- Example

#include <iostream>
class Account{
public:
  Account(double amt): balance(amt){}
  virtual void withdraw(double amt){
    balance -= amt;
  }
  double getBalance() const {
    return balance;
  }
protected:
  double balance;
};
class BankAccount: public Account{
public:
  BankAccount(double amt): Account(amt){}
  virtual void withdraw(double amt){
    if ((balance - amt) > 0.0) balance -= amt;
  }
};
int main(){
  std::cout << std::endl;
  BankAccount bankAccount(100.0);
  Account * aPtr = &bankAccount;
  aPtr->withdraw(50);
  std::cout << "aPtr->getBalance(): " << aPtr->getBalance() << std::endl;
  std::cout << std::endl;
  BankAccount * bankAccount2 = new BankAccount(100.0);
  Account * aPtr2 = bankAccount2;
  aPtr2->withdraw(50);
  std::cout << "aPtr2->getBalance(): " << aPtr2->getBalance() << std::endl;
  std::cout << std::endl;
  BankAccount bankAccount3(100.0);
  Account& aRef = bankAccount3;
  aRef.withdraw(50);
  std::cout << "aRef.getBalance(): " << aRef.getBalance() << std::endl;
  std::cout << std::endl;
}