Create class definitions and instantiate objects

In object-oriented programming, a class serves as a template for creating objects, which are the fundamental components of a program. In C#, classes are defined using the class keyword. Objects, the instances of a class, are instantiated using the new operator. Each object created from a class represents a specific realization of that class. Objects have their own data fields, and the values assigned to the fields can be different for each object.

In this exercise, you create a console app that uses class definitions to instantiate objects.

This exercise takes approximately 25 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 have experience creating structured apps in C#, but no experience with object-oriented programming. You need to gain experience before starting work on the company software. You decide to create a simple banking app that includes “BankCustomer” and “BankAccount” classes.

This exercise includes the following tasks:

  1. Create a console app and a class named BankCustomer.
  2. Update the Program.cs file to create instances of the BankCustomer class.
  3. Add public fields and updated constructors to the BankCustomer class.
  4. Update the BankCustomer class using static members to ensure unique customer IDs.
  5. Create a class named BankAccount that implements private, public, and static members.

Create a console app and a class named BankCustomer

In this task, you create a new console app, add a BankCustomer class to the project, and then create a class definition for the BankCustomer class. The class definition includes public fields and a parameterless constructor.

Use the following steps to complete this task:

  1. Open Visual Studio Code.

  2. Use Visual Studio Code to open a new folder named My CSharp Projects that’s located in the Windows Desktop folder.

    For example:

    1. On the Visual Studio Code welcome screen, select Open Folder. If the Welcome page isn’t displayed in the editor, open the File menu and select Open Folder.
    2. In the Open Folder dialog box, navigate to the Windows Desktop folder.
    3. Select New Folder and name the folder My CSharp Projects.
    4. Select the My CSharp Projects folder and then select Select Folder.

  3. Use the Command Palette to create a new console app named Classes_M1.

    For example:

    1. To open the Command Palette, press Ctrl+Shift+P.
    2. In the Command Palette, type .NET: and then select .NET: New Project.
    3. In the ‘Create a new .NET Project’ box, select Console App.
    4. In the ‘Name the new project’ box, type Classes_M1 and then press Enter.
    5. In the ‘Select location for the project’ box, select Default directory
    6. In the ‘Create project or view options’ box, select Create project

    You should see a new console app project named Classes_M1 in the Visual Studio Code EXPLORER view.

  4. If the Welcome page is still open in the Visual Studio Code editor, close the Welcome page.

  5. In the EXPLORER view, collapse the MY CSHARP PROJECTS folder structure, and then select SOLUTION EXPLORER.

    The Solution Explorer in Visual Studio Code is a feature provided by the C# Dev Kit extension. It offers a structured view of your application, its solutions, and its projects, making it easier to manage .NET projects within VS Code. When you open a workspace containing .NET solution files or project files, the Solution Explorer will automatically appear and load the solution files.

    Key features of the Solution Explorer include:

    • Automatically loading single or multiple solution files in a workspace.
    • Remembering the last loaded solution file for a workspace.
    • Providing context menu options for managing solutions and projects.
    • Supporting Solution Folders for organizing projects within a solution.

  6. Under SOLUTION EXPLORER, expand the Classes_M1 project and locate the Program.cs file.

    The structure of your solution should be similar to the following example:

     Classes_M1
     Classes_M1
         Dependencies
         Program.cs

  7. Hover the mouse pointer over the two Classes_M1 “folders” to reveal their association to the solution.

    The Classes_M1 folder at the top level of the solution represents the solution folder. The Classes_M1 folder nested under the solution folder represents the project folder. The Program.cs file is located within the project folder.

  8. Open the Program.cs file, and then delete the existing “hello, world” code.

  9. Right-click the Classes_M1 project, and then select New File.

    If you don’t see the option to create a new file, ensure that you’re accessing the Classes_M1 project folder not the Classes_M1 solution folder.

  10. In the ‘Create a new file’ dropdown, to create a class file named BankCustomer.cs, select Class and then enter BankCustomer.

    You should see a new file named BankCustomer.cs open in the Visual Studio Code editor. The file should be located in the Classes_M1 project folder, and the code should look similar to the following code snippet:

    
 using System;

 namespace Classes_M1;

 class BankCustomer
 {
    
 }

    At this point, your BankCustomer class definition is empty. You’ll add constructors and fields to the class during this task.

  11. Notice that a Classes_M1 namespace is specified.

    A namespace is a way to organize code in C#. It provides a way to group related classes and other types into a single unit. You can use this namespace to access the BankCustomer class from other classes in the project.

  12. To create a constructor for the BankCustomer class, add the following code to your BankCustomer class definition:

    
 public BankCustomer()
 {
     Console.WriteLine("BankCustomer created");
 }

    The BankCustomer class now includes a parameterless constructor that writes a message to the console when a new instance of the BankCustomer class is created.

  13. Your updated BankCustomer class should now look similar to the following code snippet:

    
 public class BankCustomer
 {
     public BankCustomer()
     {
         Console.WriteLine("BankCustomer created");
     }
 }

  14. To create a second constructor that accepts parameters for the bank customer’s first and last name, add the following code to your BankCustomer class definition:

    
 public BankCustomer(string firstName, string lastName)
 {
     Console.WriteLine($"BankCustomer created: {firstName} {lastName}");
 }

    The BankCustomer class now includes a second constructor that accepts parameters for the customer’s first and last name. The constructor writes a message to the console that includes the customer’s first and last name when a new instance of the BankCustomer class is created.

  15. Your updated BankCustomer class should now look similar to the following code snippet:

    
 public class BankCustomer
 {
     public BankCustomer()
     {
         Console.WriteLine("BankCustomer created");
     }

     public BankCustomer(string firstName, string lastName)
     {
         Console.WriteLine($"BankCustomer created: {firstName} {lastName}");
     }
 }

Update the Program.cs file to create instances of the BankCustomer class

The new operator is used to create objects based on a class constructor. Each object has its own data fields, and the values assigned to the fields can be different for each object.

In this task, you update the Program.cs file to create instances of the BankCustomer class and run the app to verify that the instances are created successfully.

Use the following steps to complete this task:

  1. Switch to the Program.cs file

    You’re using the Program.cs file to create instances of the BankCustomer class, but at this point it should be empty. If the “hello, world” code is still present, delete it now.

  2. To create a using statement that specifies the namespace defined by the customer BankCustomer class, add the following code to the Program.cs file:

    
 using Classes_M1;

    This using statement allows you to access the BankCustomer class from within the Program.cs file.

  3. To create an instance of the BankCustomer class, add the following code to the Program.cs file:

    
 BankCustomer customer1 = new BankCustomer();

    The new operator is used to create a new instance of the BankCustomer class. The BankCustomer class constructor is called when the new instance is created.

  4. To create a second instance of the BankCustomer class using the second constructor, add the following code to the Program.cs file:

    
 BankCustomer customer2 = new BankCustomer("Tim", "Shao");

    The BankCustomer class constructor that accepts parameters for the customer’s first and last name is called when the new instance is created. The constructor writes a message to the console that includes the customer’s first and last name.

  5. Take a minute to review your Program.cs and BankCustomer.cs files.

    Program.cs file:

    
 using Classes_M1;
    
 BankCustomer customer1 = new BankCustomer();

 BankCustomer customer2 = new BankCustomer("Tim", "Shao");

    BankCustomer.cs file:

    
 using System;

 namespace Classes_M1;

 public class BankCustomer
 {
     public BankCustomer()
     {
         Console.WriteLine("BankCustomer created");
     }

     public BankCustomer(string firstName, string lastName)
     {
         Console.WriteLine($"BankCustomer created: {firstName} {lastName}");
     }
 }

  6. Ensure that you’ve saved your changes to both files.

    Visual Studio Code can be configured to automatically save changes for you. If you haven’t configured Visual Studio Code to automatically save changes, you can manually save your changes by selecting File > Save or File > Save ALL from the top menu bar.

  7. To ensure that your solution builds without errors, right-click the Classes_M1 solution in the Solution Explorer, and then select Build.

    If you don’t see the Build option listed, ensure that you’ve selected the Classes_M1 solution in the Solution Explorer. The Build option isn’t available when a project is selected.

    You need to fix any errors before you can run your app.

  8. To run your app, right-click the Classes_M1 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_M1 project in the Solution Explorer. The Debug option isn’t available when a solution is selected.

    There are several ways to run your app in Visual Studio Code. For example:

    • You can use the Run menu
    • You can select the Run button in the top menu bar
    • You can use the F5 key
    • You can use the Terminal panel and type dotnet run

    Any of these options is fine. Some options are more convenient than others, depending on your preferences. Also, some options use the debugger, which can be helpful when you need to step through your code.

  9. Review the output in the Debug Console panel.

    You should see the following output:

    
 BankCustomer created
 BankCustomer created: Tim Shao

Add public fields and updated constructors to the BankCustomer class

Public fields are accessible from outside the class. They can be read from and written to by any code that has access to the object. Public fields are often used to expose object data to other classes.

In this task, you add public fields to the BankCustomer class, update the instance constructors to use additional parameters, and then update the Program.cs file to access each object’s public data.

Use the following steps to complete this task:

  1. Open the BankCustomer.cs file.

  2. Add the following public fields to the class definition:

    
 public string FirstName = "Tim";
 public string LastName = "Shao";
 public string CustomerId = "1010101010";

    Notice that the fields are initialized with default values.

  3. Update the second constructor to assign constructor parameters to the local variables.

    
 public BankCustomer(string firstName, string lastName)
 {
     FirstName = firstName;
     LastName = lastName;

     Console.WriteLine($"BankCustomer created: {firstName} {lastName}");
 }

  4. Delete the Console.WriteLine() messages from the constructors.

    You’ll update the Program.cs file to display object data using the public fields. The updated constructors should be similar to the following code snippet:

    
 public BankCustomer()
 {

 }

 public BankCustomer(string firstName, string lastName)
 {
     FirstName = firstName;
     LastName = lastName;

 }

  5. To create a third constructor that accepts firstName, lastName, and customerIdNumber parameters, add the following code to the BankCustomer class definition:

    
 public BankCustomer(string firstName, string lastName, string customerIdNumber)
 {
     FirstName = firstName;
     LastName = lastName;
     CustomerId = customerIdNumber;
 }

    The constructor initializes the FirstName, LastName, and CustomerId fields with the values of the firstName, lastName, and customerIdNumber parameters, respectively.

  6. Switch to the Program.cs file

  7. To create local variables for firstName, lastName, and customerIdNumber just below the namespace declaration, enter the following code:

    
 string firstName = "Tim";
 string lastName = "Shao";
 string customerIdNumber = "1010101010";

  8. To use firstName and lastName when creating customer2, replace your existing code for customer2 with the following code snippet:

    
 firstName = "Lisa";
 BankCustomer customer2 = new BankCustomer(firstName, lastName);

  9. To create a third object named customer3 that uses your third constructor, add the following code to the Program.cs file:

    
 firstName = "Sandy";
 lastName = "Zoeng";
 customerIdNumber = "2020202020";
 BankCustomer customer3 = new BankCustomer(firstName, lastName, customerIdNumber);

  10. To display the public data fields for each object, add the following code to the end of the Program.cs file:

    
 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}");

  11. Take a minute to review your updated code files.

    Program.cs file:

    
 using Classes_M1;

 namespace Classes_M1;

 string firstName = "Tim";
 string lastName = "Shao";
 string customerIdNumber = "1010101010";
    
 BankCustomer customer1 = new BankCustomer();
    
 firstName = "Lisa";
 BankCustomer customer2 = new BankCustomer(firstName, lastName);
    
 firstName = "Sandy";
 lastName = "Zoeng";
 customerIdNumber = "2020202020";
 BankCustomer customer3 = new BankCustomer(firstName, lastName, customerIdNumber);
    
 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}");

    BankCustomer.cs file:

    
 using System;

 namespace Classes_M1;

 public class BankCustomer
 {
     // add public fields for FirstName, LastName, and CustomerId
     public string FirstName = "Tim";
     public string LastName = "Shao";
     public string CustomerId = "1010101010";
    
     public BankCustomer()
     {
    
     }
    
     public BankCustomer(string firstName, string lastName)
     {
         FirstName = firstName;
         LastName = lastName;
    
     }
    
     public BankCustomer(string firstName, string lastName, string customerIdNumber)
     {
         FirstName = firstName;
         LastName = lastName;
         CustomerId = customerIdNumber;
     }
 }

  12. Run your updated app and verify that you get the following output:

    You should see the following output:

    
 BankCustomer 1: Tim Shao 1010101010
 BankCustomer 2: Lisa Doe 1010101010
 BankCustomer 3: Sandy Zoeng 2020202020

  13. Notice that the first two customers share the same ID number.

    The BankCustomer class initializes data fields using default values. Although the constructors update field values using parameters, the current approach doesn’t ensure unique customer IDs.

Update the BankCustomer class using static members to ensure unique customer IDs

Static fields are initialized before an instance of the class is created. When an object is created, static fields are accessed using the class name, not an instance of the class. The same value is shared by all instances of the class.

Static constructors are called when a class is loaded into memory. A static constructor is called only once, regardless of how many instances of the class are created. Static constructors are used to initialize static fields.

In this task, you update the BankCustomer class using a static field and static constructor to ensure unique CustomerId values are assigned to each new customer object.

Use the following steps to complete this task:

  1. Open the BankCustomerclass.

  2. To convert CustomerId into a read-only field, add the readonly keyword to the CustomerId field declaration:

    
 public readonly string CustomerId;

    Notice that CustomerId is no longer initialized when it’s declared. The readonly keyword is used to declare a field that can be assigned a value only when it’s declared or in a constructor. In this case, you’ll assign a unique value to CustomerId in the constructors, so no value is assigned when the field is declared.

  3. To create a static field named s_nextCustomerId, add the following code to the BankCustomer class definition:

    
 private static int s_nextCustomerId;

    The s_nextCustomerId field is used to ensure that each new instance of the BankCustomer class is assigned a unique customer ID. The field is declared as a static field, which means that it’s shared among all instances of the BankCustomer class.

  4. To create a static constructor that initializes the s_nextCustomerId field, add the following code to the BankCustomer class definition:

    
 static BankCustomer()
 {
     Random random = new Random();
     s_nextCustomerId = random.Next(10000000, 20000000);
 }

    The static constructor is called when the BankCustomer class is loaded into memory, and before any instances of the class are created. The static constructor initializes the s_nextCustomerId field with a random eight digit integer.

  5. To assign a unique value to CustomerId inside your parameterless constructor, update the constructor to match the following code:

    
 public BankCustomer()
 {
     this.CustomerId = (s_nextCustomerId++).ToString("D10");
 }

    The updated constructor initializes the CustomerId field using the already initialized s_nextCustomerId field. Notice that s_nextCustomerId is incremented by 1 before the CustomerId field is assigned a value.

    [!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.

  6. To assign a unique value to CustomerId inside your constructor that accepts firstName and lastName parameters, update the constructor to match the following code:

    
 public BankCustomer(string firstName, string lastName)
 {
     FirstName = firstName;
     LastName = lastName;
     this.CustomerId = (s_nextCustomerId++).ToString("D10");
 }

    Once again, the constructor initializes the CustomerId field using an incremented s_nextCustomerId value.

  7. Delete the constructor that accepts the firstName, lastName, and customerIdNumber parameters.

    Ensuring unique customer IDs includes removing the opportunity to create a new customer with an externally provided ID. Also, your parameterless and static constructors ensure that every new instance of the BankCustomer class is assigned a unique customer ID.

  8. Switch to the Program.cs file.

  9. Locate the code line that’s used to create customer3:

    
 BankCustomer customer3 = new BankCustomer(firstName, lastName, customerIdNumber);

  10. Replace the code line with the following code:

    
 BankCustomer customer3 = new BankCustomer(firstName, lastName);

  11. Since the CustomerId field is no longer accepted as a constructor parameter, you can delete the following references to the customerIdNumber variable in Program.cs.

    
 string customerIdNumber = "1010101010"; // delete this line near the top of the file
 customerIdNumber = "2020202020"; // delete this line just before creating customer3

  12. Take a minute to review the updated Program.cs and BankCustomer.cs files.

    Program.cs file:

    
 using Classes_M1;

 string firstName = "Tim";
 string lastName = "Shao";
    
 BankCustomer customer1 = new BankCustomer();
    
 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}");

    BankCustomer.cs file:

    
 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()
     {
         this.CustomerId = (s_nextCustomerId++).ToString("D10");
     }
    
     public BankCustomer(string firstName, string lastName)
     {
         FirstName = firstName;
         LastName = lastName;
         this.CustomerId = (s_nextCustomerId++).ToString("D10");
     }
 }

Create a class named BankAccount that implements private, public, and static members

In this task, you create an BankAccount class that initializes a combination of public and static fields. You also create constructors that initialize the fields with default values and values passed as parameters.

You want a BankAccount class that includes the following fields:

  • AccountNumber - A public field that stores the account number.
  • Balance - A public field that stores the account balance.
  • InterestRate - A static field that stores the interest rate.
  • AccountType - A public field that stores the account type.
  • CustomerId - A public field that stores the customer ID associated with the account. This field must be read-only.
  • s_nextAccountNumber - A static field that stores the next account number. This field is used to ensure that each object is assigned a unique account number.

Use the following steps to complete this task:

  1. Use the Classes_M1 project to create a class named BankAccount.

    You can use the Classes_M1 project to create the BankAccount class. Right-click the Classes_M1 project in the Solution Explorer, select New File, select Class, and then enter BankAccount.

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

    
 using System;

 namespace Classes_M1;

 public class BankAccount
 {

 }

  2. To create public fields for the AccountNumber, Balance, InterestRate, AccountType, and CustomerId fields, add the following code to the BankAccount class definition:

    
 public int AccountNumber;
 public double Balance = 0;
 public static double InterestRate;
 public string AccountType = "Checking";
 public readonly string CustomerId;

    Notice that the InterestRate field is declared as static and that CustomerId is declared as readonly. Static fields are accessed using the class name, not an instance of the class, and are shared among all instances of a class. The value of a static field is initialized before an instance of the class is created. Readonly fields can be assigned a value only when they’re declared or in a constructor.

  3. To create a static field named s_nextAccountNumber, add the following code to the BankAccount class definition:

    
 private static int s_nextAccountNumber = 1;

    The s_nextAccountNumber field is used to ensure that each new instance of the BankAccount class is assigned a unique account number. The field is initialized with a value of 1.

  4. To create a static constructor that initializes the s_nextAccountNumber and InterestRate fields, add the following code to the BankAccount class definition:

    
 static BankAccount()
 {
     Random random = new Random();
     s_nextAccountNumber = random.Next(10000000, 20000000);
     InterestRate = 0;
 }

    The static constructor is called when the BankAccount class is loaded into memory. The static constructor initializes the s_nextAccountNumber and InterestRate fields. These fields cannot be assigned a value from outside the class.

  5. To create a constructor that accepts a CustomerId parameter and initializes the other fields with default values, add the following code to the BankAccount class definition:

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

    The constructor initializes the AccountNumber field using the s_nextAccountNumber field. The CustomerId field is initialized with the value of the customerIdNumber parameter.

  6. To create a constructor that accepts parameters for the CustomerId, Balance, and AccountType fields, add the following code to the BankAccount class definition:

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

    The constructor initializes the AccountNumber field using the s_nextAccountNumber field. The CustomerId, Balance, and AccountType fields are initialized with the values of the customerIdNumber, Balance, and AccountType parameters, respectively.

  7. Switch to the Program.cs file.

  8. To create instances of the BankAccount class, add the following code to the end of the Program.cs file:

    
 BankAccount account1 = new BankAccount(customer1.CustomerId);
 BankAccount account2 = new BankAccount(customer2.CustomerId, 1500, "Checking");
 BankAccount account3 = new BankAccount(customer3.CustomerId, 2500, "Checking");

    The new operator is used to create new instances of the BankAccount class. The constructors are called when the new instances are created.

  9. To display the public data fields for each of the bank account objects, add the following code to the end of the Program.cs file:

    
 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. Take a minute to review your code files.

    Program.cs file:

    
 using Classes_M1;
    
 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}");

    BankCustomer.cs file:

    
 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");
     }
        
 }

    BankAccount.cs file:

    
 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;
     }
 }

  11. 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.

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.