ios - wrong boolean result within if statement -


this code should print false console print true

nsmutablearray *data = [[nsmutablearray alloc]init];  uilabel *label = [[uilabel alloc] init]; label.tag = 7;  if(label.tag <= (data.count - 1)) {     nslog(@"true"); } else {     nslog(@"false"); }

anyone can explain this?

data.count 0 unsigned integer (nsuinteger).

(data.count - 1) 0 - 1 in case won't equal -1 because integer unsigned. maximum integer (4294967295). call integer underflow.

you can fix 

label.tag + 1 <= data.count

with unsigned integer, have take care subtraction. way fix using cast signed integer:

label.tag <= ((nsinteger) data.count) - 1

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