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Re: selection-sort in C

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arnuld <sunrise@invalid.address> writes:

> Just wrote selection-sort in C. Is it the right way to do this in C ?
> 
> (definition of selection-sort taken from exercise 2.2-2 of Introduction 
> to Algorithms, 2e)
> 
> 
> /* Exercise 2.2-2, page 29, Selection Sort */
> 
> #include <stdio.h>
> 
> enum { SIZE_ARR = 6 };
> 
> void selectionSort(char s[], int len);
> int findSmallest(char s[], const int idx_cur, const int len);

The consts on those parameters don't do much, but aren't actually
wrong.

> 
> 
> int main(void)
> {
>   char arr[SIZE_ARR+1] = {'a', 'r', 'n', 'u', 'l', 'd'};
>   
>   printf("%s\n", arr);
>   selectionSort(arr, SIZE_ARR); 
>   printf("%s\n", arr);
> 
>   return 0;
> }
> 
> 
> void selectionSort(char s[], int len)
> {
>   int i, idx;
>   char tmp;

Schools of thought vary, but some prefer variables that are only
going to be used in a small scope to be declared within that scope.

>   for(i = 0; i != len; ++i)
>     {
>       idx = findSmallest(s, i, len);

so that could be 
        int idx = findSmallest(s, i, len);

>       /*      printf("i = %d, Smallest Index = %d, s[%d] = %c\n", i, idx, 
> idx, s[idx]); */
>       tmp = s[i];

and that could be 
        char tmp = s[i];

>       s[i] = s[idx];
>       s[idx] = tmp;

Note that the swap is only necessary if(i != idx).

>     }
> }
> 
> 
> int findSmallest(char s[], const int idx_cur, const int len)
> {
>   int j, ret_index;
>   char smallest = s[idx_cur];
>   ret_index = idx_cur;
> 
>   for(j = idx_cur+1; j != len; ++j)
>     {
>       /*      printf("idx_cur = %d, j = %d\n", idx_cur, j); */
>       if(smallest > s[j])

Again, it's a matter of taste, but some prefer the object
you're testing to be first in the comparison. And here you're
testing s[j]. So:

        if(s[j] < smallest)

> 	{
> 	  smallest = s[j];
> 	  ret_index = j;
> 	}
>     }
> 
>   return ret_index;
> }

The sort looks fine. You might want to write a simple test 
harness to test arbitrary inputs.

Phil
-- 
Humans will have advanced a long, long, way when religious
belief has a cozy little classification in the DSM.
-- David Melville (on r.a.s.f1)

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selection-sort in C arnuld <sunrise@invalid.address> - 2011-08-16 11:08 +0000
  Re: selection-sort in C Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-08-16 14:24 +0300
    Re: selection-sort in C arnuld <sunrise@invalid.address> - 2011-08-16 11:36 +0000
      Re: selection-sort in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-08-16 13:22 +0100
        Re: selection-sort in C arnuld <sunrise@invalid.address> - 2011-08-16 13:44 +0000
          Re: selection-sort in C Anand Hariharan <mailto.anand.hariharan@gmail.com> - 2011-08-16 07:36 -0700
        Re: selection-sort in C Thomas Boell <tboell@domain.invalid> - 2011-08-16 18:03 +0200
          Re: selection-sort in C karnath <karnathtorjian@gmail.com> - 2011-08-16 16:25 +0000
            Re: selection-sort in C Willem <willem@toad.stack.nl> - 2011-08-16 16:33 +0000
          Re: selection-sort in C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2011-08-16 20:03 +0100
        Re: selection-sort in C Keith Thompson <kst-u@mib.org> - 2011-08-16 09:27 -0700
      Re: selection-sort in C Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-08-17 20:17 +0000
        Re: selection-sort in C pete <pfiland@mindspring.com> - 2011-08-18 00:41 -0400
          Re: selection-sort in C Ben Pfaff <blp@cs.stanford.edu> - 2011-08-17 21:52 -0700
            Re: selection-sort in C pete <pfiland@mindspring.com> - 2011-08-18 01:07 -0400
              Re: selection-sort in C blp@cs.stanford.edu (Ben Pfaff) - 2011-08-17 22:36 -0700
                Re: selection-sort in C pete <pfiland@mindspring.com> - 2011-08-18 07:00 -0400
    Re: selection-sort in C BGB <cr88192@hotmail.com> - 2011-08-16 14:41 -0700
      Re: selection-sort in C Ian Collins <ian-news@hotmail.com> - 2011-08-17 10:10 +1200
        Re: selection-sort in C BGB <cr88192@hotmail.com> - 2011-08-16 17:25 -0700
          Re: selection-sort in C pacman@kosh.dhis.org (Alan Curry) - 2011-08-17 01:53 +0000
  Re: selection-sort in C Gene <gene.ressler@gmail.com> - 2011-08-16 05:27 -0700
  Re: selection-sort in C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2011-08-16 07:24 -0700
  Re: selection-sort in C pete <pfiland@mindspring.com> - 2011-08-16 19:22 -0400
    Re: selection-sort in C arnuld <sunrise@invalid.address> - 2011-08-17 07:52 +0000
      Re: selection-sort in C Angel <angel+news@spamcop.net> - 2011-08-17 10:15 +0000
      Re: selection-sort in C Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-08-17 13:22 +0300
      Re: selection-sort in C pete <pfiland@mindspring.com> - 2011-08-18 00:33 -0400

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