Xcode Gives Strange Output From NSArray - iphone

Question

When I run this code, the output is some 1084848 to the console. I can't figure out why such odd output... here is the code.
#import <Foundation/Foundation.h>
int main (int argc, const char * argv[])
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
NSMutableArray *array = [[NSMutableArray alloc] init];
int someNumber = 3;
[array addObject:[NSNumber numberWithInt:someNumber]];
NSLog(#"%i" , [array objectAtIndex:0]);
[pool drain];
return 0;
}

Answer 1

the "%i" format specifier expects an integer, not an Object.
Try NSLog(#"%i" , [[array objectAtIndex:0] intValue]);
XCode is probably giving you a warning on this line: something like "Conversion specifies type 'int', but argument has type 'id'".

Answer 2

Here's the pseudocode of your program:
//
// Inside of your main function....
//
// Set up the Autorelease pool and then create an array
//
// Declare an int
//
// Add the int to an array, while wrapping it in an NSNumber
//
// Log the value of the first object in the array, using the int formatter
//
// Clean up and return
//
You are logging the first object in the array, but NSArray cannot hold a primitive that's not wrapped in an Objective-C object.
To better understand your code, try changing these lines of code:
int someNumber = 3;
[array addObject:[NSNumber numberWithInt:someNumber]];
Expand them a little. Try this:
int someNumber = 3;
NSNumber *aNumber = [NSNumber numberWithInt:someNumber];
[array addObject:aNumber];
So, you've correctly wrapped the int in an NSNumber, but you're not unwrapping it. You need to ask your NSNumber for the int that it holds like so:
[[array objectAtIndex:0] intValue];
Or, to do the logging in one line:
NSLog(#"%i" , [[array objectAtIndex:0] intValue]);
The characters "%i" is called a "formatter". Different kinds of values require different formatters. When you are using an Objective-C object, you use "%#". For an NSInteger or int, you'd use %i. For a float, you'd use "%f". The point is that you need to either unwrap that number, or use the Objective-C formatter for strings.
A quick note about that weird value you were getting earlier: That's a memory address in RAM. It's the closest thing you're going to get when you use an incorrect formatter. In some cases, using the wrong formatter will cause an EXC_BAD_ACCESS. You were "lucky" and got a weird value instead of a dead program. I suggest learning about strings and formatters before you move on. It will make your life a lot easier.

Answer 3

When you use %i for integer values then you should give arguments as integer as below
NSLog(#"%i" , [[array objectAtIndex:0] intValue]);
But when you want object to be displayed then you must use %# which identifies object in general case as below:
NSLog(#"%#", array);