Check if NSDecimalNumber is whole number

Question

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

Thanks!

I am not sure. What about `if ([myDecNumber isEqualToNumber:[myDecNumber integerValue]])`? — Hermann Klecker, Sep 06 '12 at 11:14
Just cast your decimal value to int and check if its the same — muffe, Sep 06 '12 at 11:15
Maybe something like this: `if ([myDecimalNumber decimalValue] / 1.0) > 0) {}`? — woz, Sep 06 '12 at 11:17

score 10 · Accepted Answer · answered Sep 06 '12 at 17:07

@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

score 3 · Answer 2 · edited Sep 06 '12 at 11:45

3

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!");
}

edited Sep 06 '12 at 11:45

Hermann Klecker

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answered Sep 06 '12 at 11:30

yoninja

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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. – Hermann Klecker Sep 06 '12 at 11:47
Any method that use `double` cannot be used with `NSDecimalNumber`. What if the number has 30 digits? – Sulthan Sep 06 '12 at 13:04
This is simpliest solution! – Stefan Jul 16 '15 at 07:37

Sulthan · Answer 3 · 2012-09-06T17:57:15.977

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.

edited Sep 06 '12 at 17:57

answered Sep 06 '12 at 13:53

Sulthan

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I haven't had the chance to test it out yet, but this seems to be the solution I'm looking for. Thank you. – James Sep 07 '12 at 10:33
@James Also check out Jody Hagins' answer. – Sulthan Sep 07 '12 at 10:37
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. – James Sep 07 '12 at 10:40

score 0 · Answer 4 · answered Sep 06 '12 at 11:51

0

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

answered Sep 06 '12 at 11:51

Darren

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Parag Bafna · Answer 5 · 2012-09-06T13:07:56.790

0

@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];

edited Sep 06 '12 at 13:07

answered Sep 06 '12 at 11:52

Parag Bafna

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You lose precision. `double` cannot cover all the values from `NSDecimalNumber`. – Sulthan Sep 06 '12 at 13:04
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. – James Sep 06 '12 at 13:05
@Sulthan Yes because double is base-2 while NSDecimalNumber is base-10. – Parag Bafna Sep 06 '12 at 13:22
1

@James 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! – Sulthan Sep 06 '12 at 13:28

score 0 · Answer 6 · answered Aug 10 '14 at 03:13

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;
}

Neo · Answer 7 · 2012-09-06T11:32:06.697

-3

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");

edited Sep 06 '12 at 11:32

answered Sep 06 '12 at 11:24

Neo

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Not really good for localization. And what if the number is "2.0" ? – Sulthan Sep 06 '12 at 11:26
NSDecimalNumber automatically converts 20.0 to 20. Please check it your self – Neo Sep 06 '12 at 11:27
Can you check the above code by assigning 2.0 to decNumb. Somehow NSDecimalNumber seems to standardize 2.0 to 2. – Neo Sep 06 '12 at 11:30
Yes, it does that but it's undocumented behavior. – Sulthan Sep 06 '12 at 11:33

Check if NSDecimalNumber is whole number

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