The first loop is allocating an object an initializing it with the
value of the loop variable (i) multiplied by 3.
The second loop is just assigning a pointer to that allocated object.
It could have also been written :
for (i = 0 i < 10; i++)
{
NSLog(@"The number at index %d is %@", i, [array objectAtIndex:i]);
}
that would get rid of the temporary variable and the author probably
wanted to allow you to step through the code in the debugger and see
the value retrieved from the array.
On May 19, 2008, at 8:18 PM, Brad Gibbs wrote:
On pages 36-7 of Aaron Hillegass' new book, he provides sample code
for a Foundation Tool called Lottery. The code is below:
NSMutableArray *array;
array = [[NSMutableArray alloc] init];
int i;
for (i = 0; i < 10; i++) {
NSNumber *newNumber = [[NSNumber alloc] initWithInt:(i * 3)];
[array addObject:newNumber];
}
for (i = 0; i < 10; i++) {
NSNumber *numberToPrint = [array objectAtIndex:i];
NSLog(@"The number at index %d is %@", i, numberToPrint);
}
He allocates memory for and initializes the first two objects, array
and newNumber. But, in the second 'for loop', numberToPrint is
neither allocated nor initialized, but the program compiles and runs
as expected. I replaced the second 'for loop' with the following,
just to see what would happen:
for (i = 0; i < 10; i++) {
NSNumber *numberToPrint;
numberToPrint = [[NSNumber alloc] init];
numberToPrint = [array objectAtIndex:i];
NSLog(@"The number at index %d is %@", i, numberToPrint);
}
It compiled and ran as expected, too. But, when I tried to
eliminate allocation and initialization for newNumber in the first
'for loop', the app threw an exception. I don't see an explanation
in the book re why numberToPrint can be, but doesn't need to be
allocated or initialized. Is it because numberToPrint is simply
pointing to newNumber objects in the array that have already been
allocated and initialized? Could someone please explain this?
Thank you.
Brad
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