单选题库

void visit(TreeNode *root) {
    if (root == nullptr)
        return;
    visit(root->left);
    cout << root->val << " ";
    visit(root->right);
}

const int MAXN = 8;
int data[MAXN];
int front = 0, rear = 0;

bool full() {
    return  __________________________;
}

stack<int> s;
queue<int> q;
for (int i = 2; i <= 6; i += 2) {
    s.push(i);
    q.push(i);
}
s.pop();
q.pop();
cout << s.top() << " " << q.front();

class Base {
    public:
    Base() {
        cout << "B ";
    }
    virtual ~Base() {
        cout << "~B ";
    }
};

class Derived : public Base {
    public:
    Derived() {
        cout << "D ";
    }
    ~Derived() {
        cout << "~D ";
    }
};

int main() {
    Base *p = new Derived();
    delete p;
    return  0;
}

class Machine {
    protected:
    string id;

    public:
    Machine(string s) : id(s) {}
};

class Robot : public Machine {
    int level;

    public:
    Robot(string s, int n) : __________, level(n) {}
};