for (int i = 0; i < 100; i++) {
    std::cout << "Math's score' " << i+1 << ": ";
    std::cin >> scores[i];
    if(scores[i]<0)
    break;

    sum += scores[i];
}

student.set_scores(scores);
float average_ball = sum / 5.0;

int n=0;

for (int i = 0; i < n; i++) {

int n = 100;

if(n<0)
    break;

std::cin >> scores[i];

if (scores[i] < 0)
    break;