Re: basic BASIC question

In article <679d26bd$0$713$14726298@news.sunsite.dk>,
Arne Vajhøj  <arne@vajhoej.dk> wrote:

On 1/31/2025 2:24 PM, Dan Cross wrote:

In article <679d001e$0$713$14726298@news.sunsite.dk>,
Arne Vajhøj  <arne@vajhoej.dk> wrote:

On 1/31/2025 11:39 AM, Dave Froble wrote:

On 1/31/2025 10:18 AM, Arne Vajhøj wrote:

Is it common to use:
>
declare integer constant TRUE = -1
declare integer constant FALSE = 0
>
>
?

>
It works.  Doesn't really matter if declared a constant.  Zero is false,
anything else is true.  Using 1 vs -1 has been more my experience.

>
I got the impression that the manual/compiler prefer -1 over 1.
>
print not 0%
>
does print -1.

 
This sort of makes some sense when one considers the bit
representation of `-1` on a 2s complement machine (all bits 1).

>
True.
>
But there is no consistency between languages.
>
$ type dump.for
[snip]

I don't know why this should be surprising?

For Pascal, the integer values of `true` and `false` are given
in the standards documents (from e.g., ISO/IEC 7185:1990(E) sec
6.4.2.2. para (c): "The ordinal numbers of the truth values
denoted by *false* and *true* shall be the integer values 0 and
1 respectively."

In C, the relevant standards and most historical compilers treat
0 as false and anything non-zero as true and the negation
operator turns 0 into a 1 (I'm not sure how far back this goes).

Treating -1 as true in BASIC seems rather common, from the quick
survey I did; I speculate that this is almost certainly due to
the bit representation of -1 having all bits set, while in BASIC
the integer type is (usually?) signed, thus -1 on a two's
complement machine.  I wonder what the original DTSS BASIC did?

- Dan C.