Is !x equal to true when x is negative?

Question

int main() {
    
    int x = -1;
                    
    if (!x) {
        printf("Yes\n");
                
    }
}

Is !x true when x is a negative number or it's true when it's only 0?

Answer 1

For any non-zero x, !x will be zero. So, for x == -1, !x is false.

From cppreference:

The logical NOT operator has type int. Its value is ​0​ if expression evaluates to a value that compares unequal to zero. Its value is 1 if expression evaluates to a value that compares equal to zero.

Answer 2

Any non-zero value is true even if it is negative value(e.g. -1 is true). So, negation of true is false. In the case of x=-1, if (x) will be evaluated to true. Thus, if(!x) will be false, and the printf("Yes\n"); will never be executed.