Question

For C programming, what does it mean when there is an exclamation mark after an equal sign? ie:

x=y;
y=!x;
x=!y;

Answer 1

http://en.wikipedia.org/wiki/Operators_in_C_and_C%2B%2B

! is the unary logical negation operator

So you've got assignment in the last two statements, where you're assigning a boolean (0 or 1) to y or x.

Answer 2

in statement
y = !x

Value of X will be inverted (0 --> 1 and vice versa) bit by bit, and will be copied in Y. For example,

!4 = 3