Detect whether number is a float/integer?

IphoneSdk · August 2012

I need to detect whether a number entered by the user is an integer or a float. If the number is an integer, I will just round to 1dp however if it is a float, I will round to 3dp.

I know how to do the rounding, it's just detecting the integer/float in the first place that I'm stuck with.

Thanks

Brandt · August 2012

the variable that will hold the text should be declared as CGFloat or NSInteger. A CGFloat can hold an integer but will add the appropriate amount of zeros to it.

Duncan C · August 2012

There are a couple of different things you can do. You can look at the string input and see if it contains a decimal separator. (A "." in the US, a "," in many European countries, and I-don't-know-what elsewhere.)

To make that approach portable, you will need to figure out what the decimal separator character is in the current locale. I don't know how to do that off the top of my head, but there should be a way. After a brief search, it looks like you can query the current locale for it's kCFLocaleDecimalSeparator value using the method CFLocaleGetValue.

You can compare the value to it's rounded/truncated value:

if (input == truncf(input))
  //it's an integer
else
  //it's a float

RLScott · August 2012

Do you consider an entry of 5.0 to be a float or an int?

IphoneSdk · September 2012

Duncan C said:
There are a couple of different things you can do. You can look at the string input and see if it contains a decimal separator. (A "." in the US, a "," in many European countries, and I-don't-know-what elsewhere.)

To make that approach portable, you will need to figure out what the decimal separator character is in the current locale. I don't know how to do that off the top of my head, but there should be a way. After a brief search, it looks like you can query the current locale for it's kCFLocaleDecimalSeparator value using the method CFLocaleGetValue.

You can compare the value to it's rounded/truncated value:
if (input == truncf(input))
  //it's an integer
else
  //it's a float

Thanks, I'll give it a go.

IphoneSdk · September 2012

RLScott said:
Do you consider an entry of 5.0 to be a float or an int?

I want it to be considered an integer.

RLScott · September 2012

IphoneSdk said:

RLScott said:
Do you consider an entry of 5.0 to be a float or an int?
I want it to be considered an integer.

Then looking for decimal points in the string will do no good. But Duncan's second soution comparing the truncated value will work just fine, as long as the input has less than 8 significant figures. At more than about 8 significant figures the internal representation of a float looses some of the resolution, so that 987654321.01 may look like an int. But if you are not dealing with such big numbers, that solution will work just fine.

IphoneSdk · September 2012

Not a particularly elegant solution but it works!!

NSString *aString;
    NSString *string = @".";
    NSRange r = [aTextField.text rangeOfString:string];
    NSString *string1 = @",";
    NSRange s = [aTextField.text rangeOfString:string1];
    if (r.location != NSNotFound | s.location != NSNotFound) {
        NSLog(@"a Float");
        
        aString = [NSString stringWithFormat:@"%.1fx²", aInt];
    }
    else {
        NSLog(@"a Integer");
        
        aString = [NSString stringWithFormat:@"%.0fx²", aInt];
    }

baja_yu · September 2012

That's a bad solution. You can't be certain that the decimal separator will always be those two characters. If you want to go that route then look into NSLocaleDecimalSeparator. But the way Duncan showed you is not just more robust, it's also much more efficient. You're creating several objects and performing several string searches, whereas you could just do one truncf(), and instead of one line of code you have a dozen.

baja_yu · September 2012

And have you tried the %g format specifier (https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/Strings/Articles/formatSpecifiers.html)

NSLog(@"%.2g", 1.000000);
NSLog(@"%.2g", 1.123456789);

BrianSlick · September 2012

NSNumberFormatter provides a decimal separator that should be localized.

RLScott · September 2012

Forget about the decimal separator. Since the OP wants to count "5.0" as an int, you would have to check that there is nothing besides zeroes after the decimal point. Looking at the truncated value is the best (Duncan's second solution.)

baja_yu · September 2012

%g format specifier is even simpler, as, judging by his code, he just wants to show decimal places if they are not zero. %g will do that for him.

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Detect whether number is a float/integer?

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