Yes/No values 0 and -1

[gee21]

I've been reading up on Access for a while now and am still baffled about something that is starting to bug me.


It is clear to me that in a Yes/No field, the value is equivalent to 0 when false - this part makes sense to me, but I don't understand why a true value is equivalent to -1 (instead of 1). In other words, why -1 as opposed to 1. Hope this post makes sense.

[ssanfu]

I've been reading up on Access for a while now and am still baffled about something that is starting to bug me.
It is clear to me that in a Yes/No field, the value is equivalent to 0 when false - this part makes sense to me, but I don't understand why a true value is equivalent to -1 (instead of 1). In other words, why -1 as opposed to 1. Hope this post makes sense.

It is kind of strange that in Access TRUE = -1, while in Excel, TRUE = 1.

IIRC, (and this was a long time ago) if you take zero and invert it (NOT 0), it becomes -1. Has something to do with bit wise shifts/ registers in the processor.

Look at it this way. Zero = FALSE. So far, so good.
If you then say TRUE = NOT FALSE, ANY number other than zero equals TRUE!

Try making a table with several integer fields. Add a couple of records. Enter zeros is a few, positive numbers (large and small) in a few and negative numbers (large and small).

Then create a form with the fields and add an equal number of check boxes bound to the fields. Only the check boxes that are zero will be unchecked. All others will be checked!