Assuming you are using Cocoa (or just Foundation), you can use NSNumberFormatter and set its style to currency:
NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
[formatter setNumberStyle:NSNumberFormatterCurrencyStyle];
... = [formatter stringFromNumber:number];
By default it uses the locale of your system, but you can change that and lots of other properties, see the NSNumberFormatter API docs.
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