iOS：更正NSDecimalNumber计算

Question

First time using NSDecimalNumber, so I've wondered do I really need to create so many objects? In my method I want to calculate monthly costs out of daily costs. The monthly costs are stored in self.sumPerMonth and the parameter costs is the daily cost value. So I want to add to my monthly costs 30 * costs . Is this the easiest way to do that?

[self.sumPerMonth decimalNumberByAdding:[costs decimalNumberByMultiplyingBy:[NSDecimalNumber decimalNumberWithString:@"30"]]];

Answer 1

NSDecimalNumber is immutable so yes, you need to create a new object each time you do an operation.

The clumsiness of dealing with the objects is the compromise you make for getting base-10 calculations without loss of precision and with predictable rounding behavior .

Beware of mixing NSNumber and NSDecimalNumber .

A little reading: http://rypress.com/tutorials/objective-c/data-types/nsdecimalnumber.html

Answer 2

Yes, that's the way to go using NSDecimalNumber .

If there's valid reason to be concerned about number of objects created you could switch to the plain NSDecimal struct type. The difference is that NSDecimal is mutable.