I have a facing vector instead of a facing angle. The plus side is you don't need to cos and sin constantly, only when they turn. Then when you want to move somebody you just do
movement=[facing scale:speed];
[position add:movement];

I just made up arbitrary function names but you can probably get the point.
When you want to turn all you need to do is rotate the facing vector by X radians negative for a left turn, positive for a right turn. You can rotate a vector using CGAffineTransform functions.