Why are the return values of these doubles -1.#IND?

Question

I have :

double score = cvMatchContourTrees( CT1, CT2, CV_CONTOUR_TREES_MATCH_I1, 0.0 );
        cout<

There are v

Answer 1

std::cout << (0/0.f);
// Output: -1.#IND

It's NaN.