Suppose I have two long longs, a and b, that I need to multiply, then get the value mod k for some large k, such that a, b, and k are all in the range of long long but not of int. For simplicity, a, b < k.
Thus the code would be:
long long a, b, k; cin >> a >> b >> k; cout << (a * b)%k << "\n";
However, since a and b are so large, if you multiply like above, and it overflows and becomes negative, then mod k would be a negative number and incorrect.
How can you ensure that the value mod k is correct?
Edit: As a bonus, how does this work in Java? Is it the same, as expected? Or is BigInteger needed?