What double negation does in C

Question

I had a controversy about what compilers \"think\" about this:

a = 8;
b = !!a;

So, is b == 0x01 ? Is TRUE always

Answer 1

You have not supplied enough information to tell whether !!a works for your purposes or not.

You stated that you really need the result of a > 0. However, this is not equivalent to !!a if a is signed and holds a negative value. If this is possible, then the answer is obviously "no".

!!a is equivalent to a != 0, not to a > 0.