The bit operations {~, &, |, ^} in C operate on integers at each bit of the integer.

So the DeMorgan's Identities just verified for single bit operands still hold for integers:

If x and y are C integers then

          ~(x & y) = (~x) | (~y)

          ~(x | y) = (~x) & (~y)

          ~~x = x
     

Example with 8 bit integers x and y

Verifying that ~(x & y) = (~x) | (~y)

x	0110 0011
y	1101 0111
x & y	0100 0011
~x	1001 1100
~y	0010 1000
(~x) | (~y)	1011 1100
~(x & y)	1011 1100