First off, I wasn't sure where to post this because I didn't know if the -- is classified as a worksheet function or not, but what does it do? I've seen them in a bunch of posts. I am just curious what they do.

Example:

=SUMPRODUCT(--($D$1:$D$100="100"),$F$1:$F$100)

versus

=SUMPRODUCT(($D$1:$D$100="100"),$F$1:$F$100)

Why does the second one not work?

Thanks,
Nick