Re: Printing like palindrome

From	Keith Thompson <kst-u@mib.org>
Newsgroups	comp.lang.c
Subject	Re: Printing like palindrome
Date	2017-05-09 12:33 -0700
Organization	None to speak of
Message-ID	<lntw4t965w.fsf@kst-u.example.com> (permalink)
References	<5911a0f4$0$294$14726298@news.sunsite.dk> <p093hc1ll75lunca1bsh8k9ahd7efpvduq@4ax.com> <tl44hchl4uroj983a5pbvd0sseovn611dg@4ax.com>

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Robert Wessel <robertwessel2@yahoo.com> writes:
[...]
> Is that sufficient?  I know C doesn't require A..Z to be contiguous,
> but does it require the alphabet to be in ascending order in the
> character set?  I'm not aware that it does (the requirements for the
> digits to be ascending and contiguous is quite explicit and specific).

It doesn't.  Both EBCDIC and the various ASCII-based character sets do
have the letters in order, but there's no such requirement.

> I know of character sets where the letters are not in the conventional
> order (that various Baudot codes, for example), but I don't know of
> any implementations of C that actually use such.

Nor do I.

But if you want to write code that doesn't make any such assumptions,
you can define an array:
    const char upper[26] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
and iterate over it.

Of course you *can* just assume that the letters are contiguous and
ordered, but if you do I suggest clearly documenting the assumption,
and perhaps even checking it ('Z' - 'A' == 25 isn't a perfect test,
but it's something).

You might also think about non-Latin letters.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

Thread

Printing like palindrome arnuld <sunrise@invalid.address> - 2017-05-09 10:59 +0000
  Re: Printing like palindrome Barry Schwarz <schwarzb@dqel.com> - 2017-05-09 04:26 -0700
    Re: Printing like palindrome Robert Wessel <robertwessel2@yahoo.com> - 2017-05-09 14:10 -0500
      Re: Printing like palindrome Keith Thompson <kst-u@mib.org> - 2017-05-09 12:33 -0700
        Re: Printing like palindrome Richard Heathfield <rjh@cpax.org.uk> - 2017-05-09 23:05 +0100
          Re: Printing like palindrome raltbos@xs4all.nl (Richard Bos) - 2017-05-10 10:25 +0000
            Re: Printing like palindrome Richard Heathfield <rjh@cpax.org.uk> - 2017-05-10 11:44 +0100
          Re: Printing like palindrome Keith Thompson <kst-u@mib.org> - 2017-05-10 09:48 -0700
            Re: Printing like palindrome Gareth Owen <gwowen@gmail.com> - 2017-05-10 18:59 +0100
        Re: Printing like palindrome arnuld <sunrise@invalid.address> - 2017-05-12 07:14 +0000
      Re: Printing like palindrome arnuld <sunrise@invalid.address> - 2017-05-12 07:44 +0000
    Re: Printing like palindrome arnuld <sunrise@invalid.address> - 2017-05-12 07:20 +0000
      Re: Printing like palindrome Keith Thompson <kst-u@mib.org> - 2017-05-12 08:49 -0700
        Re: Printing like palindrome arnuld <sunrise@invalid.address> - 2017-05-14 02:01 +0000
  Re: Printing like palindrome mark.bluemel@gmail.com - 2017-05-09 07:13 -0700
    Re: Printing like palindrome scott@slp53.sl.home (Scott Lurndal) - 2017-05-09 14:59 +0000
      Re: Printing like palindrome Keith Thompson <kst-u@mib.org> - 2017-05-09 08:27 -0700
      Re: Printing like palindrome Barry Schwarz <schwarzb@dqel.com> - 2017-05-09 10:40 -0700
  Re: Printing like palindrome scott@slp53.sl.home (Scott Lurndal) - 2017-05-09 14:38 +0000
    Re: Printing like palindrome Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-09 22:48 +0100
      Re: Printing like palindrome scott@slp53.sl.home (Scott Lurndal) - 2017-05-10 13:21 +0000
        Re: Printing like palindrome Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-05-10 15:45 +0100
        Re: Printing like palindrome Barry Schwarz <schwarzb@dqel.com> - 2017-05-10 10:26 -0700
  Re: Printing like palindrome bartc <bc@freeuk.com> - 2017-05-09 21:28 +0100
    Re: Printing like palindrome raltbos@xs4all.nl (Richard Bos) - 2017-05-10 10:27 +0000
    Re: Printing like palindrome Chad <cdalten@gmail.com> - 2017-05-10 10:39 -0700
  Re: Printing like palindrome bartc <bc@freeuk.com> - 2017-05-10 12:54 +0100
  Printing like palindrome asetofsymbols@gmail.com - 2017-05-12 02:32 -0700

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