Convert NSDecimalNumbers to Negative

Working on a budget app in swift.

Essentially, there is a label that displays keypad textInput to currencyStyle and displays this number ($5.00), then waits for user to choose Debit or Withdraw. If debit, number is appended to Table, but I'm lost when it comes to Withdraw(-).

I would like to

1. Convert NSDecimalNumber which is formatted as currency to a negative for appending to a tableView: String ($5.00 to -$5.00).

2. Convert NSDecimalNumber value to a negative and add to an NSNumber array that is storing numbers to be calculated for an available balance (5.50 to -5.50)

For both I have tried using NSNumberFormatter negativePrefix and a few other properties in Apple Documentation to no avail. Even tried creating a negative NSNumber value = -100.0, but app crashed during division.

Any help would be appreciated.

To easily negate the NSDecimalNumber create an extension in Swift like this:

extension NSDecimalNumber {
    func negative() -> NSDecimalNumber {
        return self.decimalNumberByMultiplyingBy(NSDecimalNumber(mantissa: 1, exponent: 0, isNegative: true));
    }
}

You can then just negate your NSDecimalNumber like this:

yourNumber = yourNumber.negative()