Re: BBC and DEFINT etc [Was: Using GOTO]

<news@[EMAIL PROTECTED]
> wrote:
> "Judson McClendon" <ju...@[EMAIL PROTECTED]
> wrote:
>> One thing that surprised me is the behavior of FOR/NEXT, in always
making
>> one iteration, regardless of the initial loop variables. I don't recall
ever using
>> a BASIC, or any other language sup****ting FOR, with that behavior.
>
> On the contrary, my recollection is that it was the normal behaviour
> at the time BBC BASIC was specified.
>
>> It is very counter intuitive.
>
> I disagree.  I can see no reason to anticipate any particular
> behaviour when the initial conditions are meaningless.  A statement
> such as FOR i = 3 TO 2 doesn't imply that the loop should be skipped,
> it has no logical meaning at all.  'Intuitively' the situation should
> never be allowed to arise.

But the initial conditions aren't meangless, they're simply false. The
begin, end and step values can all be variables, determined at runtime.
They may very well be meangful and logically correct, based on the
particular process. Something similar to a Quicksort, perhaps.

> It is clear that a REPEAT..UNTIL (or DO..WHILE) loop performs the test
> at the end of the loop, and hence must execute the body of the loop at
> least once.  On the other hand a WHILE..ENDWHILE (WHILE..WEND) loop
> performs the test at the beginning, and may not execute the body of
> the loop at all.  FOR..NEXT is neither one nor the other, and I can't
> see why it should preferentially be placed in either category.

In "DO ... WHILE (condition)" the termination condition is located at the
bottom of the loop, and is tested at the bottom of the loop.

IN "WHILE (condition) ... ENDWHILE" the termination condition is
located at the top of the loop, and is tested at the top of the loop.

In "FOR n  = begin TO end (condition) [STEP step] ... NEXT n" the
termination condition is located at the top of the loop, and should be
tested at the top of the loop. I believe doing otherwise violates the
Rule (or Law or Principle) of Least Astonishment. :-)
-- 
Judson McClendon      judmc@[EMAIL PROTECTED]
 (remove zero)
Sun Valley Systems     http://sunvaley.com
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