Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.c > #9045 > unrolled thread

Is there a shorter solution ?

Back to article view | Back to comp.lang.c

Contents

  Is there a shorter solution ? HumbleWorker <amardeep.developer@gmail.com> - 2011-08-06 10:25 -0700
    Re: Is there a shorter solution ? Ike Naar <ike@sdf.lonestar.org> - 2011-08-06 17:42 +0000
    Re: Is there a shorter solution ? John Gordon <gordon@panix.com> - 2011-08-06 17:44 +0000
      Re: Is there a shorter solution ? Kenneth Brody <kenbrody@spamcop.net> - 2011-08-08 09:47 -0400
        Re: Is there a shorter solution ? Keith Thompson <kst-u@mib.org> - 2011-08-08 08:09 -0700
          Re: Is there a shorter solution ? HumbleWorker <amardeep.developer@gmail.com> - 2011-08-10 07:20 -0700
    Re: Is there a shorter solution ? tom st denis <tom@iahu.ca> - 2011-08-10 09:43 -0700
      Re: Is there a shorter solution ? HumbleWorker <amardeep.developer@gmail.com> - 2011-08-10 09:51 -0700
        Re: Is there a shorter solution ? James Kuyper <jameskuyper@verizon.net> - 2011-08-10 12:57 -0400
          Re: Is there a shorter solution ? HumbleWorker <amardeep.developer@gmail.com> - 2011-08-10 10:13 -0700
            Re: Is there a shorter solution ? blp@cs.stanford.edu (Ben Pfaff) - 2011-08-10 10:17 -0700
              Re: Is there a shorter solution ? HumbleWorker <amardeep.developer@gmail.com> - 2011-08-10 10:29 -0700
                Re: Is there a shorter solution ? tom st denis <tom@iahu.ca> - 2011-08-10 11:29 -0700
                  Re: Is there a shorter solution ? "J. J. Farrell" <jjf@bcs.org.uk> - 2011-08-11 03:02 +0100
              Re: Is there a shorter solution ? Kenneth Brody <kenbrody@spamcop.net> - 2011-08-12 11:39 -0400
                Re: Is there a shorter solution ? Keith Thompson <kst-u@mib.org> - 2011-08-12 09:06 -0700
            Re: Is there a shorter solution ? James Kuyper <jameskuyper@verizon.net> - 2011-08-10 14:00 -0400
            Re: Is there a shorter solution ? Seebs <usenet-nospam@seebs.net> - 2011-08-11 01:46 +0000
          Re: Is there a shorter solution ? Keith Thompson <kst-u@mib.org> - 2011-08-10 11:49 -0700
            Re: Is there a shorter solution ? James Kuyper <jameskuyper@verizon.net> - 2011-08-10 15:03 -0400
              Re: Is there a shorter solution ? Keith Thompson <kst-u@mib.org> - 2011-08-10 13:23 -0700
        Re: Is there a shorter solution ? gordonb.d3r7p@burditt.org (Gordon Burditt) - 2011-08-10 18:15 -0500
      Re: Is there a shorter solution ? HumbleWorker <amardeep.developer@gmail.com> - 2011-08-10 11:26 -0700
        Re: Is there a shorter solution ? James Kuyper <jameskuyper@verizon.net> - 2011-08-10 15:14 -0400

Page 2 of 2 — ← Prev page 1 [2]

#9171

James Kuyper <jameskuyper@verizon.net> writes:
> On 08/10/2011 02:49 PM, Keith Thompson wrote:
>> James Kuyper <jameskuyper@verizon.net> writes:
> ...
>>> All logical expressions in C indicate truth by having a result of 1.
>> 
>> For certain meanings of the phrase "logical expressions".
>> 
>> The <, <=, >, >=, ==, !=, !, &&, and || operators are all defined to
>> yield either 0 or 1.  I believe that's an exhaustive list.
>
> That's the meaning that I intended for "logical expressions".

I assumed so, but it's not clear from the phrase itself just what it
means; someone else might easily think of ``isdigit(c)'' as a logical
expression.  (The standard doesn't define the term.)

>> On the other hand, of course, a scalar expression used as a condition is
>> treated as false if it compares equal to 0, true otherwise.
>
> And that is not. I'd refer to those as conditions, not logical
> expressions. It's a distinction between what the value of an expression
> means (0: false, 1: true) and how the value of the expression is used
> (0: false, non-0: true).

That's a useful distinction, and it would be nice to have universally
agreed terms make that distinction.

> In a very different but somewhat C-like language, it would be
> philosophically cleaner to have logical expressions give results of
> boolean type; conditions constrained to take values of boolean type; and
> no conversions (neither implicit nor explicit) to or from the boolean
> type. The equivalent of C's implicit conversions could be done by
> 	non-boolean_value != 0
> 	boolean_value ? 1 : 0
> It would break way too much existing code to make any such change to C
> itself, of course.

Yes, and there are plenty of languages like that, though most of them
aren't particularly C-like (Pascal, Ada).  To avoid triggering a
language war, I'll just mention that I do personally prefer one approach
over the other without saying which.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Nokia
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

[toc] | [prev] | [next] | [standalone]

#9179

> Thanks ! Is it guaranteed that a logical true returns 1 ?

Yes, for only some things that return "logical true".

Operators such as &&, ||, <, >, ==, !=, <=, >=, and ! are guaranteed
to return 0 or 1.  (The comma operator is not included, although I
use commas to separate operators.) I do not guarantee that this is
a complete list.  Bitwise operators such as &, |, ^, and ~ do not
return "logical true", they return a number often viewed as a bit
pattern, although an expression like (flags & 0x0020) is sometimes
used as a "boolean".

The standard functions of the form is*() declared in <ctype.h> or
<wctype.h>, which you'd think return a "boolean" value, such as
isalpha() and isdigit(), return 0 or non-zero, *NOT* 0 or 1.  (C
doesn't really have a "boolean" type.  C99 "bool" is really a thinly
disguised integer.)  The same (0 or non-zero) applies to feof(),
ferror(), isfinite(), isinf(), isnan(), isnormal(), isgreater(),
isgreaterequal(), isless(), islessequal(), islessgreater(), and
isunordered().  I have probably left out some.

[toc] | [prev] | [next] | [standalone]

#9165

On Aug 10, 9:43 pm, tom st denis <t...@iahu.ca> wrote:
> On Aug 6, 1:25 pm, HumbleWorker <amardeep.develo...@gmail.com> wrote:
>
> > Count the number of a in cX below
>
> > #include <stdio.h>
>
> > int main()
> > {
> >         char cX[] = "ababcabcdabcaba", * k = cX;
> >         int numA = 0;
> >         while (*k && ('a' == *k++ ? ++numA : 1));
> >         printf ("Number of a's = %u\n", numA);
> >         return 0;
> > }
>
> Um shorter eh ...
>
> int numA;
> int main()
> {
>    char *k = "abababababawhatever";
>    while(*k) numA += *k++ == 'a';
>    printf("Number of a's = %d\n", numA);
>    return 0;
>
> }
>
> :-)

I am curious about one more thing. What would be the considerations of
efficiency when we use a for loop like this instead of the while loop
above ?

int main()
{
	int numA = 0;
	char* k = "abababababawhatever";
	for (; *k; numA += *k++ == 'a');
	printf("Number of a's = %d\n", numA);
	return 0;
}

[toc] | [prev] | [next] | [standalone]

#9170

On 08/10/2011 02:26 PM, HumbleWorker wrote:
> On Aug 10, 9:43 pm, tom st denis <t...@iahu.ca> wrote:
...
>> int numA;
>> int main()
>> {
>>    char *k = "abababababawhatever";
>>    while(*k) numA += *k++ == 'a';
>>    printf("Number of a's = %d\n", numA);
>>    return 0;
>>
>> }
>>
>> :-)
> 
> I am curious about one more thing. What would be the considerations of
> efficiency when we use a for loop like this instead of the while loop
> above ?
> 
> int main()
> {
> 	int numA = 0;
> 	char* k = "abababababawhatever";
> 	for (; *k; numA += *k++ == 'a');
> 	printf("Number of a's = %d\n", numA);
> 	return 0;
> }

The while-for conversion has no efficiency implications. Those parts of
the two programs are precisely equivalent, and if you're using a
compiler that isn't smart enough to recognize that fact and optimize
them the same way, you've got much bigger problems than simple
optimization to worry about.

[toc] | [prev] | [standalone]

Page 2 of 2 — ← Prev page 1 [2]

Back to top | Article view | comp.lang.c

csiph-web