If statement checking NSArray size

Question

I've an if statement, used to check if an indice is less than the end of the array. This is not working when the value of "i" is -1.

NSMutableArray *myArray = [NSMutableArray array];
[myArray addObject:@"coucou"];

int i = -1;

// Not working
if (i < ([myArray count] - 1) ){
    NSLog(@" first ok ");
}

// Fix
int count = [myArray count] - 1;
if ( i < count ){
    NSLog(@" second ok ");
}

This is what i need to do to get it working (same algorithm, but using an intermediate variable to store the size of the array) Anyone know why ?

because [myArray count] returns NSUInteger and you are compairing it with int variable. use (int)[myArray count]. It will work fine. — Yogendra, Jul 01 '14 at 09:31

score 3 · Accepted Answer · edited May 23 '17 at 10:28

3

[myArray count] return a NSUInteger which is an unsigned integer value.

When you compare an unsigned integer with an signed integer, the signed integer will be convert to unsigned, so the value i is not negative now.

Look here for more information.

edited May 23 '17 at 10:28

Community

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answered Jul 01 '14 at 09:40

KudoCC

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Yeah much closer to the truth. You should emphasize that by "not negative" you actually get "very large" during such conversions. – trojanfoe Jul 01 '14 at 09:41
Unsigned value is the 2's complement of the signed value. That's why for negative values it results in very large/small number like this: (2^32 - abs(your number)). The number of bits are machine architecture dependent. If your integer carries 4 byte then its 32 bit etc. – if-else-switch Jul 01 '14 at 09:50

score 0 · Answer 2 · answered Jul 01 '14 at 09:35

0

You are comparing a signed integer with int thats why it is happening use NSUInteger instead of int. It will definitely work

answered Jul 01 '14 at 09:35

Avinash Tag

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because when you are writing `if (i < ([myArray count] - 1) ){ NSLog(@" first ok "); } `([myArray count] - 1) gives you and unsigned integer and you are comparing it with int use expression [myArray count]-1 to debug you will get your answer – Avinash Tag Jul 01 '14 at 09:46

score 0 · Answer 3 · answered Jul 01 '14 at 09:39

0

[myArray count] it returns unsigned long value you need to keep either of these two

((NSInteger)[myArray count] - 1) OR ((int)[myArray count] - 1)

answered Jul 01 '14 at 09:39

Balu

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If statement checking NSArray size

3 Answers3