Question

hi am working with NSArrays using foundation tool and i have wrote the following code

    -(void)simplearrays
{
 NSMutableArray *arr = [NSMutableArray arrayWithCapacity:3];

 for(int i =0;i<3;i++)
 {
  scanf("%d",&arr[i]);
 }
 for(int j =0; j<3;j++)
 {
  printf("\n%d",arr[j]);
 }
}

My query is that the above code when executed shows the given output but the i get an error once the application finishes execution which says that “can’t allocate region” can you please help.

Also i wanted to know the difference between NSArray and NSMutable Array in icode blog i have read that nsarray can dynamically resize so if NSArray can dynamically resize then why to use NSMutable array or a better one would be when to use NSArray and when to use NSMutable Array???

Answer 1

Cocoa arrays are not C arrays. They are container objects with some similarities to Java vectors and array lists.

You cannot add objects or retrieve them using the C subscript syntax, you need to send messages to the object.

-(void)simplearrays
{
    NSMutableArray *arr = [NSMutableArray array]; 
    // arrayWithCapacity: just gives a hint as to how big the array might become.  It always starts out as
    // size 0.

    for(int i =0;i<3;i++)
    {
        int input;
        scanf("%d",&input);
        [array addObject: [NSNumber numberWithInt: input]];
        // You can't add primitive C types to an NSMutableArray.  You need to box them
        // with an Objective-C object
    }
    for(int j =0; j<3;j++)
    {
       printf("\n%d", [[arr objectAtIndex: j] intValue]);
       // Similarly you need to unbox C types when you retrieve them
    }
    // An alternative to the above loop is to use fast enumeration.  This will be
    // faster because you effectively 'batch up' the accesses to the elements
    for (NSNumber* aNumber in arr)
    {
       printf("\n%d", [aNumber intValue]);
    }
}