Check if NSDecimalNumber is whole number

Question

What's the easiest way to check if an instance of NSDecimalNumber is a whole number?

Thanks!

Sekofski

I am not sure. What about if ([myDecNumber isEqualToNumber:[myDecNumber integerValue]])? – Diverticulum

Just cast your decimal value to int and check if its the same – Devilment

Maybe something like this: if ([myDecimalNumber decimalValue] / 1.0) > 0) {}? – Dogeatdog

Answer 1

@interface NSDecimalNumber (IsIntegerNumber)
@property (readonly) BOOL isIntegerNumber;
@end

@implementation NSDecimalNumber (IsIntegerNumber)
-(BOOL)isIntegerNumber {
    NSDecimalValue value = [self decimalValue];
    if (NSDecimalIsNotANumber(&value)) return NO;
    NSDecimal rounded;
    NSDecimalRound(&rounded, &value, 0, NSRoundPlain);
    return NSDecimalCompare(&rounded, &value) == NSOrderedSame;
}
@end

Dentoid

Answer 2

Subtract the whole number from the decimal number. If the difference is zero then the decimal number is a whole number.

// testVal is NSDecimalNumber
NSString *test = [testVal stringValue];
int intVal = [test intValue];
double doubleVal = [test doubleValue];
if(doubleVal-intVal == 0){
    NSLog(@"Whole number!");
}

Or, get the whole number and compare to the original value:

if(intVal == doubleVal){
    NSLog(@"Whole number!");
}

Kronick

I submitted an edit of the answer and changed one 'double' to 'int'. However, I think that the origial version would work fine as well. Sorry to bother you. – Diverticulum

Any method that use double cannot be used with NSDecimalNumber. What if the number has 30 digits? – Siesta

This is simpliest solution! – Olivia

Answer 3

This should work.

Beware of using methods that convert NSDecimalNumber into double.

NSDecimalNumber* input = [...];

NSDecimal roundedDecimal;
NSDecimalRound(&roundedDecimal, [input decimalValue], 0, NSRoundPlain);

NSDecimalNumber* roundedNumber = [NSDecimalNumber decimalNumberWithDecimal:roundedDecimal];

BOOL inputIsWholeNumber = [input isEqualToNumber:roundedNumber];

You should also check for NaN values.

Siesta

I haven't had the chance to test it out yet, but this seems to be the solution I'm looking for. Thank you. – Sekofski

@Sekofski Also check out Jody Hagins' answer. – Siesta

He/she submitted it right after accepted yours. I upvoted both, but I think changing the accepted answer to his/hers may be more helpful to others looking for a quick answer. Hope you don't mind. – Sekofski

Answer 4

Can you not use if ((number % 1) == 0)

Pitt

Answer 5

@implementation NSDecimalNumber (isWholeNumber)
-(BOOL)isWholeNumber
{
    double x = [self doubleValue]; //The approximate value of the receiver as a double.
    double y = floor (x);
    if(fabs(x - y) < DBL_EPSILON)
      return YES;
    return NO;
}
@end  
// [myDecNumber isWholeNumber];

Escarole

You lose precision. double cannot cover all the values from NSDecimalNumber. – Siesta

I was under the impression that a tiny bit of precision is lost when converting NSDecimalNumber to double or float. I could be mistaken about this, but I'm curious to know if the outcome of this approach would be affected if that were indeed the case. Thanks. – Sekofski

@Siesta Yes because double is base-2 while NSDecimalNumber is base-10. – Escarole

@Sekofski The loss caused by base-10 to base-2 conversion is significant but the important thing is that a NSDecimalNumber can hold up to 38 decimal digits while double ony about 16 decimal digits! – Siesta

Answer 6

Not sure why, but for some reason I was unable to get Jody Hagins' or Sulthan's solutions to work so I went a slightly different way:

-(BOOL)isWholeNumber:(NSDecimalNumber *)number {
    NSDecimalNumber *input = number;

    NSDecimalNumberHandler *handler = [NSDecimalNumberHandler decimalNumberHandlerWithRoundingMode:NSRoundPlain
                                                                                             scale:0
                                                                                  raiseOnExactness:NO
                                                                                   raiseOnOverflow:NO
                                                                                  raiseOnUnderflow:NO
                                                                               raiseOnDivideByZero:NO];

    NSDecimalNumber *vOne = [NSDecimalNumber decimalNumberWithString:@"1"];

    NSDecimalNumber *result = [number decimalNumberByMultiplyingBy:vOne
                                                      withBehavior:handler];

    BOOL inputIsWholeNumber = [input isEqualToNumber:result];

    return inputIsWholeNumber;
}

Odelsting

Answer 7

Try this, you can skip first line, i just used it to create a NSDecimalNumber object

NSDecimalNumber  *decNumb=[NSDecimalNumber decimalNumberWithString:@"20.5"];//try with just 20
NSString* str=[NSString stringWithFormat:@"%@",decNumb];

if ([str rangeOfString:@"."].location==NSNotFound && [str rangeOfString:@"-"].location==NSNotFound) {
    NSLog(@"it is whole number");
} 
else
    NSLog(@"it is not whole number");

Interceptor

Not really good for localization. And what if the number is "2.0" ? – Siesta

NSDecimalNumber automatically converts 20.0 to 20. Please check it your self – Interceptor

Can you check the above code by assigning 2.0 to decNumb. Somehow NSDecimalNumber seems to standardize 2.0 to 2. – Interceptor

Yes, it does that but it's undocumented behavior. – Siesta