Polymorphism and Virtual Functions - General Questions

What will be the output of the program?

#include <iostream>
using namespace std;
class A { public: void f() { cout << "A"; } };
class B : public A { public: void f() { cout << "B"; } };
int main() {
    B b;
    A *p = &b;
    p->f();
    cout << endl;
    return 0;
}

What will be the output of the program?

#include <iostream>
using namespace std;
int area(int s) { return s * s; }
double area(double r) { return 3 * r * r; }
int main() {
    cout << area(2) << " " << area(2.0) << endl;
    return 0;
}

What will be the output of the program?

#include <iostream>
using namespace std;
class Shape { public: virtual const char* name() { return "shape"; } virtual ~Shape() {} };
class Circle : public Shape { public: const char* name() override { return "circle"; } };
int main() {
    Shape *s = new Circle();
    cout << s->name() << endl;
    delete s;
    return 0;
}

What does the override keyword do?

Can a constructor be virtual in C++?