Most programming interfaces that deal with angles talk in radians (2 pi radians in a circle), like`CGAffineTransformRotate`

. I personally think better in degrees (360 degrees in a circle).Convert degrees to radians by multiplying by

`180 / pi`

.Convert radians to degrees by multiplying by

`pi / 180`

I have a couple of #defines I stick into a common header for projects that need it;

#define BWDegToRad(d) ((d) * M_PI / 180.0) #define BWRadToDeg(r) ((r) * 180 / M_PI)

Advanced Mac OS X Programming book

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