Why do enum permissions often have 0, 1, 2, 4 values?

Question

Why are people always using enum values like 0, 1, 2, 4, 8 and not 0, 1, 2, 3, 4?

Has this something to do with bit operations, etc.?

Answer 1

Lot's of good answers to this one… I'll just say.. if you do not like, or cannot easily grasp what the << syntax is trying to express.. I personally prefer an alternative (and dare I say, straightforward enum declaration style)…

typedef NS_OPTIONS(NSUInteger, Align) {
    AlignLeft         = 00000001,
    AlignRight        = 00000010,
    AlignTop          = 00000100,
    AlignBottom       = 00001000,
    AlignTopLeft      = 00000101,
    AlignTopRight     = 00000110,
    AlignBottomLeft   = 00001001,
    AlignBottomRight  = 00001010
};

NSLog(@"%ld == %ld", AlignLeft | AlignBottom, AlignBottomLeft);

LOG 513 == 513

So much easier (for myself, at least) to comprehend. Line up the ones… describe the result you desire, get the result you WANT.. No "calculations" necessary.