c++ virtual

# include <iostream>
# include <vector>
using namespace std;
class Animal
{
public:
	virtual void eat() const { cout << "I eat like a generic Animal." << endl; }
	virtual ~Animal() {}
};
class Wolf : public Animal
{
public:
	void eat() const { cout << "I eat like a wolf!" << endl; }
};
class Fish : public Animal
{
public:
	void eat() const { cout << "I eat like a fish!" << endl; }
};
class GoldFish : public Fish
{
public:
	void eat() const { cout << "I eat like a goldfish!" << endl; }
};
class OtherAnimal : public Animal
{
};
int main()
{
	std::vector<Animal*> animals;
	animals.push_back( new Animal() );
	animals.push_back( new Wolf() );
	animals.push_back( new Fish() );
	animals.push_back( new GoldFish() );
	animals.push_back( new OtherAnimal() );
	for(auto it = animals.begin(); it != animals.end(); ++it) {
		(*it)->eat();
		delete *it;
	}
	return 0;
}
#include <iostream>
using namespace std;
class Account {
public:
	Account( double d ) {
		_balance = d;
	}
	virtual double GetBalance() {
		return _balance;
	}
	virtual void PrintBalance() {
		cerr << "Error. Balance not available for base type." << endl;
	}
private:
	double _balance;
};
class CheckingAccount : public Account {
public:
	CheckingAccount(double d) : Account(d) {}
       void PrintBalance() {
		cout << "Checking account balance: " << GetBalance() << endl;
	}
};
class SavingsAccount : public Account {
public:
 	SavingsAccount(double d) : Account(d) {}
    void PrintBalance() {
		cout << "Savings account balance: " << GetBalance() << endl;
	}
};
int main() {
    CheckingAccount *pChecking = new CheckingAccount( 100.00 ) ;
    SavingsAccount  *pSavings  = new SavingsAccount( 1000.00 );
    Account *pAccount = pChecking;
    pAccount->PrintBalance();
    pAccount = pSavings;
    pAccount->PrintBalance();
}