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

Question

This is a problem from Project Euler, and this question includes some source code, so consider this your spoiler alert, in case you are interested in solving it yourself. It

Answer 1

A solution without using the BigInteger class is to store each digit in it's own int and then do the multiplication manually.

static void Problem16()
{
    int[] digits = new int[350];

    //we're doing multiplication so start with a value of 1
    digits[0] = 1;
    //2^1000 so we'll be multiplying 1000 times
    for (int i = 0; i < 1000; i++)
    {
        //run down the entire array multiplying each digit by 2
        for (int j = digits.Length - 2; j >= 0; j--)
        {
            //multiply
            digits[j] *= 2;
            //carry
            digits[j + 1] += digits[j] / 10;
            //reduce
            digits[j] %= 10;
        }
    }

    //now just collect the result
    long result = 0;
    for (int i = 0; i < digits.Length; i++)
    {
        result += digits[i];
    }

    Console.WriteLine(result);
    Console.ReadKey();
}