I'm using this code to invert an NSDecimalNumber for easier arithmetic:
self.thisTransaction.amount = [NSDecimalNumber decimalNumberWithString:self.amountField.text locale:NSLocale.currentLocale];
NSLog(@"1 thisTransaction.amount is %@",self.thisTransaction.amount);
// Inverts the transaction amount
// This code negates the number, but chops off the part on the right side of the decimal
self.thisTransaction.amount = [NSDecimalNumber decimalNumberWithMantissa:[self.thisTransaction.amount longLongValue] exponent:0 isNegative:YES];
NSLog(@"2 thisTransaction.amount is %@",self.thisTransaction.amount);
Well, I thought the arithmetic would be easier, anyway. However, as revealed in the console readout below, the code negates the number, but truncates the number at the decimal point and returns a whole integer instead of a decimal:
2015-05-27 10:07:30.767 XXXXX[11835:10266658] 1 thisTransaction.amount is 25.49
2015-05-27 10:07:39.735 XXXXX[11835:10266658] 2 thisTransaction.amount is -25
I've looked at quite a few posts on SO, but they seem to go around in circles. I'd sure appreciate some guidance.
EDIT:
Pursuant to @rmaddy's suggestion below, I changed the code as follows:
self.thisTransaction.amount = [NSDecimalNumber decimalNumberWithString:self.amountField.text locale:NSLocale.currentLocale];
NSLog(@"1 thisTransaction.amount is %@",self.thisTransaction.amount);
// Inverts the transaction amount
NSDecimalNumber * invertedMultiplier = [NSDecimalNumber decimalNumberWithString:@"-1"];
self.thisTransaction.amount = [self.thisTransaction.amount decimalNumberByMultiplyingBy:invertedMultiplier];
NSLog(@"2 thisTransaction.amount is %@",self.thisTransaction.amount);
This seems to work fine.
If you want to negate an NSDecimalNumber you can simply do:
NSDecimalNumber *originalNumber = ... // the original decimal number
NSDecimalNumber *negatedNumber = [originalNumber decimalNumberByMultiplyingBy:[NSDecimalNumber numberWithInt:-1]];
And for fun, here's another way:
NSDecimalNumber *anotherNegate = [[NSDecimalNumber zero] decimalNumberBySubtracting:originalNumber];