algorithm - Finding the number of digits of an integer

Question

What is the best method to find the number of digits of a positive integer?

I have found this 3 basic methods:

• conversion to string

  String s = new Integer(t).toString(); 
  int len = s.length();
  

• for loop

  for(long long int temp = number; temp >= 1;)
  {
      temp/=10;
      decimalPlaces++;
  } 
  

• logaritmic calculation

  digits = floor( log10( number ) ) + 1;
  

where you can calculate log10(x) = ln(x) / ln(10) in most languages.

First I thought the string method is the dirtiest one but the more I think about it the more I think it's the fastest way. Or is it?

Answer 1

There's always this method:

n = 1;
if ( i >= 100000000 ) { n += 8; i /= 100000000; }
if ( i >= 10000     ) { n += 4; i /= 10000; }
if ( i >= 100       ) { n += 2; i /= 100; }
if ( i >= 10        ) { n += 1; }