Make sense yet? What's the final result? That's right. Add 270.
I know I'm replying to an old post but this answer is just wrong I think.
The original results would give if:
west=180 or -180
adding 270 gives:
west=450 or 90
the only result I can think of that would be usefull is:
north=0 or 360
east or west=270
east or west=90
edit: This gives the right answer if the original answer was "polar":
int nonPolar= 90-((polar+180)%360)