How to add an integer to an array?

Question

This must be quite basic, but I was wondering how to add an integer to an array?

I know I can add strings like this:

NSMutableArray *trArray = [[NSMutableArray alloc] init];
[trArray addObject:@"0"];
[trArray addObject:@"1"];
[trArray addObject:@"2"];
[trArray addObject:@"3"];

But I guess I can't simply add integers like so:

NSMutableArray *trArray = [[NSMutableArray alloc] init];
[trArray addObject:0];
[trArray addObject:1];
[trArray addObject:2];
[trArray addObject:3];

At least the compiler isn't happy with that and tells me that I'm doing a cast without having told it so.

Any explanations would be very much appreciated.

Sandro Meier · Accepted Answer · 2014-01-03 12:46:37Z

29

Yes that's right. The compiler won't accept your code like this. The difference is the following:

If you write @"a String", it's the same as if you created a string and autoreleased it. So you create an object by using @"a String".

But an array can only store objects (more precise: pointers to object). So you have to create objects which store your integer.

NSNumber *anumber = [NSNumber numberWithInteger:4];
[yourArray addObject:anumber];

To retrive the integer again, do it like this

NSNumber anumber = [yourArray objectAtIndex:6];
int yourInteger = [anumber intValue];

I hope my answer helps you to understand why it doesn't work. You can't cast an integer to a pointer. And that is the warning you get from Xcode.

EDIT:

It is now also possible to write the following

[yourArray addObject:@3];

which is a shortcut to create a NSNumber. The same syntax is available for arrays

@[@1, @2];

will give you an NSArray containing 2 NSNumber objects with the values 1 and 2.

edited Jan 3, 2014 at 12:46

user529758

answered Apr 29, 2011 at 20:51

Sandro Meier

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6 Comments

n.evermind Over a year ago

Thanks, I think I understand this now. Your explanation is very good!

Sandro Meier Over a year ago

Thank you. The answer of mservidio is absolutly correct. But I always like to have an explanation. ;-)

n.evermind Over a year ago

Just a follow-up question: Is 'number' stored in my array an integer (int) or an NSInteger? Or doesn't this really matter?

Sandro Meier Over a year ago

As far as I know the difference is only a difference in the size which is used to store that value. I normally use int. The only reason for me: it's less to write. ;-) Perhaps there's someone around here who can explain the differnce. I can't.

user529758 Over a year ago

This is wrong, string literals aren't autoreleased. They have static storage duration and the highest possible reference count (which indicates that their refcount can't even be decreased by release).

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mservidio · Accepted Answer · 2011-04-29 20:46:01Z

7

You have to use NSNumbers I think, try adding these objects to your array: [NSNumber numberWithInteger:myInt];

NSMutableArray *trArray = [[NSMutableArray alloc] init];     
NSNumber *yourNumber = [[NSNumber alloc] numberWithInt:5];

[trArray addObject: yourNumber];

answered Apr 29, 2011 at 20:46

mservidio

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2 Comments

dredful Over a year ago

mservidio is correct. I believe the way to think of this is because @"2" is a NSString object. However 2 by itself is a value, not an object.

Jesse Naugher Over a year ago

to expand, you basically create an instance of the NSNumber object that is a object version of the primitive int or whatever and then adds this object to the array. Also, to get the primitive value back out of the array, use [[myArray objectAtIndex:0] intValue];

William A · Accepted Answer · 2011-04-29 21:02:53Z

4

You can also use this if you want to use strings:

NSMutableArray *array = [[NSMutableArray alloc] init];
[array addObject:[NSString stringWithFormat:@"%d",1]];
[[array objectAtIndex:0] intValue];

answered Apr 29, 2011 at 21:02

William A

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