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Re: Pointers: misunderstanding

From Keith Thompson <kst-u@mib.org>
Newsgroups comp.lang.c
Subject Re: Pointers: misunderstanding
Date 2015-11-07 12:24 -0800
Organization None to speak of
Message-ID <lnio5d1rsp.fsf@kst-u.example.com> (permalink)
References <982998f5-5ccc-4bbb-9c57-281252c80a8a@googlegroups.com> <38d3fcac-3453-4b66-a476-a5b7ed697ebd@googlegroups.com>

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Alla _ <modelling.data@gmail.com> writes:
> Here is the final version that has temp in it (I now have also the one
> without temp variable). I am sorry if I missed something, but I still don't 
> see why the program doesn't swap 6 and 0.
>
> The array before the sort:
> 34 -5 6 0 12 100 
> The array after the sort: 
> -5 6 0 12 34 100
>
> // Program to sort an array of integers into ascending order
>
> #include <stdio.h>
>
> void sort (int* array_int, int n)
> {
>     int temp;
>     int* pointer_1 = array_int;
>     int* array_end = &array_int[n - 1];
>     int* pointer_2 = pointer_1 + 1;
>     
>     while (pointer_1 < array_end - 1)
>     {
>         while(pointer_2 < array_end)
>         {
>             if (*pointer_1 > *pointer_2)
>             {
>                 temp = *pointer_1;
>                 *pointer_1 = *pointer_2;
>                 *pointer_2 = temp;
>             }
>             pointer_1++;
>             pointer_2++;
>         }
>     }
>         
> }
>
> int main (void)
[...]

Initialliy, pointer_1 points to the initial element of the array and
pointer_2 points to the element immediately following it.

The only time they're changed, they're both incremented together, which
means that pointer_1 and pointer_2 always point to adjacent elements,
and they only advance from the beginning of the array to its end.

The only changes you make to elements of the array is to swap the
elements pointed to by element_1 and element_2.

Suppose you start with the smallest value at the end of the array.
Given the above, it might be swapped into the second-to-last position,
but it can never be moved earlier than that.

-- 
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"

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Thread

Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-05 09:09 -0800
  Re: Pointers: misunderstanding Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-05 17:44 +0000
    Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 00:49 -0800
      Re: Pointers: misunderstanding Philip Lantz <prl@canterey.us> - 2015-11-06 03:01 -0800
        Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 03:09 -0800
  Re: Pointers: misunderstanding Barry Schwarz <schwarzb@dqel.com> - 2015-11-05 11:40 -0800
  Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 03:08 -0800
    Re: Pointers: misunderstanding Richard Heathfield <rjh@cpax.org.uk> - 2015-11-06 11:33 +0000
    Re: Pointers: misunderstanding Keith Thompson <kst-u@mib.org> - 2015-11-06 08:53 -0800
  Re: Pointers: misunderstanding Philip Lantz <prl@canterey.us> - 2015-11-06 03:16 -0800
    Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 03:30 -0800
      Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 03:32 -0800
        Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 04:58 -0800
          Re: Pointers: misunderstanding Keith Thompson <kst-u@mib.org> - 2015-11-06 09:00 -0800
            Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 09:25 -0800
            Re: Pointers: misunderstanding supercat@casperkitty.com - 2015-11-06 10:07 -0800
              Re: Pointers: misunderstanding Keith Thompson <kst-u@mib.org> - 2015-11-06 12:31 -0800
              Re: Pointers: misunderstanding Philip Lantz <prl@canterey.us> - 2015-11-06 20:08 -0800
        Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 04:59 -0800
      Re: Pointers: misunderstanding Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-06 13:06 +0000
        Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 08:50 -0800
          Re: Pointers: misunderstanding Richard Heathfield <rjh@cpax.org.uk> - 2015-11-06 17:00 +0000
            Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 09:17 -0800
              Re: Pointers: misunderstanding Richard Heathfield <rjh@cpax.org.uk> - 2015-11-06 17:22 +0000
                Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 09:29 -0800
              Re: Pointers: misunderstanding Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-06 17:53 +0000
            Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 09:22 -0800
              Re: Pointers: misunderstanding Richard Heathfield <rjh@cpax.org.uk> - 2015-11-06 17:24 +0000
                Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 09:33 -0800
                Re: Pointers: misunderstanding Richard Heathfield <rjh@cpax.org.uk> - 2015-11-06 18:29 +0000
                Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 23:42 -0800
            Re: Pointers: misunderstanding Philip Lantz <prl@canterey.us> - 2015-11-06 20:24 -0800
          Re: Pointers: misunderstanding Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-06 17:51 +0000
            Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 23:37 -0800
              Re: Pointers: misunderstanding Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-07 13:36 +0000
                Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-07 08:17 -0800
                Re: Pointers: misunderstanding Philip Lantz <prl@canterey.us> - 2015-11-07 12:04 -0800
    Re: Pointers: misunderstanding Keith Thompson <kst-u@mib.org> - 2015-11-06 08:55 -0800
      Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 09:23 -0800
  Re: Pointers: misunderstanding Philip Lantz <prl@canterey.us> - 2015-11-06 03:26 -0800
  Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 23:48 -0800
    Re: Pointers: misunderstanding Barry Schwarz <schwarzb@dqel.com> - 2015-11-07 00:35 -0800
  Re: Pointers: misunderstanding Alla _ <modelling.data@gmail.com> - 2015-11-06 23:48 -0800
    Re: Pointers: misunderstanding Keith Thompson <kst-u@mib.org> - 2015-11-07 12:24 -0800

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