Adding multiple NSDecimalNumbers

Question

What's the best practice for doing this:

I have an array of NSDecimalNumbers and I need to add them all together.

I was going to set up a base number and then loop and add each subsequent number to the base...sort of like this:

 NSDecimalNumber* baseNumber = [[NSDecimalNumber alloc] initWithString:[NSString stringWithFormat:@"%f", 0.0]];

    for(int i=0; i<itemsToAdd.count; i++) {
        NSDecimalNumber* thisNumber = [itemsToAdd objectAtIndex:i];
        [baseNumber decimalNumberByAdding:thisNumber];
    }

NSLog(@"%@", baseNumber);

but I keep getting 0 for the total. I thought baseNumber would increment. Obviously not. : D Here's one of the batch of numbers I am working with, they total out to 81649.64.

2013-02-05 08:58:50.833 EUS Calculator[37430:c07] 4905.6
2013-02-05 08:58:50.834 EUS Calculator[37430:c07] 13850.88
2013-02-05 08:58:50.834 EUS Calculator[37430:c07] 43246.08
2013-02-05 08:58:50.835 EUS Calculator[37430:c07] 19944.96
2013-02-05 08:58:50.835 EUS Calculator[37430:c07] 412.8
2013-02-05 08:58:50.835 EUS Calculator[37430:c07] 289.92
2013-02-05 08:58:50.836 EUS Calculator[37430:c07] 0

How can I add a batch of NSDecimalNumbers? I will eventually convert these to currency strings.

Answer 1

NSDecimalNumber is an immutable class. That is, once constructed, an instance doesn't change. The message decimalNumberByAdding: returns a new number. As such, you'll need to record the new instance each time around. The following code should work.

NSDecimalNumber* baseNumber = [NSDecimalNumber zero];

for (int i = 0; i < itemsToAdd.count; i++)
{
    baseNumber = [baseNumber decimalNumberByAdding:[itemsToAdd objectAtIndex:i]];
}

NSLog(@"%@", baseNumber);

Remember to retain the baseNumber if you're not using ARC and want it to hang around beyond the next autorelease pool drain.