Determine if a character string is palindromic

[lovecreatesbeauty]

Hello experts,

I write a function named palindrome to determine if a character string
is palindromic, and test it with some example strings. Is it suitable
to add it to a company/project library as a small tool function
according to its quality? I will be very happy to get your suggestion
from every aspect on it: interface design, C language knowledge or
algorithm efficient.

Sincerely,

lovecreatesbeau ty
/* Filename : palindrome.c
* Function : bool palindrome(char *s);
* Description: to determine if a character string is palindromic
* Date : 8 May 2006
*/

#include <stdbool.h>
#include <stddef.h>
#include <string.h>

bool palindrome(char *s)
{
bool palindromic = true;
size_t len = strlen(s);

if (len > 1)
{
for (unsigned i = 0; i < len / 2; ++i)
{
if (s[i] != s[len - 1 - i])
{
palindromic = false;
break;
}
}
}

return palindromic;
}
/* test */
#include <stdio.h>

int main()
{
printf("%i\n", palindrome("dee d"));
printf("%i\n", palindrome("dee ds"));
}

/*
$ gcc -W -Wall -std=c99 -pedantic palindrome.c
$ ./a.out
1
0
$
*/

[Richard Tobin]

In article <44************ ***@yahoo.com>,
CBFalconer <cb********@mai neline.net> wrote:

/* null and empty strings are not palindromes */

Why on earth would you choose to not call the empty string a
palindrome? That would break such obvious invariants (indeed,
one might say definitions) as

palindrome(s) == (strcmp(s, reverse(s)) == 0)

-- Richard

[Chris F.A. Johnson]

On 2006-05-08, Keith Thompson wrote:

Finally, the only use I've ever seen for a function to determine
whether a string is a palindrome is as an exercise in a programming
class or other tutorial. I can't imagine including such a function,
however well implemented, in a library, or calling it other than in a
test of the function itself.

I use one in my work (composing cryptic crosswords).

--
Chris F.A. Johnson, author <http://cfaj.freeshell. org>
Shell Scripting Recipes: A Problem-Solution Approach (2005, Apress)
===== My code in this post, if any, assumes the POSIX locale
===== and is released under the GNU General Public Licence

[Keith Thompson]

"Chris F.A. Johnson" <cf********@gma il.com> writes:

On 2006-05-08, Keith Thompson wrote:

Finally, the only use I've ever seen for a function to determine
whether a string is a palindrome is as an exercise in a programming
class or other tutorial. I can't imagine including such a function,
however well implemented, in a library, or calling it other than in a
test of the function itself.

I use one in my work (composing cryptic crosswords).

Ok, sometimes my imagination fails me.

(Chris, just out of curiosity, why do you always indent everything you
write? Indentation like that is sometimes used to denote blocks of
quoted text. IMHO it would be clearer if your text were
left-justified like everyone else's.)

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

[Chris F.A. Johnson]

On 2006-05-08, Keith Thompson wrote:

"Chris F.A. Johnson" <cf********@gma il.com> writes:

On 2006-05-08, Keith Thompson wrote:

Finally, the only use I've ever seen for a function to determine
whether a string is a palindrome is as an exercise in a programming
class or other tutorial. I can't imagine including such a function,
however well implemented, in a library, or calling it other than in a
test of the function itself.
I use one in my work (composing cryptic crosswords).

Ok, sometimes my imagination fails me.

(Chris, just out of curiosity, why do you always indent everything you
write?

For the same reason that books have margins, and better books wider
margins.

Actaully, I started doing it in order to distinguish between my
text and (shell) code. I like code set flush left so that no
fiddling is necessary when cutting and pasting it.
Indentation like that is sometimes used to denote blocks of
quoted text.
Newsreaders, IME, generally do not recognize indentation as
quoting.
IMHO it would be clearer if your text were left-justified like
everyone else's.)

Left-justified? You mean flush-left and/or ragged right.

--
Chris F.A. Johnson, author <http://cfaj.freeshell. org>
Shell Scripting Recipes: A Problem-Solution Approach (2005, Apress)
===== My code in this post, if any, assumes the POSIX locale
===== and is released under the GNU General Public Licence

[CBFalconer]

Richard Tobin wrote:

CBFalconer <cb********@mai neline.net> wrote:

/* null and empty strings are not palindromes */

Why on earth would you choose to not call the empty string a
palindrome? That would break such obvious invariants (indeed,
one might say definitions) as

palindrome(s) == (strcmp(s, reverse(s)) == 0)

All I can say is I documented it. That has been lying about in my
junk directory for four years. To alter that, simply change 0 to 1
in one location.

--
"If you want to post a followup via groups.google.c om, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson
More details at: <http://cfaj.freeshell. org/google/>
Also see <http://www.safalra.com/special/googlegroupsrep ly/>

[Flash Gordon]

Chris F.A. Johnson wrote:

On 2006-05-08, Keith Thompson wrote:

"Chris F.A. Johnson" <cf********@gma il.com> writes:

On 2006-05-08, Keith Thompson wrote:
Finally, the only use I've ever seen for a function to determine
whether a string is a palindrome is as an exercise in a programming
class or other tutorial. I can't imagine including such a function,
however well implemented, in a library, or calling it other than in a
test of the function itself.
I use one in my work (composing cryptic crosswords). Ok, sometimes my imagination fails me.

(Chris, just out of curiosity, why do you always indent everything you
write?

For the same reason that books have margins, and better books wider
margins.

My news reader provides such indentation sufficient unto my needs. I
could probably configure it to provide more if I so desired. This does
not require that you indent your text.
Actaully, I started doing it in order to distinguish between my
text and (shell) code. I like code set flush left so that no
fiddling is necessary when cutting and pasting it.

Personally I find shells don't have a problem with white space before
the commands.

Indentation like that is sometimes used to denote blocks of
quoted text.

Newsreaders, IME, generally do not recognize indentation as
quoting.

Agreed.

IMHO it would be clearer if your text were left-justified like
everyone else's.)

Left-justified? You mean flush-left and/or ragged right.

Yes, the normal is flush-left and ragged right. Since it is the norm
news readers can reformat it as well.
--
Flash Gordon, living in interesting times.
Web site - http://home.flash-gordon.me.uk/
comp.lang.c posting guidelines and intro:
http://clc-wiki.net/wiki/Intro_to_clc

Inviato da X-Privat.Org - Registrazione gratuita http://www.x-privat.org/join.php

[CBFalconer]

"Chris F.A. Johnson" wrote:

On 2006-05-08, Keith Thompson wrote:

.... snip ...
(Chris, just out of curiosity, why do you always indent everything
you write?

For the same reason that books have margins, and better books wider
margins.

Actaully, I started doing it in order to distinguish between my
text and (shell) code. I like code set flush left so that no
fiddling is necessary when cutting and pasting it.

Indentation like that is sometimes used to denote blocks of
quoted text.

Newsreaders, IME, generally do not recognize indentation as
quoting.

IMHO it would be clearer if your text were left-justified like
everyone else's.)

Left-justified? You mean flush-left and/or ragged right.

Flush left. Your technique is fine until it gets requoted, when it
tends to spread out to the right, and be resistant to reformatting.

--
"If you want to post a followup via groups.google.c om, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson
More details at: <http://cfaj.freeshell. org/google/>
Also see <http://www.safalra.com/special/googlegroupsrep ly/>

[qed]

john wrote:

Robert Gamble wrote:

Robert Gamble wrote:

return 1;

That should be return 0;

}
}
}
return 0;

And that should be return 1;

Is there any particular reason that functions often behave this way?
If they succeed, they return 0, which in C is false, and vice versa.

Hmm, while I was writing this it occurred to me that it can have
something to do with error reporting. Different return values can
indicate different errors. Is that the reason?

It follows from a tradition in UNIX, however there is also a sound
reason for it. Very often a function returns with the *quantity* of
something it is trying to count from a complex data structure. However,
the data structure may be detectably corrupted or in an ill-defined
state. So using one int return value you can follow the convention that
all negative values indicate errors, and all positive values means
success -- further that all the positive values indicate each possible
count, while different negative values can correspond to different kinds
of errors.

So for example, how many elements are in a vector? Normally, you would
just want to know the quantity of elements that that vector has -- every
possibility from 0 to INT_MAX (say) makes sense, has meaning and easily
corresponds to a successful return. But if the vector is corrupted
because it has been ininitialized, or if an entry has some bad contents
or something like that you probably want some detail to help you track
down what kind of error you have, so that you can debug it, or avoid
that kind of vector contents. If you are just debugging, its usually
convenient to return -__LINE__. You can still reserve the value -1 for
other kinds of deterministic errors (like out of memory), since its
generally not possible to have source code which can expand the macro
__LINE__ on the first line of your source.

--
Paul Hsieh
http://www.pobox.com/~qed/
http://bstring.sf.net/

[Simon Biber]

Richard Heathfield wrote:

lovecreatesbeau ty said:

Hello experts,

I write a function named palindrome to determine if a character string
is palindromic, and test it with some example strings. Is it suitable
to add it to a company/project library as a small tool function
according to its quality? I will be very happy to get your suggestion
from every aspect on it: interface design, C language knowledge or
algorithm efficient.

You might want to test it with these well-known palindromes:

"Madam, I'm Adam!"
"Able was I, ere I saw Elba."
"A man, a plan, a canal - Panama!"

They are palindromic sentences, not palindromic strings.

void convert_sentenc e_to_string(cha r *destination, const char *source)
{
for(; *source; source++)
{
if(isalpha((uns igned char) *source))
*destination++ = toupper((unsign ed char) *source);
}
}

--
Simon.

[Richard Heathfield]

Simon Biber said:

Richard Heathfield wrote:

You might want to test it with these well-known palindromes:

"Madam, I'm Adam!"
"Able was I, ere I saw Elba."
"A man, a plan, a canal - Panama!"
They are palindromic sentences, not palindromic strings.

They are palindromes.
void convert_sentenc e_to_string(cha r *destination, const char *source)
{
for(; *source; source++)
{
if(isalpha((uns igned char) *source))
*destination++ = toupper((unsign ed char) *source);
}
}

And when were you planning on fixing the bug? :-)

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)