Constructors and Destructors - General Questions

What will be the output of the program?

#include <iostream>
using namespace std;
class P {
public:
    int x;
    P(int v) : x(v) {}
    P(const P &o) : x(o.x + 1) { cout << "copy "; }
};
int main() {
    P a(5);
    P b = a;
    cout << b.x << endl;
    return 0;
}

Why should a base class with virtual functions have a virtual destructor?

When is a copy constructor called?

What will be the output of the program?

#include <iostream>
using namespace std;
class A {
public:
    A() { cout << "A"; }
    ~A() { cout << "a"; }
};
int main() {
    {
        A x;
    }
    cout << "M" << endl;
    return 0;
}

What will be the output of the program?

#include <iostream>
using namespace std;
class A {
    int id;
public:
    A(int i) : id(i) { cout << "C" << id; }
    ~A() { cout << "D" << id; }
};
int main() {
    A a(1);
    A b(2);
    return 0;
}