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From: mouse@mcgill-vision.UUCP (der Mouse)
Newsgroups: net.lang.c
Subject: Re: goto jumps into loops
Message-ID: <412@mcgill-vision.UUCP>
Date: Mon, 21-Apr-86 00:20:26 EST
Article-I.D.: mcgill-v.412
Posted: Mon Apr 21 00:20:26 1986
Date-Received: Thu, 24-Apr-86 07:09:35 EST
References: <69@brl-smoke.ARPA>
Organization: McGill University, Montreal
Lines: 91
Summary: goto-less way which is *shorter* and *cleaner* as well

In article <69@brl-smoke.ARPA>, dmh@mit-borax.ARPA (David Harmon) writes:
> [...] I need to print out all the elements of a set capable of containing
> or not containing any value from 0..255.
> [...] but I also wanted to contract adjacent members of a set into a range
> syntax.
>
> /* Assume the existence of a type named "set", which is intended to simulate
>    the Pascal TYPE KeySet:SET OF 0..255;
>    Further assume the existence of a function
>  in(e,l);
>  set *l;
>  char e;
> which returns a boolean 1 iff _e_ is an element of _*l_.
> */
> [48-line example, using obscure goto, deleted]

     I  once wrote some code  which did something similar; adapting this
to your problem....  As far as I  can tell  from your code (it's not the
easiest  thing in the world to understand),  you want spaces  instead of
commas.  For example, you want
	1 3 5-10
not
	1,3,5-10
I am also taking the liberty of producing a leading space, that is, this
code produces
	" 1 3 5-10"
instead of
	"1 3 5-10"
This can be fixed with two more lines (a boolean variable and  some code
to use it).

     This is only 26 lines  (saving of 22), and it is understandable (by
comparison).   Five more lines can be trimmed out if you  are willing to
sacrifice a  smidgen of speed by calling  in() more often than is really
necessary:

	- delete the declarations of isin and oldin
	- delete the initialization of oldin
	- delete the oldin=isin assignment
	- change these three lines
		  { isin = (i==MAX) ? 0 : in(listp,i);
		    if (isin != oldin)
		     { if (isin)
	  to these two
		  { if (((i==MAX)?0:in(listp,i)) != ((i==0)?0:in(listp,i-1)))
		     { if ((i==MAX)?0:in(listp,i))

The messy `?:' operators in the last change  above  (and in the original
assignment to isin) can be eliminated  if in() is guaranteed to return 0
for out-of-bounds values  of e. Just replace  the entire `?:' expression
with the call to in() contained in the `else' part.

     Without further ado, here is the code:

#define MAX NUM_KEYWORDS   /*The highest element in use by the application*/
wrtlist(listp)
set *listp;
{
 int i;
 int j;
 int isin;
 int oldin;

 oldin = 0;
 for (i=0;i<=MAX;i++)
  { isin = (i==MAX) ? 0 : in(listp,i);
    if (isin != oldin)
     { if (isin)
	{ printf(" %d",i);
	  j = i;
	}
       else
	{ if (j < i-1)
	   { printf("-%d",i-1);
	   }
	}
     }
    oldin = isin;
  }
}
-- 
					der Mouse

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