Re: Issues with setting variables to true or false: how does the compiler understands it

From	Bartc <bc@freeuk.com>
Newsgroups	comp.lang.c
Subject	Re: Issues with setting variables to true or false: how does the compiler understands it
Date	2015-10-26 23:39 +0000
Organization	A noiseless patient Spider
Message-ID	<n0mdfd$bbe$1@dont-email.me> (permalink)
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On 25/10/2015 18:56, Richard Heathfield wrote:

> Write a program that displays only the first n lines of its input.
>
> Write a program that displays only the /last/ n lines of its input.
> (Harder.)

Very hard I would have thought. What do you mean by 'its input'?

If that's interactive input, then it can go on for ever.

Also, clearly your exercises only make sense where the 'input' is 
actually a true line-oriented file where all lines are of 'reasonable' 
length, and where 'n' is also a 'reasonable' value. But I suspect too 
much of the code would be preoccupied with dealing with unreasonable input.

Actually, I think too much would still be tied up with low-level details 
as doing input in C is fiddly. Perhaps a more useful set of exercises 
(but more advanced) is creating a mini library that would then render 
the rest of the input exercises child's play in comparison.

(So the next 3 are just variations on string slicing, provided each line 
is allowed to reside in memory, and given some line-reading routine.)

> Write a program that displays only the leftmost n characters of each
> input line.
>
> Write a program that displays only the rightmost n characters of each
> input line. (Harder!)
>
> Write a program that displays only characters in columns x to y of each
> input line.

> Write a program that displays every other character of its input (either
> the 1st, 3rd, 5th, 7th etc or the 2nd, 4th, 6th, 8th etc at the user's
> discretion).

This suggests there is some actual interactive input, something else 
that can be tricky. Typical code I've seen in C is not line oriented: if 
three numbers are asked for, and only two are on this line, then it will 
wait for a subsequent line until all the inputs are satisfied. This is 
not very user friendly.

Line oriented user input will just return 0 or "" when it hits end-of-line.

-- 
Bartc

Thread

Issues with setting variables to true or false: how does the compiler understands it Alla _ <modelling.data@gmail.com> - 2015-10-24 02:17 -0700
  Issues with setting variables to true or false: how does the compiler understands it asetofsymbols@gmail.com - 2015-10-24 03:29 -0700
    Re: Issues with setting variables to true or false: how does the compiler understands it Alla _ <modelling.data@gmail.com> - 2015-10-24 03:38 -0700
  Re: Issues with setting variables to true or false: how does the compiler understands it Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-24 04:30 -0700
    Re: Issues with setting variables to true or false: how does the compiler understands it gazelle@shell.xmission.com (Kenny McCormack) - 2015-10-24 12:04 +0000
  Issues with setting variables to true or false: how does the compiler understands it asetofsymbols@gmail.com - 2015-10-24 04:59 -0700
    Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-24 14:28 +0100
      Re: Issues with setting variables to true or false: how does the compiler understands it asetofsymbols@gmail.com - 2015-10-24 07:26 -0700
        Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-24 17:06 +0100
  Re: Issues with setting variables to true or false: how does the compiler understands it James Kuyper <jameskuyper@verizon.net> - 2015-10-24 11:56 -0400
    Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-24 12:02 -0700
      Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-24 15:45 -0700
        Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-24 16:28 -0700
          Re: Issues with setting variables to true or false: how does the compiler understands it Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-24 16:44 -0700
            Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-24 19:34 -0700
          Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-24 19:30 -0700
            Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-24 20:33 -0700
          Re: Issues with setting variables to true or false: how does the compiler understands it Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-28 11:16 -0700
            Re: Issues with setting variables to true or false: how does the compiler understands it Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-10-28 15:12 -0400
              Re: Issues with setting variables to true or false: how does the compiler understands it Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-29 12:18 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it raltbos@xs4all.nl (Richard Bos) - 2015-10-29 21:51 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-30 08:38 -0700
              Re: Issues with setting variables to true or false: how does the compiler understands it Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-30 05:34 -0700
            Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-28 14:08 -0700
              Re: Issues with setting variables to true or false: how does the compiler understands it Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-30 06:14 -0700
            Re: Issues with setting variables to true or false: how does the compiler understands it glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-28 21:50 +0000
              Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-28 15:08 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-28 22:47 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Robert Wessel <robertwessel2@yahoo.com> - 2015-10-28 18:35 -0500
                Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-28 18:12 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-29 01:35 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Robert Wessel <robertwessel2@yahoo.com> - 2015-10-28 21:12 -0500
                Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-28 19:52 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-28 18:01 -0700
              Re: Issues with setting variables to true or false: how does the compiler understands it Tim Rentsch <txr@alumni.caltech.edu> - 2015-10-30 03:47 -0700
  Re: Issues with setting variables to true or false: how does the compiler understands it Barry Schwarz <schwarzb@dqel.com> - 2015-10-24 09:54 -0700
  Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-24 12:13 -0700
  Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-24 21:50 +0100
  Re: Issues with setting variables to true or false: how does the compiler understands it Alla _ <modelling.data@gmail.com> - 2015-10-25 04:04 -0700
    Re: Issues with setting variables to true or false: how does the compiler understands it Barry Schwarz <schwarzb@dqel.com> - 2015-10-25 08:32 -0700
      Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-25 18:19 +0000
      Re: Issues with setting variables to true or false: how does the compiler understands it Alla _ <modelling.data@gmail.com> - 2015-10-25 11:30 -0700
        Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-25 18:56 +0000
          Re: Issues with setting variables to true or false: how does the compiler understands it Alla _ <modelling.data@gmail.com> - 2015-10-25 20:59 -0700
            Re: Issues with setting variables to true or false: how does the compiler understands it Anand Hariharan <mailto.anand.hariharan@gmail.com> - 2015-10-25 21:49 -0700
              Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-26 08:10 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Anand Hariharan <mailto.anand.hariharan@gmail.com> - 2015-10-26 16:05 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-27 00:34 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-27 09:04 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-27 21:24 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-10-26 18:16 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-27 02:33 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-27 09:08 -0700
          Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-26 11:22 +0000
            Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-26 11:35 +0000
              Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-26 17:00 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-26 17:59 +0000
          Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-26 07:55 -0700
            Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-26 17:06 +0000
            Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-26 10:56 -0700
            Re: Issues with setting variables to true or false: how does the compiler understands it glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-10-26 20:14 +0000
              Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-26 17:09 -0700
          Re: Issues with setting variables to true or false: how does the compiler understands it Bartc <bc@freeuk.com> - 2015-10-26 23:39 +0000
            Re: Issues with setting variables to true or false: how does the compiler understands it Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-27 12:31 +0000
              Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-27 12:45 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-27 13:24 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-27 13:41 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-27 19:43 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-27 19:47 +0000
              Re: Issues with setting variables to true or false: how does the compiler understands it Bartc <bc@freeuk.com> - 2015-10-27 13:20 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Richard Heathfield <rjh@cpax.org.uk> - 2015-10-27 13:28 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-10-27 13:54 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-27 07:51 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it Bartc <bc@freeuk.com> - 2015-10-27 16:46 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-27 10:52 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it Bartc <bc@freeuk.com> - 2015-10-27 18:51 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-27 12:17 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it Bartc <bc@freeuk.com> - 2015-10-27 19:34 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-27 13:10 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-27 13:41 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it Bartc <bc@freeuk.com> - 2015-10-27 23:11 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-27 19:02 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it gazelle@shell.xmission.com (Kenny McCormack) - 2015-10-28 07:09 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-10-28 11:27 +0000
                Re: Issues with setting variables to true or false: how does the compiler understands it Keith Thompson <kst-u@mib.org> - 2015-10-27 12:27 -0700
                Re: Issues with setting variables to true or false: how does the compiler understands it supercat@casperkitty.com - 2015-10-27 13:18 -0700

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