如何找到数字的不同数字之和？

Question

I'm trying to solve Project Euler #16:

2^15 = 32768 and the sum of its digits is 3 + 2 + 7 + 6 + 8 = 26.

What is the sum of the digits of the number 2^1000?

question looks simple but Instead of using modulus 10 I tried to solve the question like this:

public class Main {

    public static void main(String[] args) {


      long number = (long) Math.pow(2,100);

      long sum=0;

      String number2 = String.valueOf(number);

      char[] digits = number2.toCharArray();

      for (char digit : digits) {

        sum = sum + digit;
      }

      System.out.println(sum);



    }


}

However it gives a wrong answer, I can't see my mistake, Isn't it possible to solve this question with this way?

Answer 1

A long cannot hold the number. You must rewrite using a datatype that can.

See Large Numbers in Java for pointers.