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Re: OT: improve this simple algorithm?

From David Brown <david.brown@hesbynett.no>
Newsgroups comp.lang.c
Subject Re: OT: improve this simple algorithm?
Date 2019-11-13 10:52 +0100
Organization A noiseless patient Spider
Message-ID <qqgjo2$od6$1@dont-email.me> (permalink)
References <C_EyF.8877$yS5.1510@fx22.iad> <AmFyF.247755$GwW.209873@fx08.am4> <CDLyF.5898$ej.367@fx18.iad>

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On 13/11/2019 05:28, DFS wrote:

> 
> I understand there "is no string type in C", but all that work to assign
> an array of chars to an array position?
> 

The main point to understand is that there is no automatic memory
management in C.  If you need to store things with different sizes, you
have to allocate memory for them along the way - using malloc or related
functions.  And you have to free the memory after use.  (In most
systems, once the program stops all allocated memory will be freed by
the OS - but you should get in the habit of doing it correctly in the
program.)

You are learning C.  That means you need to understand these things, and
practice them.  You need to get the hang of when you need to allocate
memory and when to free it, and when you can pretend that a "char *" is
a bit like a string in the sense used by other languages, and when it is
not.

You need to build up a collection of functions that you have made (or
acquired) and understand, and can re-use.  So take Bart's "allocstring"
function and keep it (though I recommend being more generous with spaces
than Bart is - make your code as readable as possible).  Don't inline it
into the rest of your code.  That is the compiler's job.

And throw out your toy compilers.  Use a /good/ compiler - clang or gcc.
 Use its features well.  Use its warnings, and its optimisations (which
enable better warnings).  Use the sanitizers - look these up in the
reference manual for the compiler.  These will often tell you when you
are doing something bad, such as memory leaks, overflows, bad
conversions, etc.  They can be a big help in learning the language and
good programming habits.


If you are not trying to learn C specifically, and just want to learn
some programming to solve these kinds of programs, then C is definitely
the wrong choice of language.  You then want a language that handles
strings, memory allocation, sorting, lists, etc., at a higher level.
For example, a Python solution for your program here can be written in a
single line function :

def gaps(ns) :
    [(s + 1, t - 1) for (s, t) in zip(ns[:-1], ns[1:]) if (t - s) > 1]

gaps([1, 2, 4, 5, 7, 12, 1300, 10000])

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OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-12 15:55 -0500
  Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-12 21:20 +0000
    Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-12 23:28 -0500
      Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-13 10:52 +0100
        Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-13 10:16 -0500
          Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-13 16:53 +0100
      Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-13 11:18 +0000
  Re: OT: improve this simple algorithm? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-12 23:30 +0000
    Re: OT: improve this simple algorithm? Ian Collins <ian-news@hotmail.com> - 2019-11-15 05:12 +1300
      Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 16:34 +0000
        Re: OT: improve this simple algorithm? Ian Collins <ian-news@hotmail.com> - 2019-11-15 10:07 +1300
          Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 22:25 +0000
            Re: OT: improve this simple algorithm? Ian Collins <ian-news@hotmail.com> - 2019-11-15 12:02 +1300
              Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 23:27 +0000
                Re: OT: improve this simple algorithm? Ian Collins <ian-news@hotmail.com> - 2019-11-15 19:06 +1300
                Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-15 10:45 +0000
                Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-15 13:28 +0100
                Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-15 12:58 +0000
                Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-15 15:39 +0100
                Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-15 15:04 +0000
                Re: OT: improve this simple algorithm? Richard Damon <Richard@Damon-Family.org> - 2019-11-15 12:19 -0500
                Re: OT: improve this simple algorithm? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-11-15 09:46 -0800
                Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-15 18:59 +0000
                Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-16 11:59 +0000
                Re: OT: improve this simple algorithm? Ian Collins <ian-news@hotmail.com> - 2019-11-16 09:02 +1300
              Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-15 11:17 +0100
                Re: OT: improve this simple algorithm? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-11-15 21:38 +0000
    Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-14 11:44 -0500
      Re: OT: improve this simple algorithm? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-14 18:11 +0000
        Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-14 13:33 -0500
          Re: OT: improve this simple algorithm? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-15 01:49 +0000
      Re: OT: improve this simple algorithm? Barry Schwarz <schwarzb@delq.com> - 2019-11-14 10:38 -0800
    Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-14 12:56 -0500
      Re: OT: improve this simple algorithm? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-14 13:50 -0500
        Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-14 14:42 -0500
          Re: OT: improve this simple algorithm? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-14 15:25 -0500
      Re: OT: improve this simple algorithm? Barry Schwarz <schwarzb@delq.com> - 2019-11-14 11:03 -0800
        Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-14 16:08 -0500
          Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-15 11:30 +0100
            Re: OT: improve this simple algorithm? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-15 11:17 +0000
              Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-15 17:35 -0500
                Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-15 17:39 -0500
                Re: OT: improve this simple algorithm? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-15 23:19 +0000
                Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-15 18:53 -0500
                Re: OT: improve this simple algorithm? Richard Damon <Richard@Damon-Family.org> - 2019-11-15 19:08 -0500
                Re: OT: improve this simple algorithm? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-16 01:30 +0000
                Re: OT: improve this simple algorithm? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-16 07:39 -0500
                Re: OT: improve this simple algorithm? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-16 07:37 -0500
          Re: OT: improve this simple algorithm? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-15 09:46 -0500
            Re: OT: improve this simple algorithm? Richard Damon <Richard@Damon-Family.org> - 2019-11-15 12:38 -0500
              Re: OT: improve this simple algorithm? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-15 23:07 +0000
              Re: OT: improve this simple algorithm? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-11-28 16:54 -0800
                Re: OT: improve this simple algorithm? Richard Damon <Richard@Damon-Family.org> - 2019-11-28 20:17 -0500
                Re: OT: improve this simple algorithm? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-11-29 06:08 -0800
      Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 20:45 +0100
    Re: OT: improve this simple algorithm? Keith Thompson <kst-u@mib.org> - 2019-11-14 10:10 -0800
      Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 20:19 +0100
    Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-12 23:57 -0500
      Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-13 10:34 +0100
    Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-13 23:57 -0500
      Re: OT: improve this simple algorithm? Barry Schwarz <schwarzb@delq.com> - 2019-11-13 23:00 -0800
      Re: OT: improve this simple algorithm? Ike Naar <ike@sdf.lonestar.org> - 2019-11-14 07:53 +0000
        Re: OT: improve this simple algorithm? guinness.tony@gmail.com - 2019-11-14 02:34 -0800
      Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 10:01 +0100
        Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 11:27 +0000
          Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 12:46 +0100
            Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 12:01 +0000
              Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 14:05 +0100
  Re: OT: improve this simple algorithm? Barry Schwarz <schwarzb@delq.com> - 2019-11-12 18:34 -0800
    Re: OT: improve this simple algorithm? Keith Thompson <kst-u@mib.org> - 2019-11-12 19:01 -0800
      Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 17:08 +0100
        Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 17:06 +0000
        Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 19:11 +0000
      Re: OT: improve this simple algorithm? Ian Collins <ian-news@hotmail.com> - 2019-11-15 05:15 +1300
      Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 18:13 +0000
        Re: OT: improve this simple algorithm? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-14 20:16 +0100
          Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 20:03 +0000
            Re: OT: improve this simple algorithm? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-15 04:51 +0100
      Re: OT: improve this simple algorithm? Keith Thompson <kst-u@mib.org> - 2019-11-14 10:15 -0800
        Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 20:52 +0100
      Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-13 10:57 +0100
        Re: OT: improve this simple algorithm? Ian Collins <ian-news@hotmail.com> - 2019-11-13 23:23 +1300
        Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-13 11:53 +0000
          Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-13 14:02 +0100
            Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-13 13:40 +0000
              Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-13 17:01 +0100
                Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-13 16:28 +0000
                Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-13 22:49 +0100
                Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-13 22:38 +0000
                Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-13 23:06 +0000
                Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 10:10 +0100
                Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 10:42 +0000
                Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 12:53 +0100
                Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 12:28 +0000
                Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 14:21 +0100
                Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 14:28 +0000
                Re: OT: improve this simple algorithm? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-14 15:38 +0100
                Re: OT: improve this simple algorithm? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-14 13:37 +0100
                Re: OT: improve this simple algorithm? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-14 13:38 +0100
          Re: OT: improve this simple algorithm? Thiago Adams <thiago.adams@gmail.com> - 2019-11-13 05:21 -0800

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