Question

(Account Inheritance Hierarchy) Create an inheritance hierarchy that a bank might use to represent customers' bank accounts. All customers at this bank can deposit (i.e., credit) money into their accounts and withdraw (i.e., debit) money from their accounts. More specific types of accounts also exist. Savings accounts, for instance, earn interest on the money they hold. Checking accounts, on the other hand, charge a fee per transaction (i.e.. credit or debit). Create an inheritance hierarchy containing base class account and derived classes savingsAccount and checkingAccount that inherit from class Account. Base class Account should include one data member of type double to represent the account balance. The class should provide a constructor that receives an initial balance and uses it to initialize the data member. The constructor should validate the initial balance to ensure that it is greater than or equal to \(\theta . \theta .\) If not, the balance should be set to \(\theta . \theta\) and the constructor should display an error message, indicating that the initial balance was invalid. The class should provide three member functions. Member function credit should add an amount to the current balance. Member function debit should withdraw money from the account and ensure that the debit amount does not exceed the account's balance. If it does, the balance should be left unchanged and the function should print the message "Debit amount exceeded account balance." Member function getBalance should return the current balance. Derived class savingsAccount should inherit the functionality of an Account, but also include a data member of type double indicating the interest rate (percentage) assigned to the Account. SavingsAccount's constructor should receive the initial balance, as well as an initial value for the SavingsAccount's interest rate. SavingsAccount should provide a public member function calculateInterest that returns a double indicating the amount of interest earned by an account. Member function calculateInterest should determine this amount by multiplying the interest rate by the account balance. [Note: SavingsAccount should inherit member functions credit and debit as is without redefining them.] Derived class checkingAccount should inherit from base class Account and include an additional data member of type double that represents the fee charged per transaction. CheckingAccount's constructor should receive the initial balance, as well as a parameter indicating a fee amount. Class CheckingAccount should redefine member functions credit and debit so that they subtract the fee from the account balance whenever either transaction is performed successfully. CheckingAccount's versions of these functions should invoke the base-class account version to perform the updates to an account balance. CheckingAccount's debit function should charge a fee only if money is actually withdrawn (i.e., the debit amount does not exceed the account balance). [Hint: Define Account's debit function so that it returns a bool indicating whether money was withdrawn. Then use the return value to determine whether a fee should be charged.] After defining the classes in this hierarchy, write a program that creates objects of each class and tests their member functions. Add interest to the SavingsAccount object by first invoking its calculateInterest function, then passing the returned interest amount to the object's credit function.

Short answer

Create the 'Account' class with balance handling, extend for 'SavingsAccount' with interest, and 'CheckingAccount' with fees, then test functionalities.

Step-by-step solution

Define the Base Class 'Account'

Start by defining a class named 'Account'. This class should encapsulate a single member variable for the account balance of type double. You will define a constructor to initialize the balance, ensuring the initial balance is non-negative. If the balance is negative, initialize it to 0.0 and print an error message. Additionally, implement member functions 'credit' to add money, 'debit' to withdraw money, ensuring no overdraft, and 'getBalance' to return the current balance.

Define the Derived Class 'SavingsAccount'

Inherit 'SavingsAccount' from the base class 'Account'. It should add a new member variable for the interest rate. Its constructor should accept an initial balance and interest rate, initializing the base class's balance and its own interest rate. Implement the 'calculateInterest' function, which calculates interest by multiplying the balance by the interest rate and returns it as a double.

Define the Derived Class 'CheckingAccount'

Define 'CheckingAccount' inheriting from 'Account'. Add a member variable to represent the transaction fee. In its constructor, accept parameters for the initial balance and transaction fee, passing the balance to the base class constructor. Override the 'credit' and 'debit' functions to deduct the transaction fee from the balance after a successful transaction. Ensure that 'debit' invokes the base class method and only applies the fee if the withdrawal was successful, using the bool approach.

Create and Test Class Objects

Using the defined classes, create objects for 'Account', 'SavingsAccount', and 'CheckingAccount'. Test each class by applying credits, debits, checking balances, and for 'SavingsAccount', calculating and applying interest. Validate that 'CheckingAccount' properly applies the transaction fee where intended, ensuring the correct functionality of all class methods.

Key concepts

Inheritance Hierarchy

Inheritance in Object-Oriented Programming allows new classes, called derived classes, to take on properties and behaviors of existing classes, known as base classes. In this exercise, we create an inheritance hierarchy starting with the base class `Account`. This base class contains common features for different types of accounts, such as balance handling.
Derived classes, `SavingsAccount` and `CheckingAccount`, inherit from `Account`. This means that they share the account balance management functionality, while also providing their unique behaviors.

• Inheritance enables code reusability, reducing repetition.
• It allows us to define common functionality in a single place, preventing errors.
• Yet, derived classes can extend and modify behaviors based on their specific requirements.

Understanding inheritance is essential, as it models real-world relationships efficiently while keeping your code clean.

Class Design

Class design is the art of creating a blueprint for objects. In this exercise, you create three classes: `Account`, `SavingsAccount`, and `CheckingAccount`. This design differentiates between general and specific behaviors.
The base class `Account` is designed to handle common functionalities like balance operations. It includes methods for crediting and debiting amounts and a constructor for setting the initial balance.

• This design keeps the core logic centralized, aiding maintainability and extensibility.
• Derived classes add special functionalities without altering the base class directly.
• Divide concerns by letting each class handle one aspect of the required functionality.

Good class design ensures that your code is efficient, easy to update, and aligned with real-world relationships.

Polymorphism

Polymorphism allows objects of different classes to be treated as objects of a common superclass. In this exercise, we see polymorphic behavior when both `SavingsAccount` and `CheckingAccount` are treated as `Account` objects.
Polymorphism is powerful because it allows for flexible code that can interact with different object types through a consistent interface.

• Even though `SavingsAccount` and `CheckingAccount` differ in functionality, they share the base interface inherited from `Account`.
• This means you can invoke methods like `credit` and `debit` on them uniformly.
• It also enables the use of dynamic binding, allowing derived classes to override base class methods and introduce specific functionality.

Through polymorphism, you can write more generic and reusable code pieces, reducing dependencies and increasing flexibility.

Member Functions

Member functions are methods that operate on the data contained within a class. For `Account`, `SavingsAccount`, and `CheckingAccount`, key member functions bring specific banking functionalities to life.
The base class `Account` provides essential member functions:

• `credit(double amount)`: Adds a specified amount to the account balance.
• `debit(double amount)`: Withdraws a specified amount if the balance allows; otherwise, prints a warning.
• `getBalance()`: Returns the current account balance.

Each derived class can enhance or override these functions. For example:

• `SavingsAccount` introduces `calculateInterest()`, which computes interest based on the current balance and interest rate.
• `CheckingAccount` modifies `credit` and `debit` to include transaction fees.

The use of member functions allows for organized and encapsulated handling of account operations, making the system robust and clear in its functioning.