Sum of products of two arrays (dotproduct)

Question

First off, I know my title can be formulated better, but my math classes are so far gone I can\'t remember the correct words anymore..

I need to do something like this (

Answer 1

Very simply, do a loop.

int sum = 0;
for(int i = 0; i < digits1.length && i < digits2.length; i++)
{
    sum += digits1[i] * digits2[i];
}

Boom.