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Cocoala · Apr 3, 2002, 08:03 AM

How would i do simple calculations like this in Objective-C?

I have 2 NSNumber Objects containing number values and i want to add these in another field.

I guess i probably have to convert NSNumbers to int, but how?

Thanks in advance,
Cocoala

Detrius · Apr 3, 2002, 09:45 AM

Apple's Documentation on NSNumber

<BLOCKQUOTE>code:<HR><pre>
NSNumber *a,*b, *c;
a = [NSNumber alloc];
b = [NSNumber alloc];
c = [NSNumber alloc];
[a initWithInt: 1];
[b initWithInt: 1];
[c initWithInt: [a intValue] + [b intValue]];
[/code]

That would technically be how you would do what you requested purely with NSNumbers. you could also use the +numberWithInt: function on the NSNumber class instead of using alloc and init seperately:

<BLOCKQUOTE>code:<HR><pre>
a = [NSNumber numberWithInt: 1];
[/code]

That developer documentation comes in really handy sometimes. But in Objective-C, there is a much much easier way to do what you requested:

<BLOCKQUOTE>code:<HR><pre>
int a=1,b=1,c;
c=a+b;
[/code]

don't bother with NSNumbers to do that kind of stuff.

lindberg · Apr 3, 2002, 11:28 AM

I second the basic advice -- it's usually easier to work with scalar ints, floats, etc. NSNumber is useful as a wrapper when you need objects (to, say, put in an NSDictionary or something) but otherwise they're a bit of a pain. You'll notice that almost none of the AppKit APIs use NSNumbers -- they use unsigned, float, double, etc.

One note though on the example code -- don't split up the +alloc and -init calls like that. -init* methods are allowed to return different objects than the original receiver. NSNumber is a class cluster, so it's one example of where this happens -- it returns a specific subclass based on how you initialize it.

I.e do NOT do:
<BLOCKQUOTE>code:<HR><pre>
NSNumber *a;
a = [NSNumber alloc];
[a initWithInt: 1];
[/code]

At the very least do:
<BLOCKQUOTE>code:<HR><pre>
NSNumber *a;
a = [NSNumber alloc];
a = [a initWithInt: 1];
[/code]

or better:
<BLOCKQUOTE>code:<HR><pre>
NSNumber *a;
a = [[NSNumber alloc] initWithInt:1];
[/code];

As you say, [NSNumber numberWithInt:1] is also easy, and it is already autoreleased that way. When you use +alloc, you have to call either -release or -autorelease on it yourself.

Rickster · Apr 3, 2002, 09:33 PM

You don't want to do math with NSNumbers... just do it with plain C operators and primitive data types, unless you need something (like arbitrary precision or complex math) that C doesn't provide. NSNumbers are for the purpose of wrapping primitive-type values in objects for use with other code that expects to be dealing with objects (like storing them in an NSArray).