Update a class with properties and methods

Classes use properties and methods to encapsulate data and behavior. Properties define the data that a class contains, and methods define the behavior that the class performs.

In this exercise, you update an existing code project by developing properties and methods.

This exercise takes approximately 35 minutes to complete.

Before you start

Before you can start this exercise, you need to:

  1. Ensure that you have the latest short term support (STS) version of the .NET SDK installed on your computer. You can download the latest versions of the .NET SDK using the following URL: Download .NET
  2. Ensure that you have Visual Studio Code installed on your computer. You can download Visual Studio Code using the following URL: Download Visual Studio Code
  3. Ensure that you have the C# Dev Kit configured in Visual Studio Code.

For additional help configuring the Visual Studio Code environment, see Install and configure Visual Studio Code for C# development

Exercise scenario

Suppose you’re helping a non-profit company with a software project. You’ve decided to sharpen your object-oriented programming skills by creating a simple banking app. You’ve developed an initial version of the app that includes the following files:

  • BankCustomer.cs: The BankCustomer class includes fields for first name, last name, and customer ID. The class also includes constructors that initialize the fields.
  • BankAccount.cs: The BankAccount class includes fields for account number, balance, interest rate, account type, and customer ID. The class also includes constructors that initialize the fields.
  • Program.cs: The Program.cs file includes code that creates instances of the BankCustomer and BankAccount classes and demonstrates how each class is used.

This exercise includes the following tasks:

  1. Review the current version of your banking app
  2. Create properties for the BankCustomer class
  3. Create automatically implemented properties for the BankAccount class
  4. Create read-only properties for the BankAccount class
  5. Create methods for the BankCustomer and BankAccount classes
  6. Create extension methods for the BankCustomer and BankAccount classes
  7. Update the Program.cs file to demonstrate the updated classes, properties, and methods

Review the current version of your banking app

In this task, you download the existing version of your banking app and review the code.

Use the following steps to complete this section of the exercise:

  1. Download the starter code from the following URL: Implement classes, properties, and methods - exercise code projects

  2. Extract the contents of the LP1SampleApps.zip file to a folder location on your computer.

  3. Expand the LP1SampleApps folder, and then open the Classes_M2 folder.

    The Classes_M2 folder contains the following code project folders:

    • Solution
    • Starter

    The Starter folder contains the starter project files for this exercise.

  4. Use Visual Studio Code to open the Starter folder.

  5. In the EXPLORER view, collapse the STARTER folder, select SOLUTION EXPLORER, and expand the Classes_M2 project.

    You should see the following project files:

    • BankAccount.cs
    • BankCustomer.cs
    • Program.cs

  6. Open the BankCustomer.cs file.

  7. Take a minute to review the BankCustomer class.

    
 using System;
    
 namespace Classes_M2;
    
 public class BankCustomer
 {
     private static int s_nextCustomerId;
     public string FirstName = "Tim";
     public string LastName = "Shao";
     public readonly string CustomerId;
    
     static BankCustomer()
     {
         Random random = new Random();
         s_nextCustomerId = random.Next(10000000, 20000000);
     }
    
     public BankCustomer(string firstName, string lastName)
     {
         FirstName = firstName;
         LastName = lastName;
         this.CustomerId = (s_nextCustomerId++).ToString("D10");
     }
        
 }

    The BankCustomer class includes fields for FirstName, LastName, CustomerId, and a static field s_nextCustomerId. The s_nextCustomerId field is used to generate a unique customer ID for each customer.

    The BankCustomer class also includes two constructors. The first constructor is a static constructor that initializes the s_nextCustomerId field with a random number eight-digit integer. The second constructor takes two parameters, firstName and lastName, and initializes the FirstName and LastName fields with the values of the parameters. The constructor also increments s_nextCustomerId and uses the incremented value to assign a unique value to CustomerId.

    [!NOTE] The this keyword refers to the current instance of the class. It’s used to access fields, properties, and methods of the current instance. In the BankCustomer class, the this keyword is used to access the read-only CustomerId field. The this keyword is not required in this context, but it’s used for clarity. The this keyword is not available in a static constructor.

  8. Open the BankAccount.cs file.

  9. Take a minute to review the BankAccount class.

    
 using System;
    
 namespace Classes_M2;
    
 public class BankAccount
 {
     private static int s_nextAccountNumber;
     public readonly int AccountNumber;
     public double Balance = 0;
     public static double InterestRate;
     public string AccountType = "Checking";
     public readonly string CustomerId;
    
     static BankAccount()
     {
         Random random = new Random();
         s_nextAccountNumber = random.Next(10000000, 20000000);
         InterestRate = 0;
     }
    
     public BankAccount(string customerIdNumber)
     {
         this.AccountNumber = s_nextAccountNumber++;
         this.CustomerId = customerIdNumber;
     }
    
     public BankAccount(string customerIdNumber, double balance, string accountType)
     {
         this.AccountNumber = s_nextAccountNumber++;
         this.CustomerId = customerIdNumber;
         this.Balance = balance;
         this.AccountType = accountType;
     }
 }

    The BankAccount class includes fields for AccountNumber, Balance, InterestRate, AccountType, and CustomerId. The AccountNumber field is read-only and is initialized in the instance constructors. The Balance field is read-write and can be changed at any time. The AccountType field is read-write and can be changed at any time. The CustomerId field is read-only and is initialized in the instance constructors. The BankAccount class also has a static field s_nextAccountNumber which is used to generate unique account numbers for each new account. This field is initialized in a static constructor, which is called only once when the class is first loaded. The static constructor uses the Random class to generate a random starting value for s_nextAccountNumber. Additionally, the static constructor initializes the static field InterestRate to 0.

    The class also includes two instance constructors. The first instance constructor takes a single parameter, customerIdNumber, and initializes the AccountNumber and CustomerId fields. The second instance constructor takes three parameters: customerIdNumber, balance, and accountType. This constructor initializes the AccountNumber, CustomerId, Balance, and AccountType fields based on the provided values. Both constructors increment the s_nextAccountNumber to ensure that each new account has a unique account number. The static constructor initializes the s_nextAccountNumber and InterestRate fields.

  10. Open the Program.cs file.

  11. Take a minute to review the code.

    
 using Classes_M2;
    
 string firstName = "Tim";
 string lastName = "Shao";
    
 BankCustomer customer1 = new BankCustomer(firstName, lastName);
    
 firstName = "Lisa";
 BankCustomer customer2 = new BankCustomer(firstName, lastName);
    
 firstName = "Sandy";
 lastName = "Zoeng";
 BankCustomer customer3 = new BankCustomer(firstName, lastName);
    
 Console.WriteLine($"BankCustomer 1: {customer1.FirstName} {customer1.LastName} {customer1.CustomerId}");
 Console.WriteLine($"BankCustomer 2: {customer2.FirstName} {customer2.LastName} {customer2.CustomerId}");
 Console.WriteLine($"BankCustomer 3: {customer3.FirstName} {customer3.LastName} {customer3.CustomerId}");
    
 // Create accounts for customers
 BankAccount account1 = new BankAccount(customer1.CustomerId);
 BankAccount account2 = new BankAccount(customer2.CustomerId, 1500, "Checking");
 BankAccount account3 = new BankAccount(customer3.CustomerId, 2500, "Checking");
    
 Console.WriteLine($"Account 1: Account # {account1.AccountNumber}, type {account1.AccountType}, balance {account1.Balance}, rate {BankAccount.InterestRate}, customer ID {account1.CustomerId}");
 Console.WriteLine($"Account 2: Account # {account2.AccountNumber}, type {account2.AccountType}, balance {account2.Balance}, rate {BankAccount.InterestRate}, customer ID {account2.CustomerId}");
 Console.WriteLine($"Account 3: Account # {account3.AccountNumber}, type {account3.AccountType}, balance {account3.Balance}, rate {BankAccount.InterestRate}, customer ID {account3.CustomerId}");

    Your console app uses top-level statements as an implicit entry point for the app (rather than using a Main method). The code in Program.cs demonstrates how to create and use BankCustomer and BankAccount objects. the code initializes customer details, creates three BankCustomer objects, and prints their information. Then, it creates three BankAccount objects for these customers, specifying different balances and account types, and prints the account details, including account number, type, balance, interest rate, and customer ID.

  12. Run the app and review the output in the terminal window.

    Your app should produce output that’s similar to the following example:

    
 BankCustomer 1: Tim Shao 0014653176
 BankCustomer 2: Lisa Shao 0014653177
 BankCustomer 3: Sandy Zoeng 0014653178
 Account 1: Account # 12885967, type Checking, balance 0, rate 0, customer ID 0014653176
 Account 2: Account # 12885968, type Checking, balance 1500, rate 0, customer ID 0014653177
 Account 3: Account # 12885969, type Checking, balance 2500, rate 0, customer ID 0014653178

    The customer IDs and account numbers in your output will be different from the example output. Remember that they’re sequential values based on a randomly generated initial value.

    [!TIP] To run your app, right-click the Classes_M2 project in the Solution Explorer, select Debug, and then select Start New Instance. If you don’t see the Debug option listed, ensure that you’ve selected the Classes_M2 project in the Solution Explorer. The Debug option isn’t available when the Classes_M2 solution is selected.

Implement properties for the BankCustomer class

Properties are used to encapsulate data and provide controlled access to the fields of a class. Properties use property accessors to read (get) and write (set) the values of fields. In C#, properties are defined using the get and set accessors.

In this task, you create FirstName and LastName properties for the BankCustomer class using get and set property accessors. The get and set accessors provide controlled access to the private fields FirstName and LastName. You also update the Program.cs file to use the new properties.

Use the following steps to complete this section of the exercise:

  1. Open the BankCustomer.cs file.

  2. Locate the FirstName and LastName fields in the BankCustomer class:

    
 public string FirstName = "Tim";
 public string LastName = "Shao";

  3. To change the fields from public to private, update the FirstName and LastName fields to the following code:

    
 private string _firstName = "Tim";
 private string _lastName = "Shao";

    The _firstName and _lastName fields are now private, meaning they can only be accessed from within the BankCustomer class. This is a common practice in object-oriented programming to encapsulate data and prevent direct access to fields from outside the class.

  4. To create a FirstName property that accesses the private _firstName field, add the following code below the field declarations in the BankCustomer class:

    
 public string FirstName
 {
     get { return _firstName; }
     set { _firstName = value; }
 }

    The FirstName property is used to encapsulate the private field _firstName and provides controlled access to it.

    The public keyword indicates that the FirstName property is accessible from outside the class, meaning other classes and code can read and modify this property. The property is of type string, which means it holds text data.

    The property has two accessors: get and set. The get accessor is used to retrieve the value of the private field _firstName. When the property is accessed, the get accessor returns the current value of _firstName.

    The set accessor is used to assign a new value to the private field _firstName. The keyword value represents the value being assigned to the property. When a new value is assigned to FirstName, the set accessor sets _firstName to this new value.

  5. To create a LastName property that accesses the private _lastName field, add the following code to the BankCustomer class:

    
 public string LastName
 {
     get { return _lastName; }
     set { _lastName = value; }
 }

    The LastName property works the same way as the FirstName property. It encapsulates the private field _lastName and provides controlled access to it.

  6. Open the Program.cs file.

  7. Locate the following code statements:

    
 Console.WriteLine($"BankCustomer 1: {customer1.FirstName} {customer1.LastName} {customer1.CustomerId}");
 Console.WriteLine($"BankCustomer 2: {customer2.FirstName} {customer2.LastName} {customer2.CustomerId}");
 Console.WriteLine($"BankCustomer 3: {customer3.FirstName} {customer3.LastName} {customer3.CustomerId}");
    
 // Create accounts for customers
 BankAccount account1 = new BankAccount(customer1.CustomerId);
 BankAccount account2 = new BankAccount(customer2.CustomerId, 1500, "Checking");
 BankAccount account3 = new BankAccount(customer3.CustomerId, 2500, "Checking");

  8. To demonstrate the new BankCustomer properties, replace the code statements identified in the previous step with the following code snippet:

    
 Console.WriteLine($"BankCustomer 1: {customer1.FirstName} {customer1.LastName} {customer1.CustomerId}");
 Console.WriteLine($"BankCustomer 2: {customer2.FirstName} {customer2.LastName} {customer2.CustomerId}");
 Console.WriteLine($"BankCustomer 3: {customer3.FirstName} {customer3.LastName} {customer3.CustomerId}");
    
 // Create accounts for customers
 BankAccount account1 = new BankAccount(customer1.CustomerId);
 BankAccount account2 = new BankAccount(customer2.CustomerId, 1500, "Checking");
 BankAccount account3 = new BankAccount(customer3.CustomerId, 2500, "Checking");
    
 // Demonstrate the use of BankCustomer properties
 customer1.FirstName = "Thomas";
 customer1.LastName = "Margand";
 // customer1.CustomerId = "1234567890"; // This line will not compile
    
 Console.WriteLine($"Updated BankCustomer 1: {customer1.FirstName} {customer1.LastName} {customer1.CustomerId}");

    Notice that your code now uses the FirstName and LastName properties of the BankCustomer class to access the first name and last name of each customer. The code uses customer1 to demonstrate changing a customer’s first and last name, and then displays the updated customer data.

    You may also notice the commented code line that assigns a value to the CustomerId field directly. The CustomerId field is read-only and cannot be changed after it’s initialized in the constructor. If you uncomment this code line, your app won’t compile.

  9. Take a minute to review your code.

    BankCustomer.cs

    
 public class BankCustomer
 {
     private static int s_nextCustomerId;
     private string _firstName = "Tim";
     private string _lastName = "Shao";
     public readonly string CustomerId;
    
     public string FirstName
     {
         get { return _firstName; }
         set { _firstName = value; }
     }
    
     public string LastName
     {
         get { return _lastName; }
         set { _lastName = value; }
     }
    
     static BankCustomer()
     {
         Random random = new Random();
         s_nextCustomerId = random.Next(10000000, 20000000);
     }
    
     public BankCustomer(string firstName, string lastName)
     {
         FirstName = firstName;
         LastName = lastName;
         this.CustomerId = (s_nextCustomerId++).ToString("D10");
     }
 }

    Program.cs

    
 string firstName = "Tim";
 string lastName = "Shao";
    
 BankCustomer customer1 = new BankCustomer(firstName, lastName);
    
 firstName = "Lisa";
 BankCustomer customer2 = new BankCustomer(firstName, lastName);
    
 firstName = "Sandy";
 lastName = "Zoeng";
 BankCustomer customer3 = new BankCustomer(firstName, lastName);
    
 Console.WriteLine($"BankCustomer 1: {customer1.FirstName} {customer1.LastName} {customer1.CustomerId}");
 Console.WriteLine($"BankCustomer 2: {customer2.FirstName} {customer2.LastName} {customer2.CustomerId}");
 Console.WriteLine($"BankCustomer 3: {customer3.FirstName} {customer3.LastName} {customer3.CustomerId}");
    
 // Create accounts for customers
 BankAccount account1 = new BankAccount(customer1.CustomerId);
 BankAccount account2 = new BankAccount(customer2.CustomerId, 1500, "Checking");
 BankAccount account3 = new BankAccount(customer3.CustomerId, 2500, "Checking");
    
 // Demonstrate the use of BankCustomer properties
 customer1.FirstName = "Thomas";
 customer1.LastName = "Margand";
 // customer1.CustomerId = "1234567890"; // This line will not compile
    
 Console.WriteLine($"Updated BankCustomer 1: {customer1.FirstName} {customer1.LastName} {customer1.CustomerId}");
    
 Console.WriteLine($"Account 1: Account # {account1.AccountNumber}, type {account1.AccountType}, balance {account1.Balance}, rate {BankAccount.InterestRate}, customer ID {account1.CustomerId}");
 Console.WriteLine($"Account 2: Account # {account2.AccountNumber}, type {account2.AccountType}, balance {account2.Balance}, rate {BankAccount.InterestRate}, customer ID {account2.CustomerId}");
 Console.WriteLine($"Account 3: Account # {account3.AccountNumber}, type {account3.AccountType}, balance {account3.Balance}, rate {BankAccount.InterestRate}, customer ID {account3.CustomerId}");

  10. Run the app and review the output in the terminal window.

    Your app should produce output that’s similar to the following example:

    
 BankCustomer 1: Tim Shao 0010448234
 BankCustomer 2: Lisa Shao 0010448235
 BankCustomer 3: Sandy Zoeng 0010448236
 Updated BankCustomer 1: Thomas Margand 0010448234
 Account 1: Account # 16005571, type Checking, balance 0, rate 0, customer ID 0010448234
 Account 2: Account # 16005572, type Checking, balance 1500, rate 0, customer ID 0010448235
 Account 3: Account # 16005573, type Checking, balance 2500, rate 0, customer ID 0010448236

Create automatically implemented properties for the BankAccount class

Automatically implemented properties provide a simplified syntax for defining properties in C#. They automatically create a private, anonymous backing field that stores the property value. This allows you to define properties without explicitly defining the private fields that store the property values.

In this task, you create automatically implemented properties for the BankAccount class.

Use the following steps to complete this section of the exercise:

  1. Open the BankAccount.cs file.

  2. Notice that the BankAccount class has two public read-write fields: Balance and AccountType.

    • Balance is a read-write field that can be changed at any time.
    • AccountType is a read-write field that can be changed at any time.

    The other fields in the BankAccount class are either static or read-only:

    • AccountNumber is a read-only field that is set in the constructor and cannot be changed after that.
    • CustomerId is a read-only field that is set in the constructor and cannot be changed after that.
    • InterestRate is a static field that is shared among all instances of the BankAccount class.
    • s_nextAccountNumber is a static field that is shared among all instances of the BankAccount class.

  3. To convert the Balance and AccountType fields to automatically implemented properties, replace the Balance and AccountType field declarations with the following code:

    
 public double Balance { get; set; } = 0;
 public string AccountType { get; set; } = "Checking";

    The Balance and AccountType properties are automatically implemented properties that encapsulate anonymous backing fields that store the property values. The anonymous backing fields (_balance and _accountType) are created automatically by the C# compiler, so they’re not explicitly defined in the code.

    The public keyword indicates that the properties are accessible from outside the class, meaning other classes and code can read and write property values.

    The properties have two accessors: get and set. The get accessor is used to retrieve the value of the private field. When the property is accessed, the get accessor returns the current value of the private field.

    The set accessor is used to assign a new value to the private field. The value keyword represents the value being assigned to the property. When a new value is assigned to the property, the set accessor assigns value to the private field.

    [!NOTE] Your code doesn’t need to explicitly define the anonymous backing fields (_balance and _accountType) for auto-implemented properties. The C# compiler automatically creates these fields for you when using auto-implemented properties.

  4. Notice that the final constructor is now assigning values to the Balance and AccountType properties.

    Your updated constructor uses the balance and accountType parameters to assign values to the Balance and AccountType properties.

  5. Open the Program.cs file.

  6. Locate the Console.WriteLine statements that display the account information.

    
 Console.WriteLine($"Account 1: Account # {account1.AccountNumber}, type {account1.AccountType}, balance {account1.Balance}, rate {BankAccount.InterestRate}, customer ID {account1.CustomerId}");
 Console.WriteLine($"Account 2: Account # {account2.AccountNumber}, type {account2.AccountType}, balance {account2.Balance}, rate {BankAccount.InterestRate}, customer ID {account2.CustomerId}");
 Console.WriteLine($"Account 3: Account # {account3.AccountNumber}, type {account3.AccountType}, balance {account3.Balance}, rate {BankAccount.InterestRate}, customer ID {account3.CustomerId}");

    Notice that your code uses the Balance and AccountType properties of the BankAccount class to access the balance and account type of each account.

  7. Take a minute to review your code.

    BankAccount.cs

    
 public class BankAccount
 {
     private static int s_nextAccountNumber;
     public readonly int AccountNumber;
     public static double InterestRate;
     public readonly string CustomerId;
        
     public double Balance { get; set; } = 0;
     public string AccountType { get; set; } = "Checking";
    
     static BankAccount()
     {
         Random random = new Random();
         s_nextAccountNumber = random.Next(10000000, 20000000);
         InterestRate = 0;
     }
    
     public BankAccount(string customerIdNumber)
     {
         this.AccountNumber = s_nextAccountNumber++;
         this.CustomerId = customerIdNumber;
     }
    
     public BankAccount(string customerIdNumber, double balance, string accountType)
     {
         this.AccountNumber = s_nextAccountNumber++;
         this.CustomerId = customerIdNumber;

         this.Balance = balance;
         this.AccountType = accountType;
     }
 }

    Program.cs

    
 using Classes_M2;
    
 string firstName = "Tim";
 string lastName = "Shao";
    
 BankCustomer customer1 = new BankCustomer(firstName, lastName);
    
 firstName = "Lisa";
 BankCustomer customer2 = new BankCustomer(firstName, lastName);
    
 firstName = "Sandy";
 lastName = "Zoeng";
 BankCustomer customer3 = new BankCustomer(firstName, lastName);
    
 Console.WriteLine($"BankCustomer 1: {customer1.FirstName} {customer1.LastName} {customer1.CustomerId}");
 Console.WriteLine($"BankCustomer 2: {customer2.FirstName} {customer2.LastName} {customer2.CustomerId}");
 Console.WriteLine($"BankCustomer 3: {customer3.FirstName} {customer3.LastName} {customer3.CustomerId}");
    
 // Create accounts for customers
 BankAccount account1 = new BankAccount(customer1.CustomerId);
 BankAccount account2 = new BankAccount(customer2.CustomerId, 1500, "Checking");
 BankAccount account3 = new BankAccount(customer3.CustomerId, 2500, "Checking");
    
 // Demonstrate the use of BankCustomer properties
 customer1.FirstName = "Thomas";
 customer1.LastName = "Margand";
 // customer1.CustomerId = "1234567890"; // This line will not compile
    
 Console.WriteLine($"Updated BankCustomer 1: {customer1.FirstName} {customer1.LastName} {customer1.CustomerId}");
    
 Console.WriteLine($"Account 1: Account # {account1.AccountNumber}, type {account1.AccountType}, balance {account1.Balance}, rate {BankAccount.InterestRate}, customer ID {account1.CustomerId}");
 Console.WriteLine($"Account 2: Account # {account2.AccountNumber}, type {account2.AccountType}, balance {account2.Balance}, rate {BankAccount.InterestRate}, customer ID {account2.CustomerId}");
 Console.WriteLine($"Account 3: Account # {account3.AccountNumber}, type {account3.AccountType}, balance {account3.Balance}, rate {BankAccount.InterestRate}, customer ID {account3.CustomerId}");

  8. Run the app and review the output in the terminal window.

    Your app should produce output that’s similar to the following example:

    
 BankCustomer 1: Tim Shao 0014416130
 BankCustomer 2: Lisa Shao 0014416131
 BankCustomer 3: Sandy Zoeng 0014416132
 Updated BankCustomer 1: Thomas Margand 0014416130
 Account 1: Account # 13328120, type Checking, balance 0, rate 0, customer ID 0014416130
 Account 2: Account # 13328121, type Checking, balance 1500, rate 0, customer ID 0014416131
 Account 3: Account # 13328122, type Checking, balance 2500, rate 0, customer ID 0014416132

Create read-only properties for the BankAccount class

Read-only properties provide controlled access to the fields of a class by allowing the values of the properties to be read but not modified. Read-only properties are useful for ensuring that the state of an object remains consistent and can’t be changed after the object is constructed.

In this task, you create read-only properties in the BankAccount class.

Use the following steps to complete this section of the exercise:

  1. Open the BankAccount.cs file.

  2. Locate the two read-only fields: AccountNumber and CustomerId.

    
 public readonly int AccountNumber;
 public readonly string CustomerId;

    The read-only fields AccountNumber and CustomerId are both initialized in the constructors. The AccountNumber field is initialized with a unique value, and the CustomerId field is initialized with the value of the customerIdNumber parameter.

  3. To convert the AccountNumber and CustomerId fields to read-only properties, replace the AccountNumber and CustomerId field declarations with the following code:

    
 public int AccountNumber { get; }
 public string CustomerId { get; }

    The { get; } syntax indicates that these properties are read-only, meaning they can be accessed (read) but not updated (written) after the object is constructed. This is useful for ensuring that the account number and customer ID remain constant once they are set.

    Read-only properties provide a level of immutability (the object’s state can’t be modified after it’s created) and help to protect the integrity of the account data.

    Backing fields are not required for read-only properties because the C# compiler automatically creates them for you. The { get; } syntax tells the compiler to create an anonymous backing field to store the property value.

  4. Notice that the two instance constructors are now assigning values to the AccountNumber and CustomerId properties:

    
 public BankAccount(string customerIdNumber)
 {
     this.AccountNumber = s_nextAccountNumber++;
     this.CustomerId = customerIdNumber;
 }

 public BankAccount(string customerIdNumber, double balance, string accountType)
 {
     this.AccountNumber = s_nextAccountNumber++;
     this.CustomerId = customerIdNumber;
     this.Balance = balance;
     this.AccountType = accountType;
 }

    The instance constructors use the properties to assign values to the private backing fields.

  5. Open the Program.cs file.

  6. Notice that the Console.WriteLine statements using properties to display the data for the bank account objects.

    
 Console.WriteLine($"Account 1: Account # {account1.AccountNumber}, type {account1.AccountType}, balance {account1.Balance}, rate {BankAccount.InterestRate}, customer ID {account1.CustomerId}");
 Console.WriteLine($"Account 2: Account # {account2.AccountNumber}, type {account2.AccountType}, balance {account2.Balance}, rate {BankAccount.InterestRate}, customer ID {account2.CustomerId}");
 Console.WriteLine($"Account 3: Account # {account3.AccountNumber}, type {account3.AccountType}, balance {account3.Balance}, rate {BankAccount.InterestRate}, customer ID {account3.CustomerId}");

    The InterestRate field is accessed using the BankAccount class because it’s a static (and public) field.

  7. Run the app and review the output in the terminal window.

    Your app should produce output that’s similar to the following example:

    
 BankCustomer 1: Tim Shao 0010453163
 BankCustomer 2: Lisa Shao 0010453164
 BankCustomer 3: Sandy Zoeng 0010453165
 Updated BankCustomer 1: Thomas Margand 0010453163
 Account 1: Account # 15760425, type Checking, balance 0, rate 0, customer ID 0010453163
 Account 2: Account # 15760426, type Checking, balance 1500, rate 0, customer ID 0010453164
 Account 3: Account # 15760427, type Checking, balance 2500, rate 0, customer ID 0010453165

Create methods for the BankCustomer and BankAccount classes

Methods are used to define the behavior of a class. They encapsulate the logic that operates on the data stored in the class fields.

In this task, you create methods for the BankCustomer and BankAccount classes.

Use the following steps to complete this section of the exercise:

  1. Open the BankCustomer.cs file.

    The BankCustomer class has two properties: FirstName and LastName. You can create methods that perform operations on these properties. For example, you can create a method to return the full name of the customer by combining the first and last names. You can also create methods to update the customer’s name and display customer information.

  2. Create a blank code line below the final constructor.

  3. To create a method that returns the full name of the customer, add the following code:

    
 // Method to return the full name of the customer
 public string ReturnFullName()
 {
     return $"{FirstName} {LastName}";
 }

    The ReturnFullName method concatenates the FirstName and LastName properties to return the full name of the customer.

  4. To create a method that updates the customer’s name, add the following code:

    
 // Method to update the customer's name
 public void UpdateName(string firstName, string lastName)
 {
     FirstName = firstName;
     LastName = lastName;
 }

    The UpdateName method takes two parameters, firstName and lastName, and updates the FirstName and LastName properties with the new values.

  5. To create a method that displays customer information, add the following code:

    
 // Method to display customer information
 public string DisplayCustomerInfo()
 {
     return $"Customer ID: {CustomerId}, Name: {ReturnFullName()}";
 }

    The DisplayCustomerInfo method returns a string that includes the customer ID and the full name of the customer. It uses the ReturnFullName method to get the full name.

  6. Open the BankAccount.cs file.

    Account balances are affected by deposits, withdrawals, and transfers. The interest rate for an account can also affect the balance. You can create methods for each of these these behaviors. Once the deposit and withdrawal methods are implemented, the Balance property can be converted from an auto-implemented property to a property with a private backing field. This ensures that the account balance can only be updated through the methods.

  7. Create a blank code line below the final constructor.

  8. To create a method that deposits money into the account, add the following code:

    
 // Method to deposit money into the account
 public void Deposit(double amount)
 {
     if (amount > 0)
     {
         Balance += amount;
     }
 }

    The Deposit method takes an amount as a parameter and adds it to the Balance property if the amount is greater than zero.

  9. To create a method that withdraws money from the account, add the following code:

    
 // Method to withdraw money from the account
 public bool Withdraw(double amount)
 {
     if (amount > 0 && Balance >= amount)
     {
         Balance -= amount;
         return true;
     }
     return false;
 }

    The Withdraw method takes an amount as a parameter and subtracts it from the Balance property if the amount is greater than zero and the balance is sufficient. The method returns true if the withdrawal is successful and false otherwise.

  10. To create a method that transfers money to another account, add the following code:

    
 // Method to transfer money to another account
 public bool Transfer(BankAccount targetAccount, double amount)
 {
     if (Withdraw(amount))
     {
         targetAccount.Deposit(amount);
         return true;
     }
     return false;
 }

    The Transfer method takes a BankAccount object and an amount variable as parameters. It uses the Withdraw method to withdraw the amount value from the current account. It uses the target account’s Deposit method (targetAccount.Deposit) to deposit the amount value into the target account. The method returns true if the transfer is successful and false otherwise.

  11. To create a method that applies interest to the account balance, add the following code:

    
 // Method to apply interest to the account
 public void ApplyInterest()
 {
     Balance += Balance * InterestRate;
 }

    The ApplyInterest method calculates the interest on the account balance using the InterestRate field and adds the interest to the Balance property. At this point, the InterestRate field is a static field that’s shared among all instances of the BankAccount class. Since interest rate is initialized to 0, the ApplyInterest method doesn’t actually apply any interest. You can update the InterestRate field to a non-zero value in the static constructor to see the effect of the ApplyInterest method.

  12. Take a minute to consider the current implementation of the Balance property.

    
 public double Balance { get; set; } = 0;

    The Balance property currently uses auto-implemented property syntax. The { get; set; } syntax automatically creates a private backing field for the value, which is initialized to 0. Since Balance is declared public, the Balance property can be modified directly from outside the class, without going through the Deposit, Withdraw, or Transfer methods. This can lead to inconsistent account balances and make it difficult to track changes to the account balance.

    You can convert the Balance property to a read-only property with a private backing field to prevent direct modification of the balance value from outside the class. This ensures that the balance can only be updated through the Deposit, Withdraw, and Transfer methods.

  13. To convert the Balance property to a read-only property with a private backing field, replace the Balance property definition with the following code:

    
 public double Balance { get; private set; } = 0;

    The { get; private set; } syntax indicates that the Balance property has a private setter, meaning the value of the property can only be set from within the BankAccount class. The Balance property can still be read from outside the class, but it can only be updated through the Deposit, Withdraw, and Transfer methods.

  14. To create a method that displays account information, add the following code:

    
 // Method to display account information
 public string DisplayAccountInfo()
 {
     return $"Account Number: {AccountNumber}, Type: {AccountType}, Balance: {Balance}, Interest Rate: {InterestRate}, Customer ID: {CustomerId}";
 }

    The DisplayAccountInfo method returns a string that includes the account number, account type, balance, interest rate, and customer ID.

  15. Take a minute to review your updated BankCustomer and BankAccount classes.

    BankCustomer.cs

    
 public class BankCustomer
 {
     private static int s_nextCustomerId;
     private string _firstName = "Tim";
     private string _lastName = "Shao";
     public readonly string CustomerId;
        
     public string FirstName
     {
         get { return _firstName; }
         set { _firstName = value; }
     }
    
     public string LastName
     {
         get { return _lastName; }
         set { _lastName = value; }
     }
    
     static BankCustomer()
     {
         Random random = new Random();
         s_nextCustomerId = random.Next(10000000, 20000000);
     }
    
     public BankCustomer(string firstName, string lastName)
     {
         FirstName = firstName;
         LastName = lastName;
         this.CustomerId = (s_nextCustomerId++).ToString("D10");
     }
    
     // Method to return the full name of the customer
     public string ReturnFullName()
     {
         return $"{FirstName} {LastName}";
     }
    
     // Method to update the customer's name
     public void UpdateName(string firstName, string lastName)
     {
         FirstName = firstName;
         LastName = lastName;
     }
    
     // Method to display customer information
     public string DisplayCustomerInfo()
     {
         return $"Customer ID: {CustomerId}, Name: {ReturnFullName()}";
     }

 }

    BankAccount.cs

    
 public class BankAccount
 {
     private static int s_nextAccountNumber;
     public static double InterestRate;

     public int AccountNumber { get; }
     public string CustomerId { get; }
     public double Balance { get; private set; } = 0;
     public string AccountType { get; set; } = "Checking";
    
     static BankAccount()
     {
         Random random = new Random();
         s_nextAccountNumber = random.Next(10000000, 20000000);
         InterestRate = 0;
     }
    
     public BankAccount(string customerIdNumber)
     {
         this.AccountNumber = s_nextAccountNumber++;
         this.CustomerId = customerIdNumber;
     }
    
     public BankAccount(string customerIdNumber, double balance, string accountType)
     {
         this.AccountNumber = s_nextAccountNumber++;
         this.CustomerId = customerIdNumber;
         this.Balance = balance;
         this.AccountType = accountType;
     }
    
     // Method to deposit money into the account
     public void Deposit(double amount)
     {
         if (amount > 0)
         {
             Balance += amount;
         }
     }
    
     // Method to withdraw money from the account
     public bool Withdraw(double amount)
     {
         if (amount > 0 && Balance >= amount)
         {
             Balance -= amount;
             return true;
         }
         return false;
     }
    
     // Method to transfer money to another account
     public bool Transfer(BankAccount targetAccount, double amount)
     {
         if (Withdraw(amount))
         {
             targetAccount.Deposit(amount);
             return true;
         }
         return false;
     }

     // Method to apply interest to the account
     public void ApplyInterest()
     {
         Balance += Balance * InterestRate;
     }
    
     // Method to display account information
     public string DisplayAccountInfo()
     {
         return $"Account Number: {AccountNumber}, Type: {AccountType}, Balance: {Balance}, Interest Rate: {InterestRate}, Customer ID: {CustomerId}";
     }

 }

Create extension methods for the BankCustomer and BankAccount classes

Extension methods are a powerful feature in C# that allow you to add new methods to existing classes without modifying the original class. Extension methods are defined as static methods in a static class and are used as if they were instance methods of the extended class. If you have a class that you can’t modify (for example, a class from a third-party library), you can use extension methods to add new functionality to that class. If you have access to the source code of the class, adding the new methods directly to the class is recommended. However, extension methods are useful when you can’t or don’t want to modify the original class.

In this task, you create extension methods for the BankCustomer and BankAccount classes.

Use the following steps to complete this section of the exercise:

  1. Use the Classes_M2 project to create a new Extensions.cs class file.

    You can use the Classes_M2 project to create new class file named Extensions. Right-click the Classes_M2 project in the Solution Explorer, select New File, select Class, and then enter Extensions.

    Your Extensions class should look similar to the following code snippet:

    
 using System;

 namespace Classes_M2;

 public class Extensions
 {

 }

  2. To create a class that contains the extension methods for the BankCustomer class, replace the contents of the Extensions.cs file with the following code:

    
 using System;
    
 namespace Classes_M2;
    
 public static class BankCustomerExtensions
 {
     // Extension method to check if the customer ID is valid
     public static bool IsValidCustomerId(this BankCustomer customer)
     {
         return customer.CustomerId.Length == 10;
     }

     // Extension method to greet the customer
     public static string GreetCustomer(this BankCustomer customer)
     {
         return $"Hello, {customer.ReturnFullName()}!";
     }
 }

    The BankCustomerExtensions class contains two extension methods for the BankCustomer class:

    • IsValidCustomerId: This method checks if the customer ID is valid by verifying that the length of the customer ID is 10.
    • GreetCustomer: This method greets the customer by returning a string that says “Hello” followed by the customer’s full name. The extension method uses the ReturnFullName method of the BankCustomer class to get the full name.

  3. To create a class that contains the extension methods for the BankAccount class, add the following class definition to the end of the Extensions file:

    
 public static class BankAccountExtensions
 {
     // Extension method to check if the account is overdrawn
     public static bool IsOverdrawn(this BankAccount account)
     {
         return account.Balance < 0;
     }

     // Extension method to check if a specified amount can be withdrawn
     public static bool CanWithdraw(this BankAccount account, double amount)
     {
         return account.Balance >= amount;
     }
 }

    The BankAccountExtensions class contains two extension methods for the BankAccount class:

    • IsOverdrawn: This method checks if the account is overdrawn by verifying that the balance is less than zero.
    • CanWithdraw: This method checks if a specified amount can be withdrawn from the account by verifying that the balance is greater than or equal to the specified amount.

  4. Take a minute to review the Extensions.cs file:

    
 using System;
    
 namespace Classes_M2;

 public static class BankCustomerExtensions
 {
     // Extension method to check if the customer ID is valid
     public static bool IsValidCustomerId(this BankCustomer customer)
     {
         return customer.CustomerId.Length == 10;
     }

     // Extension method to greet the customer
     public static string GreetCustomer(this BankCustomer customer)
     {
         return $"Hello, {customer.ReturnFullName}!";
     }
 }

 public static class BankAccountExtensions
 {
     // Extension method to check if the account is overdrawn
     public static bool IsOverdrawn(this BankAccount account)
     {
         return account.Balance < 0;
     }

     // Extension method to check if a specified amount can be withdrawn
     public static bool CanWithdraw(this BankAccount account, double amount)
     {
         return account.Balance >= amount;
     }
 }

    [!NOTE] Extension methods are passed an instance of the class they’re extending as the first parameter. The this keyword before the parameter type indicates that the method is an extension method for that type. In this case, the this keyword appears before the BankCustomer and BankAccount types to indicate that the methods are extension methods for those classes.

Update the Program.cs file to demonstrate the updated classes, properties, and methods

In this task, you update the Program.cs file with code that demonstrates the following steps:

  1. Create BankCustomer objects.
  2. Create BankAccount objects for the instantiated customers.
  3. Demonstrate the use of BankCustomer properties. For example, update the customer’s name.
  4. Demonstrate the use of BankAccount methods. For example, deposit, withdraw, transfer, apply interest.
  5. Demonstrate the use of extension methods. For example, greet the customer, check if the customer ID is valid, check if the account is overdrawn, check if a specified amount can be withdrawn.
  6. Display customer and account information using the DisplayCustomerInfo and DisplayAccountInfo methods. These methods are defined in the BankCustomer and BankAccount classes, respectively.

Use the following steps to complete this section of the exercise:

  1. Open the Program.cs file.

  2. Replace the existing code with the following code:

    
 using Classes_M2;
    
 // Step 1: Create BankCustomer objects
 Console.WriteLine("Creating BankCustomer objects...");
 string firstName = "Tim";
 string lastName = "Shao";
    
 BankCustomer customer1 = new BankCustomer(firstName, lastName);
    
 firstName = "Lisa";
 BankCustomer customer2 = new BankCustomer(firstName, lastName);
    
 firstName = "Sandy";
 lastName = "Zoeng";
 BankCustomer customer3 = new BankCustomer(firstName, lastName);
    
 Console.WriteLine($"BankCustomer 1: {customer1.FirstName} {customer1.LastName} {customer1.CustomerId}");
 Console.WriteLine($"BankCustomer 2: {customer2.FirstName} {customer2.LastName} {customer2.CustomerId}");
 Console.WriteLine($"BankCustomer 3: {customer3.FirstName} {customer3.LastName} {customer3.CustomerId}");
    
 // Step 2: Create BankAccount objects for customers
 Console.WriteLine("\nCreating BankAccount objects for customers...");
 BankAccount account1 = new BankAccount(customer1.CustomerId);
 BankAccount account2 = new BankAccount(customer2.CustomerId, 1500, "Checking");
 BankAccount account3 = new BankAccount(customer3.CustomerId, 2500, "Checking");
    
 Console.WriteLine($"Account 1: Account # {account1.AccountNumber}, type {account1.AccountType}, balance {account1.Balance}, rate {BankAccount.InterestRate}, customer ID {account1.CustomerId}");
 Console.WriteLine($"Account 2: Account # {account2.AccountNumber}, type {account2.AccountType}, balance {account2.Balance}, rate {BankAccount.InterestRate}, customer ID {account2.CustomerId}");
 Console.WriteLine($"Account 3: Account # {account3.AccountNumber}, type {account3.AccountType}, balance {account3.Balance}, rate {BankAccount.InterestRate}, customer ID {account3.CustomerId}");
    
 // Step 3: Demonstrate the use of BankCustomer properties
 Console.WriteLine("\nUpdating BankCustomer 1's name...");
 customer1.FirstName = "Thomas";
 customer1.LastName = "Margand";
 Console.WriteLine($"Updated BankCustomer 1: {customer1.FirstName} {customer1.LastName} {customer1.CustomerId}");
    
 // Step 4: Demonstrate the use of BankAccount methods
 Console.WriteLine("\nDemonstrating BankAccount methods...");
    
 // Deposit
 Console.WriteLine("Depositing 500 into Account 1...");
 account1.Deposit(500);
 Console.WriteLine($"Account 1 after deposit: Balance = {account1.Balance}");
    
 // Withdraw
 Console.WriteLine("Withdrawing 200 from Account 2...");
 bool withdrawSuccess = account2.Withdraw(200);
 Console.WriteLine($"Account 2 after withdrawal: Balance = {account2.Balance}, Withdrawal successful: {withdrawSuccess}");
    
 // Transfer
 Console.WriteLine("Transferring 300 from Account 3 to Account 1...");
 bool transferSuccess = account3.Transfer(account1, 300);
 Console.WriteLine($"Account 3 after transfer: Balance = {account3.Balance}, Transfer successful: {transferSuccess}");
 Console.WriteLine($"Account 1 after receiving transfer: Balance = {account1.Balance}");
    
 // Apply interest
 Console.WriteLine("Applying interest to Account 1...");
 account1.ApplyInterest();
 Console.WriteLine($"Account 1 after applying interest: Balance = {account1.Balance}");
    
 // Step 5: Demonstrate the use of extension methods
 Console.WriteLine("\nDemonstrating extension methods...");
 Console.WriteLine(customer1.GreetCustomer());
 Console.WriteLine($"Is customer1 ID valid? {customer1.IsValidCustomerId()}");
 Console.WriteLine($"Can account2 withdraw 2000? {account2.CanWithdraw(2000)}");
 Console.WriteLine($"Is account3 overdrawn? {account3.IsOverdrawn()}");
    
 // Step 6: Display customer and account information
 Console.WriteLine("\nDisplaying customer and account information...");
 Console.WriteLine(customer1.DisplayCustomerInfo());
 Console.WriteLine(account1.DisplayAccountInfo());

  3. Notice that steps 4-6 demonstrate the use of the BankCustomer and BankAccount methods and extension methods.

    • Step 4 demonstrates the use of BankAccount methods to deposit, withdraw, transfer, and apply interest to the account balance.
    • Step 5 demonstrates the use of extension methods to greet the customer, check if the customer ID is valid, check if the account is overdrawn, and check if a specified amount can be withdrawn.
    • Step 6 displays customer and account information using the DisplayCustomerInfo and DisplayAccountInfo methods.

  4. Run the app and review the output in the terminal window.

    Your app should produce output that’s similar to the following example:

    
 Creating BankCustomer objects...
 BankCustomer 1: Tim Shao 0012396421
 BankCustomer 2: Lisa Shao 0012396422
 BankCustomer 3: Sandy Zoeng 0012396423
    
 Creating BankAccount objects for customers...
 Account 1: Account # 11657161, type Checking, balance 0, rate 0, customer ID 0012396421
 Account 2: Account # 11657162, type Checking, balance 1500, rate 0, customer ID 0012396422
 Account 3: Account # 11657163, type Checking, balance 2500, rate 0, customer ID 0012396423
    
 Updating BankCustomer 1's name...
 Updated BankCustomer 1: Thomas Margand 0012396421
    
 Demonstrating BankAccount methods...
 Depositing 500 into Account 1...
 Account 1 after deposit: Balance = 500
 Withdrawing 200 from Account 2...
 Account 2 after withdrawal: Balance = 1300, Withdrawal successful: True
 Transferring 300 from Account 3 to Account 1...
 Account 3 after transfer: Balance = 2200, Transfer successful: True
 Account 1 after receiving transfer: Balance = 800
 Applying interest to Account 1...
 Account 1 after applying interest: Balance = 800
    
 Demonstrating extension methods...
 Hello, Thomas Margand!
 Is customer1 ID valid? True
 Can account2 withdraw 2000? False
 Is account3 overdrawn? False
    
 Displaying customer and account information...
 Customer ID: 0012396421, Name: Thomas Margand
 Account Number: 11657161, Type: Checking, Balance: 800, Interest Rate: 0, Customer ID: 0012396421

Clean up

Now that you’ve finished the exercise, consider archiving your project files for review at a later time. Having your own projects available for review can be a valuable resource when you’re learning to code. Also, building up a portfolio of projects can be a great way to demonstrate your skills to potential employers.