Here i made 2 different macros to calculate your absolute, the second one, is probably the most correct one and goes straight to the point.
#define ABSOLUTE_VALUE(x) if (x < 0) \
NSLog(@"Value is negative, converting: %i", -x); \
NSLog(@"Value is positive, remains: %i", x)
#define ABSOLUTE_VALUE2(x) (x < 0) ? -x : x
int main(int argc, const char * argv)
NSLog(@"Testing %i", ABSOLUTE_VALUE2(-5 * 2));
ABSOLUTE_VALUE(-5 * 2);