How to use NSDecimalNumber?

Question

I\'m building a app that needs to perform calculations on money.

I wonder how to properly use NSDecimalNumber, especially how to initialize it from integers, floats

Answer 1

Design-wise, you should try to avoid converting NSDecimalNumber or NSDecimals to and from int, float, and double values for the same reasons it's recommended you use NSDecimalNumbers: loss of precision and binary floating point representation issues. I know, sometimes it's unavoidable (taking input from a slider, doing trigonometric calculations, etc.), but you should try to take input from users as NSStrings and then use initWithString:locale: or decimalNumberWithString:locale: to generate the NSDecimalNumbers. Do all your math with the NSDecimalNumbers and return their representation to users or save them to SQLite (or wherever) as their string description using descriptionWithLocale:.

If you have to input from an int, float, or double, you could do something like the following:

int myInt = 3;
NSDecimalNumber *newDecimal = [NSDecimalNumber decimalNumberWithString:[NSString stringWithFormat:@"%d", myInt]];

or you could follow Ashley's suggestion to make sure you're safe in the decimal construction.