# Problem 15

$2^{15} = 32768$ and the sum of its digits is $3 + 2 + 7 + 6 + 8 = 26$.What is the sum of the digits of the number $2^{1000}$?

I had to write minimal code after adding a sumDigits method to my BigInt class. Since my class does not have a multiplication function yet I just did slow addition multiplication inline.

```
BigInt P15 (int target)
{
BigInt two = 2;
int n = 2;
while (n <= target)
{
two += two;
n++;
}
return two.sumDigits();
}
```

```
BigInt BigInt::sumDigits()
{
BigInt sum = 0;
for (int i = 0; i < this->length; i++)
sum += (this->number[i] - '0');
return sum;
}
```