Fair, I forgot that C bools are just 0 and 1. That's where I first learned the !! trick, but it's been many a year.

Err, C bools have two interpreted values, TRUE, and FALSE.

Confusingly (to some) they are integers and while 0 represents FALSE, any non 0 value represents TRUE.

It's pedantic, apologies, but that is why the GP refers to "convert to strict boolean"