Modulus Behavior -1 % 3 (C++)

Question

if (currIndex < 0) {

            cout << currIndex << " % " << array.size() << endl;

            currIndex = currIndex % array.size();

            cout << currIndex << endl;
}

Output:

-1 % 3
0

-1 % 3 = -1 in C++ so why is 0 being returned?

Full Snippet: https://ideone.com/leWqhi

Answer 1

size() returns unsigned integer type, so this computation is done by casting -1 to unsigned and performing unsigned modulo.

Cast size() to signed integer type to get correct result.