Account.h

#ifndef ACCOUNT_H
#define ACCOUNT_H

#include <iostream>
using namespace std;

class Account
{
public:
	Account(double startBalance = 0.0)
	{
		if(startBalance < 0.0)
		{
			cout << "Starting balance is invalid." << endl;
		}

		if (startBalance > 0.0)
		{
			balance = startBalance;
		}
		else
		{
			balance = 0.0;
		}
	}

	virtual double getBalance()
	{
		return balance;
	}

	virtual void debit(double i = 0.0)
	{
		if(i > balance)
		{
			cout << "Debit amount exceeded account balance." << endl;
		}
		else
		{
			balance -= i;
		}
	}
	
	virtual void credit(double j = 0.0)
	{
		balance += j;
	}		

protected:
	double balance;
};

#endif

CheckingAccount.h

#include <iostream>
using namespace std;

#include "Account.h"

class CheckingAccount : public Account
{
public:
	CheckingAccount(double startBalance = 0.0, double startFee = 0.0)
	{
		if(startBalance < 0.0)
		{
			cout << "Starting balance is invalid." << endl;
		}

		if (startBalance > 0.0)
		{
			balance = startBalance;
		}
		else
		{
			balance = 0.0;
		}

		if (startFee > 0.0)
		{
			interestFee = startFee;
		}
		else
		{
			startFee = 0.0;
		}
	}
	
	void debit(double i = 0.0)
	{
		if(i > balance)
		{
			cout << "Debit amount exceeded balance." << endl;
		}
		else
		{
			balance  -= i + interestFee;
			cout << "Transaction fee charged: " << interestFee << "." << endl;
		}
	}

	void credit(double j = 0.0)
	{
		balance += j - interestFee;
		cout << "Transaction fee charged: " << interestFee << "." << endl;
	}

private:
	double interestFee;
};

Main.cpp

#include <iostream>
using std::cout;
using std::cin;
using std::endl;

#include <iomanip>
using std::setprecision;
using std::fixed;

#include <vector>
using std::vector;

#include "Account.h" // Account class definition
#include "SavingsAccount.h" // SavingsAccount class definition
#include "CheckingAccount.h" // CheckingAccount class definition

int main()
{
   // create vector accounts
   vector < Account * > accounts( 4 );   

   // initialize vector with Accounts
   accounts[ 0 ] = new SavingsAccount( 25.0, .03 ); 
   accounts[ 1 ] = new CheckingAccount( 80.0, 1.0 );
   accounts[ 2 ] = new SavingsAccount( 200.0, .015 ); 
   accounts[ 3 ] = new CheckingAccount( 400.0, .5 );

   cout << fixed << setprecision( 2 );

   // loop through vector, prompting user for debit and credit amounts
   for ( size_t i = 0; i < accounts.size(); i++ )
   {
      cout << "Account " << i + 1 << " balance: $" 
         << accounts[ i ]->getBalance();

      double withdrawalAmount = 0.0;
      cout << "\nEnter an amount to withdraw from Account " << i + 1 
         << ": ";
      cin >> withdrawalAmount;
      accounts[ i ]->debit( withdrawalAmount ); // attempt to debit

      double depositAmount = 0.0;
      cout << "Enter an amount to deposit into Account " << i + 1 
         << ": ";
      cin >> depositAmount;
      accounts[ i ]->credit( depositAmount ); // credit amount to Account

      // downcast pointer
      SavingsAccount *savingsAccountPtr =
         dynamic_cast < SavingsAccount * > ( accounts[ i ] );

      // if Account is a SavingsAccount, calculate and add interest
      if ( savingsAccountPtr != 0 )
      {
         double interestEarned = savingsAccountPtr->calculateInterest();
         cout << "Adding $" << interestEarned << " interest to Account "
            << i + 1 << " (a SavingsAccount)" << endl;
         savingsAccountPtr->credit( interestEarned );
      } // end if
      
      cout << "Updated Account " << i + 1 << " balance: $" 
         << accounts[ i ]->getBalance() << "\n\n";
   } // end for
   system("pause");
   return 0;
} // end main

SavingsAccount.h

#include <iostream>
using namespace std;

#include "Account.h"

class SavingsAccount : public Account
{
public:
	SavingsAccount(double startBalance = 0.0, double startRate = 0.0)
	{
		if(startBalance < 0.0)
		{
			cout << "Starting balance is invalid." << endl;
		}

		if (startBalance > 0.0)
		{
			balance = startBalance;
		}
		else
		{
			balance = 0.0;
		}

		if (startRate > 0.0)
		{
			interestRate = startRate;
		}
		else
		{
			startRate = 0.0;
		}

	}

	double calculateInterest()
	{
		double interest = interestRate * balance;
		return interest;
	}

private:
	double interestRate;
};