// if x is empty:            1 - -1 == 2
// if x is zero:             1 - 0 - 1 == 0
// if x is any other number: 1 - x - 1 == x
#define ENABLED(x) (1 - x -1 != 0)


#if defined FLAG && ENABLED(FLAG)
// execute if FLAG is defined as not-zero
#endif

#include <stdio.h>

#define TEST1
#define TEST2 0
#define TEST3 1
// define TEST4 // not defined

#define ENABLED(x) (1 - x -1 != 0)

int main(void)
{

#if defined TEST1 && ENABLED(TEST1)
    printf("TEST1 is enabled!n");
#endif

#if defined TEST2 && ENABLED(TEST2)
    printf("TEST2 is disabled!n");
#endif

#if defined TEST3 && ENABLED(TEST3)
    printf("TEST3 is enabled!n");
#endif

#if defined TEST4 && ENABLED(TEST4)
    printf("TEST4 is disabled!n");
#endif

    return 0;
}