iPhone: How do I convert a string with a currency symbol to a negative number ?

Question

Say I have a string which is £23.56 or $23.56 how can I convert it into -23.56 ?

I have this part

NSMutableString *strAmount = [NSMutableString stringWithString:txtAmount.text];
[strAmount replaceCharactersInRange: [strAmount rangeOfString: strCurrencySymbol]  withString:@""];

Answer 1

That looks like a good start. You could use rangeOfCharacterFromSet:instead of rangeOfString: though after creating a set of currency symbols. Your code could look like this:

NSMutableString *strAmount = [NSMutableString stringWithString:txtAmount.text];
NSCharacterSet *currencySet = [NSCharacterSet characterSetWithCharactersInString:@"$€£"];
[strAmount replaceCharactersInRange: [strAmount rangeOfCharacterFromSet:currencySet]  withString:@"-"];

Answer 2

Use NSNumberFormatter

NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
[formatter setNumberStyle:NSNumberFormatterCurrencyStyle];
[formatter setLenient:YES];

NSNumber *number = [formatter numberFromString:@"£23.56"];

NSDecimalNumber *minusOne = [NSDecimalNumber decimalNumberWithString:@"-1.00"];
NSDecimalNumber *money = [NSDecimalNumber decimalNumberWithDecimal:[number decimalValue]];
NSDecimalNumber *negativeMoney = [money decimalNumberByMultiplyingBy:minusOne];

NSLog(@"£23.56 is now %@", [negativeMoney description]);