Problem 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?

#include <stdio.h>
int main()
{
    char st[500] = {0};
    int sum = 0;
    int i,j,k;
    st[0]=2;
    j = 0;
    for(i=1;i<1000;i++)
    {
        for(k=0;k<j+1;k++)
        {
            st[k]<<=1;  //每一位 x 2
        }
        for(k=0;k<j+1;k++)  //进位
        {
            st[k+1]+=st[k]/10;
            st[k] = st[k]%10;
        }
        if(st[j+1]) j++;  //有进位，再加一位
    }
    for(j;j>=0;j--)
    {
        sum+=st[j];
    }
    printf("%d",sum);
    return 0;
}