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From: Jay Martin <jaymmartin@earthlink.net>
Subject: Re: Software landmines (was: Why C++ is successful)
Date: 1998/08/16
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Date: 1998-08-16T00:00:00+00:00
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dennison@telepath.com wrote:
> 
> In article <dewar.903074236@merv>,
>   dewar@merv.cs.nyu.edu (Robert Dewar) wrote:
> > Andy said
> >
> > <<Ahh... but have you ever found a "good" reason for using it? I have used
> > goto in C and Pascal in certain rare cases, but I have always found clearer
> > ways to code these cases in Ada.
> > >>
> >
> > The two obvious uses vfor gotos in Ada are
> >
> > 1) to get a loop "continue" mechanism
> 
> for a simple loop, embedding the rest of the loop code in the body of the if
> statement is clearer. For nested loops where you want to "continue" an outer
> loop, I can see it. Not that I'd do such a thing. As a "goto-holic" who has
> been straight for 10 years, the best bet is abstinence. One day at a time. :-)
> 
> > For example, I find the following perfectly clear:
> >
> >    <<sort>> for J in 1 .. N - 1 loop
> >        if D (J) > D (J + 1) then
> >         Swap (D(J), D(J + 1));
> >           goto Sort;
> >        end if;
> >
> > It is a little tricky to program this without the goto and not make it
> > less clear. Actuallky many people who try this end up with a different
> > algorithm (hint: the above sort is cubic, it is NOT a quadratic bubble sort
> :-)
> 
> So the "average" poor maintainer schlep looks at this and thinks "is this
> just a continue, or a complete restarting of the loop?" Oh yeah, that's
> clear. %-(
> 
> If anyone does something this bizzare, they'd better put copious comments
> around it explaining its semantics. Otherwise, its the software equivalent of
> a land mine. Its just sitting there waiting for someone to touch it, then
> ...BOOM!
> 
> Very good counterexample to your own point.

Yup.

I'll take my stab at what I think the algorithm is doing.
I prefer flags and subroutines to gotos.

inline
void SwapFirstOutOfOrderElements(T D[], int N, bool& NoOutOfOrderElements) 
{
   NoOutOfOrderElements = true;
   for(int J = 0; J < (N-1); J++) {
      if (D[J] > D[J+1]) {
         Swap(D[J], D[J+1]);
         NoOutOfOrderElements = false;
         break;
      }//if//
   }//for//
}//SwapFirstOutOfOrderElements//

      
inline 
void SomeoneShootMeSort(T D[], int N) {    
   bool NoOutOfOrderElements;
   do {
      SwapFirstOutOfOrderElements(D, N, NoOutOfOrderElements);
   } while (!NoOutOfOrderElements);
}


Heh, its probably got a bug some where in there and
heh, do-while syntax sure sucks.  The subroutine name
is probably too short, maybe it should be
"ScanFromTheFrontOfTheArrayAndSwapTheFirstTwoAdjacentOutOfOrderElements".
No wait thats too short....


Maybe we should now go onto exponential time and random "highly
probable to be sorted" sorts.

Jay