Base(x) { cout << "Middle(" << x << ")" << endl; } }; class Derived : public Middle { public: Derived(int x) : Middle(x) { cout << "Derived(" << x << ")" << endl; } }; int main() { Derived d(5); return 0; }28:T4d4,#include <iostream> using namespace std; class Base { public: virtual Base* clone() { cout << "Base clone" << endl; return new Base(*this); } virtual ~Base() {} }; class Derived : public Base { public: Derived* clone() override { cout << "Derived clone" << endl; return new Derived(*this); } }; int main() { Base* b = new Derived(); Base* c = b->clone(); delete c; delete b; return 0; }29:T424,#include <iostream> using namespace std; class Base final { public: void show() { cout << "Base class" << endl; } }; // class Derived : public Base {}; // Error: cannot inherit from final class class Animal { public: virtual void speak() final { cout << "..." << endl; } }; class Dog : public Animal { // void speak() override {} // Error: cannot override final function }; int main() { Base b; b.show(); Dog d; return 0; }2a:T4f3,#include <iostream> using namespace std; class Base { public: int x; Base() : x(10) {} virtual void show() { cout << "Base x=" << x << endl; } virtual ~Base() {} }; class Derived : public Base { public: int y; Derived() : y(20) {} void show() override { cout << "Derived x=" << x << " y=" << y << endl; } }; int main() { Derived d; Base b = d; // Slicing: Derived part is lost b.show

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