a=5,b=2 a!=!!b What does the operation do?

Answer 1

In "C", a non zero integer is "true"(so a is true and b is also true) and the "!" operator is the NOT operator. Your second line reads as; a is NOT equal to (NOT NOT b) which is equivalent to; a is NOT equal to b (5 is not equal to 1) and the result is "true" (i.e one(1)).

In case you are confused, let me explain further:
b was originally 2 (which is true)
!b becomes false (i.e 0)
!!b becomes true (i.e 1)
a != !!b means 5 is not equal to 1....
and that statement is true (1)

Answer 2

Yes Calvin Thomas, that is a concise way of explaining it

Answer 3

Durga M I use '!!' to extract the boolean value from an int. It's like the bool() function in Python, except that the result is in the integer form.