bitwise not operator

Question

Why bitwise operation (~0); prints -1 ? In binary , not 0 should be 1 . why ?

Answer 1

~ is a bitwise operator.

~0 = 1 which is -1 in 2's complement form  

http://en.wikipedia.org/wiki/Two's_complement

Some numbers in two's complement form and their bit-wise not ~ (just below them):

0 1 1 1 1 1 1 1 = 127
1 0 0 0 0 0 0 0 = −128

0 1 1 1 1 1 1 0 = 126
1 0 0 0 0 0 0 1 = −127

1 1 1 1 1 1 1 1 = −1
0 0 0 0 0 0 0 0 = 0

1 1 1 1 1 1 1 0 = −2
0 0 0 0 0 0 0 1 = 1

1 0 0 0 0 0 0 1 = −127
0 1 1 1 1 1 1 0 = 126

1 0 0 0 0 0 0 0 = −128
0 1 1 1 1 1 1 1 = 127