Fastest way to get number of digits on a number?

Question

I have do detect the amount of digits on a number. For example, 329586 has 6 digits.

What I done, is simply parsing the number to string, and getting the string length, like:

number.toString().length()

But, is there a fastest way to count digits on a number? I have to use this method several times, so I think using toString() can impact performance.

Thanks.

by number you mean an integer ? – Denys Séguret Mar 23 '13 at 14:24 — Denys Séguret, Mar 23 '13 at 14:24

Eng.Fouad · Accepted Answer · 2013-03-23T14:30:16.507

41

Math.floor(Math.log10(number) + 1)
// or just (int) Math.log10(number) + 1

For example:

int number = 123456;
int length = (int) Math.log10(number) + 1;
System.out.println(length);

OUTPUT:

edited Mar 23 '13 at 14:30

answered Mar 23 '13 at 14:24

Eng.Fouad

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That's not the fastest way, see the this answer: http://stackoverflow.com/questions/1306727/way-to-get-number-of-digits-in-an-int/1308407#1308407 – gaborsch Mar 23 '13 at 14:31
1

This method needs the number==0 case to be handled separately. – Patricia Shanahan Mar 23 '13 at 14:52
2

Yes, this does **not** work for zero! – mike Dec 22 '15 at 16:15
Although not the fastest or most general solution, it is very elegant! – Pavel Razgovorov Jun 23 '20 at 07:33

TravellingGeek · Answer 2 · 2013-03-23T14:36:48.870

10

how about this homebrewed solution:

int noOfDigit = 1;
while((n=n/10) != 0) ++noOfDigit;

edited Mar 23 '13 at 14:36

answered Mar 23 '13 at 14:29

TravellingGeek

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It worked too, thank you! :D – JoaaoVerona Mar 23 '13 at 14:30

Zelldon · Answer 3 · 2017-01-20T15:00:11.000

0

Try this :

Working Example

public class Main {
    public static void main(String[] args) {
        long num = -23;
        int digits = 0;
        if (num < 0) 
            num *= (-1);
        if (num < 10 && num >= 0)
            digits = 1;
        else {
            while(num > 0) {
                num /= 10;
                digits++;
            }
        }
        System.out.println("Digits: " +digits);
    }
}

edited Jan 20 '17 at 15:00

answered Mar 23 '13 at 14:31

Zelldon

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Thank you too! :D But, just saying, it won't work for 0 and 1... – JoaaoVerona Mar 23 '13 at 14:35
Now it will work for 0, 1 and also for negative numbers. – Zelldon Mar 23 '13 at 14:50
2

for 10, it would return 1! – Saeed Apr 10 '14 at 18:11
Sorry. Updated my answer. – Zelldon Jan 20 '17 at 15:01

Fastest way to get number of digits on a number?

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