double negation in C : is it guaranteed to return 0/1?
c, standards
Solution
Yes, in C99, see §6.5.3.3/4:
The result of the logical negation operator ! is 0 if the value of its operand compares unequal to 0, 1 if the value of its operand compares equal to 0. The result has type int. The expression !E is equivalent to (0==E).
So `!x` and `!!y` can only yield 0 or 1, as `int`s.
For other operators, in C99, see also Is the "true" result of >, <, !, &&, || or == defined?
Problem
Is `!!(x)` guaranteed by the standard to return 0/1? Note that I am not asking about c++, where a bool type is defined.