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

Groups > comp.lang.c > #9168

Re: Is there a shorter solution ?

Show all headers | View raw

James Kuyper <jameskuyper@verizon.net> writes:
> On 08/10/2011 12:51 PM, HumbleWorker wrote:
>> 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:
>>>
>>> int main()
>>> {
>>>    char *k = "abababababawhatever";
>>>    while(*k) numA += *k++ == 'a';
>>>    printf("Number of a's = %d\n", numA);
>>>    return 0;
>>>
>>> }
>>>
>>> :-)
>> 
>> Thanks ! Is it guaranteed that a logical true returns 1 ?
>
> 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.

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.

The is*() functions declared in <ctype.h> are only defined to return 0
for false, and some unspecified non-zero value for true.  The same can
potentially apply to any expression used as a condition, unless its
top-level operator is one of the 9 listed above *or* it's specifically
written to yield only 0 or 1.

So:

if (x < y) count ++; // ok
count += (x < y);    // ok and equivalent to the above

if (isdigit(c)) count ++; // ok
count += !!isdigit(c);    // ok and equivalent to the above
count += isdigit(c);      // legal but *not* equivalent to the above

#define FALSE 0
#define TRUE 1             // useful if you don't have <stdbool.h>
int cond = isdigit(c);
if (cond == FALSE) ...;    // works, but unnecessarily verbose
if (cond == TRUE) ...;     // dangerous, fails if cond < 0 or cond > 1
if (cond) ...;             // the best way 

See also section section 9 of the comp.lang.c FAQ, <http://www.c-faq.com/>.

-- 
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"

Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

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

csiph-web