How to get the one's compliment and why it is just making it negative and just adding 1 on it?

Question

#include <stdio.h>

int main()

{

int a = 9, b;

b = ~a;

printf("The answer is %d.");

return 0;

}

OUTPUT:

The answer is -10.

Answer 1

Please, read ones' complement, and two's complement as well.

TL; DR; To get ones' complement you invert all the bits. This includes the sign bit (since your type is a signed int). That's why it will be negative. Also, negative numbers are represented as two's complement. But since two's complement = ones' complement + 1, your result will be one less than the original number with its sign flipped. (ones' complement = two's complement -1).

Check out this question as well.

Answer 2

when ever we use bit wise negation (~) one's complement . we can get out put by this formula = -(n+1) 

compiler will convert decimal form (9)  to binary form then we get ( 1001 ) and it will use two's complement (where it will add 1 to (1001) .then it becomes  1010 which is 10 in decimal form the out put will be in the form of negative

 

we get 10 in negative =-10