c++ - Operator !! producing unexpected result

Question

I have a problem relative to some C++ code about the !! operator. It gives me an unexpected result and I don't understand why:

int x=-12; 
x=!!x; 
print("value=",x);

The output of this is 1. But i do not know how. Can anyone explain this ambiguous result?

Answer 1

!!x is grouped as !(!x).

!x is 0 if x is non-zero, and 1 if x is zero.

Applying ! to that reverses the result.

So, !!x can be viewed as a way of setting x to 1 if it's not zero, and remaining at 0 if it's zero. In other words x = !!x is the same as x = x ? 1 : 0.