Bitwise NOT operator returning unexpected and negative value? [duplicate]

Answer 1

And want to check every bit if it's 1 or 0.

To check an individual bit, you don't NOT the number, you AND it with an appropriate bit mask:

if ((x & 1) != 0) ... // bit 0 is 1
if ((x & 2) != 0) ... // bit 1 is 1
if ((x & 4) != 0) ... // bit 2 is 1
if ((x & 8) != 0) ... // bit 3 is 1
...
if ((x & (1 << n)) != 0) ... // bit n is 1
...
if ((x & 0x80000000) != 0) ... // bit 31 is 1