C++ Primer

Hi, I'm reading C++ Primer 4th Edition at the moment and have encountered something in the book which doesn't make sense to me, I don't know if I've interpreted it wrong or something but how does this equal 255:

"So, if we assign 1 to an 8-bit unsigned char, the resulting value will be 255, which is 1 modulo 256."

I don't seem to understand, wouldn't it be 1 since you've assigned it as 1? Sorry for asking such a stupid question. :p

I believe it should be -1.
Assign -1 to unsigned char and you get 255.

That's what I get for downloading a 'legit' version of the book. :p