#define IS_FOREIGNER(x) (!(x->citizen))
#define IS_SPOUSE(x) (x->married)
#define INCOME(x) (x->income)

...

int is_average( struct Person *person ) {
    if ( !IS_FOREIGNER( person ) && !IS_SPOUSE( person ) && INCOME( person ) > 3000 ) {
        return 1;
    } else {
        return 0;
    }
}