, since C++ provides
similar functionality improvement.

GCC, despite its extensive C99 support, is still not a completely
compliant implementation; several key features are missing or don't
work correctly

[...]

The above two paragraphs are an uncredited direct quote from a
Wikipedia article,
<http://en.wikipedia.org/wiki/C_(programming_language)>.

There's nothing wrong with quoting from outside sources, and the
quoted material happens to be correct,

and it happens to be relevant to the point, and the poster happens
to understand why it is and what it means...

 

[Keith Thompson]

If you really need to compute factorials, chances are you'll need them
for arguments that won't fit in any integer type, even if you have
512-bit integers.

Sorry, I meant that the result, not the argumement, won't necessarily
fit in any integer type.

 

[Net Nanny]

He also seems to have learnt the horrible habit of top-posting.

Please do not top-post. Your answer belongs after (or intermixed
with) the quoted material to which you reply, after snipping all
irrelevant material. See the following links:

--
<http://www.catb.org/~esr/faqs/smart-questions.html>
<http://www.caliburn.nl/topposting.html>
<http://www.netmeister.org/news/learn2quote.html>
<http://cfaj.freeshell.org/google/> (taming google)
<http://members.fortunecity.com/nnqweb/> (newusers)

You seem to have learnt the horrible habit of posting 9-line double
signatures.

Please do not post 9-line double signatures. Your signature should be at
most 4 lines long.

 

[Mark McIntyre]

#include <errno.h>
#define factorial(n) \

(snip macro that could suck bowling balls through a drinking straw)

} while (0) /*I'm not saying that it doesn't suck...*/

*phew*
--
Mark McIntyre

"Debugging is twice as hard as writing the code in the first place.
Therefore, if you write the code as cleverly as possible, you are,
by definition, not smart enough to debug it."
--Brian Kernighan

 

[Army1987]

(snip macro that could suck bowling balls through a drinking straw)


*phew*

Here is why I don't usually ever use the do { } while (0) trick.
If I cannot write a macro that expands to an expression, not even
abusing commas, &&s, ||s, ? :s and parentheses, then I write a
function. (And if I cannot write a macro that does not evalue each
argument exactly once, where each argument and the whole expression
is surrounded by as many parentheses as possibly ever needed, which
does not try to assign to or use the address of arguments etc.,
then I don't use lowercase in its name.)
Here I wanted to show that writing a macro that writes the
factorial of a number to stdout (other than
#define PRINT_FACT(n) (printf("Factorial of %d is %ld," (n),\
factorial(n)))
) albeit possible, isn't worth the trouble.

 

[osmium]

Which compiler do you use?
It's working fine in TC++ 3/4.5 & VC++ 6

Umesh, if you want to hold a conversation with someone via Usenet instead of
E-mail, you and your correspondent should both post to
alt.anonymous.messages, that's what the group is *for*. Doing so will avoid
the need for the rest of us to be subjected to the fragmentary, disorganized
thoughts you have from time to time.

Do you understand that "you" refers to one particular person, and not a
group of people collectively? Do you realize that you have not identified
that person?

 

[Richard Harter]

Incorrect. "You" may be a single person, or it may be a group of
people being addressed collectively, or it may be a generic "somebody"
(though I believe that "one" is the english-pedant-correct word to use
for that last one).

In formal usage you should use "one" but in informal usage one should use
"you".

 

[Dave Vandervies]

Do you understand that "you" refers to one particular person, and not a
group of people collectively?

Incorrect. "You" may be a single person, or it may be a group of
people being addressed collectively, or it may be a generic "somebody"
(though I believe that "one" is the english-pedant-correct word to use
for that last one).


dave