int N;
cout << "请输入整数：";
cin >> N;

bool Flag = false;

if (N >= 2) {
    Flag = true;
    for (int i = 2; i < N; i++)
        if (N % i == 0) {
            Flag = false;
            break;
        }
}

if (Flag)
    cout << "是质数";
else
    cout << "不是质数";