~0 value

Question

I got the following question :
What is the value of x ?
x = 1 - (-1 == ~0)

The answer was 0.
I don't understand why the 1's complement (if "~" is 1's complement) of 0 is -1, what notion I've missed to understand this question ?

Thanks for constructive answers.

Answer 1

0 in eight bits is 00000000 and when you inverted it become 11111111 since the msb is the sign and when its 1 then the number is negative so
-128+64+32+16+8+4+2+1 which equal - 1
and as a rule ~var=-(var+1)