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# ~0 value

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.

1 Answer

+ 2

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)