A Database as an Array of Values

1. Start Microsoft Visual Basic and create a Windows Forms Application named YugoNationalBank1
2. In the Solution Explorer, right-click Form1.vb and click Rename
3. Type Central.vb and press Enter

Before creating an array, you must decide what type of values each element of the array would be. A simple array can be made of primitive types of values. Here is an example:

Private Sub Exercise_Load(ByVal sender As Object, _
                          ByVal e As System.EventArgs) Handles Me.Load
    Dim Numbers() As Double = { 12.44, 525.38, 6.28, 2448.32, 632.04 }
End Sub

Once the array has been created, you can access each one of its elements using the () operator. Here is an example:

Private Sub Exercise_Load(ByVal sender As Object, _
                          ByVal e As System.EventArgs) Handles Me.Load
    Dim Numbers() As Double = { 12.44, 525.38, 6.28, 2448.32, 632.04 }

    For i As Integer = 0 To 4
        lbxNumbers.Items.Add(Numbers(i))
    Next
End Sub

An array can also be made of elements that are each a composite type. That is, each element can be of a class type. Of course, you must have a class first. You can use one of the many built-in classes of the .NET Framework or you can create your own class. Here is an example:

Public Class Person
    Public PersonID As Integer
    Public FirstName As String
    Public LastName As String
    Public Gender As String

    Public Sub New()

    End Sub

    Public Sub New(ByVal ID As Integer, ByVal FName As String, _
                   ByVal LName As String, ByVal Gdr As String)
        PersonID = ID
        FirstName = FName
        LastName = LName
        Gender = Gdr
    End Sub

End Class

After creating the class, you can then use it as the type of the array. Here is an example:

Private Sub Exercise_Load(ByVal sender As Object, _
                          ByVal e As System.EventArgs) Handles Me.Load
        Dim People(7) As Person

        People(0) = New Person(72947, "Paulette", _
                               "Cranston", "Female")
        People(1) = New Person(70854, "Harry", _
                               "Kumar", "Male")
        People(2) = New Person(27947, "Jules", _
                               "Davidson", "Male")
        People(3) = New Person(62835, "Leslie", _
                               "Harrington", "Unknown")
        People(4) = New Person(92958, "Ernest", _
                               "Colson", "Male")
        People(5) = New Person(91749, "Patricia", _
                               "Katts", "Female")
        People(6) = New Person(29749, "Patrice", _
                               "Abanda", "Unknown")
        People(7) = New Person(24739, "Frank", _
                               "Thomasson", "Male")

        For i As Integer = 0 To 7
            Dim lviPerson As ListViewItem = New ListViewItem(People(i).FirstName)

            lviPerson.SubItems.Add(People(i).LastName)
            lviPerson.SubItems.Add(People(i).Gender)

            lvwPeople.Items.Add(lviPerson)
        Next
End Sub

To assist you with creating or managing arrays, the .NET Framework provides the Array class. Every array you create is derived from this class. As a result, all arrays of your program share many characteristics and they get their foundation from the Array class, which include its properties and methods. Once you declare an array variable, it automatically has access to the members of the Array class. For example, instead of counting the number of elements in an array, you can access the Length property of the array variable. Here is an example:

Private Sub Exercise_Load(ByVal sender As Object, _
                              ByVal e As System.EventArgs) Handles Me.Load
        Dim Numbers() As Integer = {20, 5, 83405, 734, 5}

        For i As Integer = 0 To Numbers.Length - 1
            lbxNumbers.Items.Add(Numbers(i))
        Next
End Sub

In traditional languages, when you declare an array variable, you must specify the number of elements that the array will contain. You must do this especially if you declare the variable without initializing the array. Here is an example:

Private Sub Exercise_Load(ByVal sender As Object, _
                              ByVal e As System.EventArgs) Handles Me.Load
        dim People(4) as Person
End Sub

After declaring the variable, before using the array, you must initialize it. Otherwise you would receive an error. When initializing the array, you can only initialize it with the number of elements you had specified. To illustrate this, consider the following program:

Private Sub Exercise_Load(ByVal sender As Object, _
                              ByVal e As System.EventArgs) Handles Me.Load
        Dim People(4) As Person

        People(0) = New Person(72947, "Paulette", _
                               "Cranston", "Female")
        People(1) = New Person(70854, "Harry", _
                               "Kumar", "Male")
        People(2) = New Person(27947, "Jules", _
                               "Davidson", "Male")
        People(3) = New Person(62835, "Leslie", _
                               "Harrington", "Unknown")
        People(4) = New Person(92958, "Ernest", _
                               "Colson", "Male")

        For i As Integer = 0 To People.Length - 1
            Dim lviPerson As ListViewItem = New ListViewItem(People(i).FirstName)

            lviPerson.SubItems.Add(People(i).LastName)
            lviPerson.SubItems.Add(People(i).Gender)

            lvwPeople.Items.Add(lviPerson)
        Next
End Sub

Notice that the variable is declared to hold only 4 elements but the user tries to access a 5th one. This would produce an IndexOutOfRangeExcception exception:

One of the most valuable features of the Array class is that it allows an array to be "resizable". That is, if you find out that an array has a size smaller than the number of elements you want to add to it, you can increase its capacity. To support this, the Array class is equipped with the static Resize() method. Its syntax is:

Public Shared Sub Resize(Of T) (ByRef array As T(), newSize As Integer)

As you can see, this is a generic method that takes two arguments. The first argument is the name of the array variable that you want to resize. It must be passed by reference. The second argument is the new size you want the array to have. Here is an example of calling this method:

Public Class Exercise

    Private Sub Exercise_Load(ByVal sender As Object, _
                              ByVal e As System.EventArgs) Handles Me.Load
        Dim People(4) As Person

        People(0) = New Person(72947, "Paulette", _
                               "Cranston", "Female")
        People(1) = New Person(70854, "Harry", _
                               "Kumar", "Male")
        People(2) = New Person(27947, "Jules", _
                               "Davidson", "Male")
        People(3) = New Person(62835, "Leslie", _
                               "Harrington", "Unknown")
        People(4) = New Person(92958, "Ernest", _
                              "Colson", "Male")

        Array.Resize(Of Person)(People, 8)

        People(5) = New Person(91749, "Patricia", _
                              "Katts", "Female")
        People(6) = New Person(29749, "Patrice", _
                              "Abanda", "Unknown")
        People(7) = New Person(24739, "Frank", _
                              "Thomasson", "Male")

        For i As Integer = 0 To People.Length - 1
            Dim lviPerson As ListViewItem = New ListViewItem(People(i).FirstName)

            lviPerson.SubItems.Add(People(i).LastName)
            lviPerson.SubItems.Add(People(i).Gender)

            lvwPeople.Items.Add(lviPerson)
        Next
    End Sub
End Class

The advantage of this approach is that you can access the array from any member of the same class or even from another file of the same program.

As done previously, you can create an array in a method. A disadvantage of this approach is that the array can be accessed from only the method (or event) in which it is created. As an alternative, you can declare an array as a member of a class. Here is an example:

Public Class Exercise
    Dim People() As Person
End Class

The advantage of this approach is that you can access the array from any member of the same class or even from another file of the same program. After declaring the variable, you can initialize it. You can do this in a constructor or in an event that would be fired before any other event that would use the array. This type of initialization is usually done in a Load event of a form. After initializing the array, you can then access in another method or another event of the form. Here is an example:

Public Class Exercise
    Dim People(7) As Person

    Private Sub Exercise_Load(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) Handles MyBase.Load
        People(0) = New Person(72947, "Paulette", _
                               "Cranston", "Female")
        People(1) = New Person(70854, "Harry", _
                               "Kumar", "Male")
        People(2) = New Person(27947, "Jules", _
                               "Davidson", "Male")
        People(3) = New Person(62835, "Leslie", _
                               "Harrington", "Unknown")
        People(4) = New Person(92958, "Ernest", _
                              "Colson", "Male")
        People(5) = New Person(91749, "Patricia", _
                              "Katts", "Female")
        People(6) = New Person(29749, "Patrice", _
                              "Abanda", "Unknown")
        People(7) = New Person(24739, "Frank", _
                              "Thomasson", "Male")

        For i As Integer = 0 To People.Length - 1
            Dim lviPerson As ListViewItem = New ListViewItem(People(i).FirstName)

            lviPerson.SubItems.Add(People(i).LastName)
            lviPerson.SubItems.Add(People(i).Gender)

            lvwPeople.Items.Add(lviPerson)
        Next
    End Sub
End Class

An array can be passed as argument to a method. Here is an example:

Public Class Exercise
    Private Sub ArrayInitializer(ByVal People() As Person)

    End Sub
End Class

In the method, you can use the array as you see fit. For example you can assign values to the elements of the array. When calling a method that is passed an array, you can pass the argument by reference so it would come back with new values. Here are examples:

Public Class Exercise
    Private Sub ArrayInitializer(ByVal People() As Person)
        People(0) = New Person(72947, "Paulette", _
                               "Cranston", "Female")
        People(1) = New Person(70854, "Harry", _
                               "Kumar", "Male")
        People(2) = New Person(27947, "Jules", _
                               "Davidson", "Male")
        People(3) = New Person(62835, "Leslie", _
                               "Harrington", "Unknown")
        People(4) = New Person(92958, "Ernest", _
                              "Colson", "Male")
        People(5) = New Person(91749, "Patricia", _
                              "Katts", "Female")
        People(6) = New Person(29749, "Patrice", _
                              "Abanda", "Unknown")
        People(7) = New Person(24739, "Frank", _
                              "Thomasson", "Male")
    End Sub

    Private Sub ShowPeople(ByVal People() As Person)
        For i As Integer = 0 To People.Length - 1
            Dim lviPerson As ListViewItem = New ListViewItem(People(i).FirstName)

            lviPerson.SubItems.Add(People(i).LastName)
            lviPerson.SubItems.Add(People(i).Gender)

            lvwPeople.Items.Add(lviPerson)
        Next
    End Sub

    Private Sub Exercise_Load(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) Handles MyBase.Load
        Dim Persons(7) As Person

        ArrayInitializer(Persons)
        ShowPeople(Persons)
    End Sub
End Class

A method can be created to return an array. When creating the method, on the right side of the name of the method, type the name of the type of value the method would return. In the method, create and initialize an array. Before exiting the method, you must return the array. Here is an example:

Public Class Exercise
    Private Function ArrayInitializer() As Person()

        Dim People(7) As Person

        People(0) = New Person(72947, "Paulette", _
                               "Cranston", "Female")
        People(1) = New Person(70854, "Harry", _
                               "Kumar", "Male")
        People(2) = New Person(27947, "Jules", _
                               "Davidson", "Male")
        People(3) = New Person(62835, "Leslie", _
                               "Harrington", "Unknown")
        People(4) = New Person(92958, "Ernest", _
                              "Colson", "Male")
        People(5) = New Person(91749, "Patricia", _
                              "Katts", "Female")
        People(6) = New Person(29749, "Patrice", _
                              "Abanda", "Unknown")
        People(7) = New Person(24739, "Frank", _
                              "Thomasson", "Male")

        Return People
    End Function

    Private Sub ShowPeople(ByVal People() As Person)
        For i As Integer = 0 To People.Length - 1
            Dim lviPerson As ListViewItem = New ListViewItem(People(i).FirstName)

            lviPerson.SubItems.Add(People(i).LastName)
            lviPerson.SubItems.Add(People(i).Gender)

            lvwPeople.Items.Add(lviPerson)
        Next
    End Sub

    Private Sub Exercise_Load(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) Handles MyBase.Load
        Dim Persons(7) As Person

        Persons = ArrayInitializer()
        ShowPeople(Persons)
    End Sub
End Class

1. To create a new class, on the main menu, click Project -> Add Class...
2. Set the name to Employee and press Enter
3. Complete the file as follows:
    

   Public Class Employee Public EmployeeNumber As Integer Public FirstName As String Public LastName As String Public Title As String Public CanCreateNewAccount As Boolean Public HourlySalary As Double Public ReadOnly Property FullName() As String Get Return LastName & ", " & FirstName End Get End Property End Class

4. To create a form that will be used to displays the employees information, on the main menu, click Project -> Add Windows Form
5. Set the name to Employees and press Enter
6. Design the form as follows:
    

   Control Text Name Other Properties ListView   lvwEmployees FullRowSelect: True GridLines: True View: Details Columns (Name) Text TextAlign Width colIndex #   20 colEmployeeNumber Empl #   50 colFirstName First Name   65 colLastName Last Name   65 colFullName Full Name   95 colTitle Title   145 colHourlySalary Salary Right 50 Button Close btnClose

7. To create a new class, on the main menu, click Project -> Add Class...
8. Set the name to Customer and press Enter
9. Complete the file as follows:
    

   Public Enum AccountStatus Active Suspended Closed End Enum Public Class Customer Public CreatedBy As String Public DateCreated As DateTime Public CustomerName As String Public AccountNumber As String Public AccountType As String Public Status As AccountStatus End Class

10. To create a form that will show the customers information, on the main menu, click Project -> Add Windows Form
11. Set the name to Customers and press Enter
12. Design the form as follows:
     

    Control Text Name Other Properties ListView   lvwCustomers FullRowSelect: True GridLines: True View: Details Columns (Name) Text TextAlign Width colIndex #   20 colCreatedBy Created By   100 colDateCreated Date Created Center 75 colCustomerName Customer Name   120 colAccountNumber Account # Center 80 colAccountType Account Type   80 coloAccountStatus Status   50 Button Close btnClose

13. Double-click the Close button and implement its event as follows:
     

    Private Sub btnClose_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles btnClose.Click Close() End Sub

14. To create a new class, on the main menu, click Project -> Add Class...
15. Set the name to AccountTransaction and press Enter
16. Complete the file as follows:
     

    Public Enum TransactionTypes Deposit Withdrawal Transfer MonthlyCharge MoneyOrder Overdraft TransactionFee End Enum Public Class AccountTransaction Public TransactionDate As DateTime Public ProcessedBy As Integer Public ProcessedFor As String Public TransactionType As TransactionTypes Public DepositAmount As Double Public WithdrawalAmount As Double Public ChargeAmount As Double End Class

17. To create a new form that will show the transactions done on the customers accounts, on the main menu, click Project -> Add Windows Form
18. Set the name to CustomersTransactions and press Enter
19. Design the form as follows:
     

    Control Text Name Other Properties ListView   lvwTransactions FullRowSelect: True GridLines: True View: Details Columns (Name) Text TextAlign Width colIndex #   25 colTransactionDate Trans Date Center 80 colProcessedBy Processed By Center 80 colProcessedFor Processed For Center 90 colTransactionType Trans Type   90 colDepositAmount Deposit Right   colWithdrawalAmount Withdrawal Right 65 colChargeAmount Charge Right 50 Button Close btnClose

20. Double-click the Close button and implement its event as follows:
     

    Private Sub btnClose_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles btnClose.Click Close() End Sub

21. To create a new class, on the main menu, click Project -> Add Class...
22. Set the name to AccountsRecords and press Enter
23. Complete the file as follows:
     

    Public Class AccountsRecords Public Shared Function GetEmployees() As Employee() Dim StaffMembers(6) As Employee StaffMembers(0) = New Employee StaffMembers(0).EmployeeNumber = 74228 StaffMembers(0).FirstName = "Chrissie" StaffMembers(0).LastName = "Nomads" StaffMembers(0).Title = "General Manager" StaffMembers(0).CanCreateNewAccount = True StaffMembers(0).HourlySalary = 40.25 StaffMembers(1) = New Employee StaffMembers(1).EmployeeNumber = 27905 StaffMembers(1).FirstName = "Calvin" StaffMembers(1).LastName = "Braxton" StaffMembers(1).Title = "Public Relations Manager" StaffMembers(1).CanCreateNewAccount = False StaffMembers(1).HourlySalary = 25.95 StaffMembers(2) = New Employee() StaffMembers(2).EmployeeNumber = 94805 StaffMembers(2).FirstName = "Emilie" StaffMembers(2).LastName = "Pastore" StaffMembers(2).Title = "Branch Manager" StaffMembers(2).CanCreateNewAccount = True StaffMembers(2).HourlySalary = 32.55 StaffMembers(3) = New Employee() StaffMembers(3).EmployeeNumber = 39850 StaffMembers(3).FirstName = "Walter" StaffMembers(3).LastName = "Lemme" StaffMembers(3).Title = "Accounts Manager" StaffMembers(3).CanCreateNewAccount = True StaffMembers(3).HourlySalary = 28.35 StaffMembers(4) = New Employee() StaffMembers(4).EmployeeNumber = 70594 StaffMembers(4).FirstName = "Cecile" StaffMembers(4).LastName = "Richards" StaffMembers(4).Title = "Accounts Representative" StaffMembers(4).CanCreateNewAccount = False StaffMembers(4).HourlySalary = 18.15 StaffMembers(5) = New Employee() StaffMembers(5).EmployeeNumber = 85285 StaffMembers(5).FirstName = "Joan" StaffMembers(5).LastName = "Verrion" StaffMembers(5).Title = "Accounts Representative" StaffMembers(5).CanCreateNewAccount = False StaffMembers(5).HourlySalary = 14.85 StaffMembers(6) = New Employee() StaffMembers(6).EmployeeNumber = 94852 StaffMembers(6).FirstName = "Donald" StaffMembers(6).LastName = "Waters" StaffMembers(6).Title = "Accounts Representative" StaffMembers(6).CanCreateNewAccount = False StaffMembers(6).HourlySalary = 16.45 Return StaffMembers End Function Public Shared Function GetCustomers() As Customer() Dim Clients(4) As Customer Clients(0) = New Customer Clients(0).CreatedBy = "Lemme, Walter" Clients(0).DateCreated = New DateTime(2007, 1, 16) Clients(0).CustomerName = "Louis George Berholdt" Clients(0).AccountNumber = "95-722947-93" Clients(0).AccountType = "Checking" Clients(0).Status = AccountStatus.Active Clients(1) = New Customer() Clients(1).CreatedBy = "Pastore, Emilie" Clients(1).DateCreated = New DateTime(2007, 1, 18) Clients(1).CustomerName = "William Foster" Clients(1).AccountNumber = "62-384638-48" Clients(1).AccountType = " Checking" Clients(1).Status = AccountStatus.Active Clients(2) = New Customer() Clients(2).CreatedBy = "Lemme, Walter" Clients(2).DateCreated = New DateTime(2007, 1, 18) Clients(2).CustomerName = "Catherine Hoods" Clients(2).AccountNumber = "92-318284-75" Clients(2).AccountType = "Checking" Clients(2).Status = AccountStatus.Active Clients(3) = New Customer() Clients(3).CreatedBy = "Lemme, Walter" Clients(3).DateCreated = New DateTime(2007, 3, 26) Clients(3).CustomerName = "Harriett Cranston" Clients(3).AccountNumber = "17-490040-83" Clients(3).AccountType = "Saving" Clients(3).Status = AccountStatus.Active Clients(4) = New Customer() Clients(4).CreatedBy = "Nomads, Chrissie" Clients(4).DateCreated = New DateTime(2007, 4, 4) Clients(4).CustomerName = "Janice Bonnie Weiss" Clients(4).AccountNumber = "58-405048-15" Clients(4).AccountType = "Checking" Clients(4).Status = AccountStatus.Active Return Clients End Function Public Shared Function GetTransactions() As AccountTransaction() Dim Transactions(28) As AccountTransaction Transactions(0) = New AccountTransaction Transactions(0).TransactionDate = New DateTime(2007, 1, 16) Transactions(0).ProcessedBy = 39850 Transactions(0).ProcessedFor = "95-722947-93" Transactions(0).TransactionType = TransactionTypes.Deposit Transactions(0).DepositAmount = 325.5 Transactions(1) = New AccountTransaction Transactions(1).TransactionDate = New DateTime(2007, 1, 18) Transactions(1).ProcessedBy = 94805 Transactions(1).ProcessedFor = "62-384638-48" Transactions(1).TransactionType = TransactionTypes.Deposit Transactions(1).DepositAmount = 550.0 Transactions(2) = New AccountTransaction Transactions(2).TransactionDate = New DateTime(2007, 1, 18) Transactions(2).ProcessedBy = 39850 Transactions(2).ProcessedFor = "92-318284-75" Transactions(2).TransactionType = TransactionTypes.Deposit Transactions(2).DepositAmount = 975.35 Transactions(3) = New AccountTransaction Transactions(3).TransactionDate = New DateTime(2007, 1, 22) Transactions(3).ProcessedBy = 94852 Transactions(3).ProcessedFor = "95-722947-93" Transactions(3).TransactionType = TransactionTypes.Withdrawal Transactions(3).WithdrawalAmount = 100.0 Transactions(4) = New AccountTransaction Transactions(4).TransactionDate = New DateTime(2007, 1, 22) Transactions(4).ProcessedBy = 70594 Transactions(4).ProcessedFor = "62-384638-48" Transactions(4).TransactionType = TransactionTypes.Withdrawal Transactions(4).WithdrawalAmount = 122.48 Transactions(5) = New AccountTransaction Transactions(5).TransactionDate = New DateTime(2007, 1, 22) Transactions(5).ProcessedBy = 94852 Transactions(5).ProcessedFor = "92-318284-75" Transactions(5).TransactionType = TransactionTypes.Withdrawal Transactions(5).WithdrawalAmount = 214.86 Transactions(6) = New AccountTransaction Transactions(6).TransactionDate = New DateTime(2007, 1, 22) Transactions(6).ProcessedBy = 85285 Transactions(6).ProcessedFor = "62-384638-48" Transactions(6).TransactionType = TransactionTypes.Withdrawal Transactions(6).WithdrawalAmount = 140.0 Transactions(7) = New AccountTransaction Transactions(7).TransactionDate = New DateTime(2007, 1, 24) Transactions(7).ProcessedBy = 85285 Transactions(7).ProcessedFor = "95-722947-93" Transactions(7).TransactionType = TransactionTypes.MoneyOrder Transactions(7).WithdrawalAmount = 116.24 Transactions(8) = New AccountTransaction Transactions(8).TransactionDate = New DateTime(2007, 1, 24) Transactions(8).ProcessedFor = "95-722947-93" Transactions(8).TransactionType = TransactionTypes.TransactionFee Transactions(8).ChargeAmount = 1.45 Transactions(9) = New AccountTransaction Transactions(9).TransactionDate = New DateTime(2007, 1, 30) Transactions(9).ProcessedBy = 70594 Transactions(9).ProcessedFor = "62-384638-48" Transactions(9).TransactionType = TransactionTypes.Withdrawal Transactions(9).WithdrawalAmount = 40.0 Transactions(10) = New AccountTransaction Transactions(10).TransactionDate = New DateTime(2007, 1, 30) Transactions(10).ProcessedFor = "95-722947-93" Transactions(10).TransactionType = TransactionTypes.MonthlyCharge Transactions(10).ChargeAmount = 6.0 Transactions(11) = New AccountTransaction Transactions(11).TransactionDate = New DateTime(2007, 1, 30) Transactions(11).ProcessedFor = "92-318284-75" Transactions(11).TransactionType = TransactionTypes.MonthlyCharge Transactions(11).ChargeAmount = 6.0 Transactions(12) = New AccountTransaction Transactions(12).TransactionDate = New DateTime(2007, 1, 30) Transactions(12).ProcessedFor = "62-384638-48" Transactions(12).TransactionType = TransactionTypes.MonthlyCharge Transactions(12).ChargeAmount = 6.0 Transactions(13) = New AccountTransaction Transactions(13).TransactionDate = New DateTime(2007, 2, 6) Transactions(13).ProcessedBy = 85285 Transactions(13).ProcessedFor = "92-318284-75" Transactions(13).TransactionType = TransactionTypes.Withdrawal Transactions(13).WithdrawalAmount = 42.35 Transactions(14) = New AccountTransaction Transactions(14).TransactionDate = New DateTime(2007, 2, 6) Transactions(14).ProcessedBy = 70594 Transactions(14).ProcessedFor = "95-722947-93" Transactions(14).TransactionType = TransactionTypes.Withdrawal Transactions(14).WithdrawalAmount = 115.0 Transactions(15) = New AccountTransaction Transactions(15).TransactionDate = New DateTime(2007, 2, 6) Transactions(15).ProcessedBy = 94852 Transactions(15).ProcessedFor = "62-384638-48" Transactions(15).TransactionType = TransactionTypes.Withdrawal Transactions(15).WithdrawalAmount = 64.14 Transactions(16) = New AccountTransaction Transactions(16).TransactionDate = New DateTime(2007, 2, 28) Transactions(16).ProcessedFor = "95-722947-93" Transactions(16).TransactionType = TransactionTypes.MonthlyCharge Transactions(16).ChargeAmount = 6.0 Transactions(17) = New AccountTransaction Transactions(17).TransactionDate = New DateTime(2007, 2, 28) Transactions(17).ProcessedFor = "95-722947-93" Transactions(17).TransactionType = TransactionTypes.Overdraft Transactions(17).WithdrawalAmount = 35.0 Transactions(18) = New AccountTransaction Transactions(18).TransactionDate = New DateTime(2007, 2, 28) Transactions(18).ProcessedFor = "62-384638-48" Transactions(18).TransactionType = TransactionTypes.MonthlyCharge Transactions(18).ChargeAmount = 6.0 Transactions(19) = New AccountTransaction Transactions(19).TransactionDate = New DateTime(2007, 2, 28) Transactions(19).ProcessedFor = "92-318284-75" Transactions(19).TransactionType = TransactionTypes.MonthlyCharge Transactions(19).ChargeAmount = 6.0 Transactions(20) = New AccountTransaction Transactions(20).TransactionDate = New DateTime(2007, 3, 15) Transactions(20).ProcessedBy = 70594 Transactions(20).ProcessedFor = "95-722947-93" Transactions(20).TransactionType = TransactionTypes.Withdrawal Transactions(20).WithdrawalAmount = 200.0 Transactions(21) = New AccountTransaction Transactions(21).TransactionDate = New DateTime(2007, 3, 26) Transactions(21).ProcessedBy = 39850 Transactions(21).ProcessedFor = "17-490040-83" Transactions(21).TransactionType = TransactionTypes.Deposit Transactions(21).DepositAmount = 1000.0 Transactions(22) = New AccountTransaction Transactions(22).TransactionDate = New DateTime(2007, 4, 4) Transactions(22).ProcessedBy = 74228 Transactions(22).ProcessedFor = "58-405048-15" Transactions(22).TransactionType = TransactionTypes.Deposit Transactions(22).DepositAmount = 126.85 Transactions(23) = New AccountTransaction Transactions(23).TransactionDate = New DateTime(2007, 4, 6) Transactions(23).ProcessedBy = 85285 Transactions(23).ProcessedFor = "92-318284-75" Transactions(23).TransactionType = TransactionTypes.Deposit Transactions(23).DepositAmount = 250.0 Transactions(24) = New AccountTransaction Transactions(24).TransactionDate = New DateTime(2007, 4, 6) Transactions(24).ProcessedBy = 70594 Transactions(24).ProcessedFor = "62-384638-48" Transactions(24).TransactionType = TransactionTypes.Deposit Transactions(24).DepositAmount = 400.0 Transactions(25) = New AccountTransaction Transactions(25).TransactionDate = New DateTime(2007, 4, 12) Transactions(25).ProcessedBy = 94852 Transactions(25).ProcessedFor = "95-722947-93" Transactions(25).TransactionType = TransactionTypes.Deposit Transactions(25).DepositAmount = 100.0 Transactions(25) = New AccountTransaction() Transactions(25).TransactionDate = New DateTime(2007, 4, 30) Transactions(25).ProcessedFor = "58-405048-15" Transactions(25).TransactionType = TransactionTypes.MonthlyCharge Transactions(25).ChargeAmount = 6.0 Transactions(26) = New AccountTransaction Transactions(26).TransactionDate = New DateTime(2007, 4, 30) Transactions(26).ProcessedFor = "62-384638-48" Transactions(26).TransactionType = TransactionTypes.MonthlyCharge Transactions(26).ChargeAmount = 6.0 Transactions(27) = New AccountTransaction() Transactions(27).TransactionDate = New DateTime(2007, 4, 30) Transactions(27).ProcessedFor = "92-318284-75" Transactions(27).TransactionType = TransactionTypes.MonthlyCharge Transactions(27).ChargeAmount = 6.0 Transactions(28) = New AccountTransaction() Transactions(28).TransactionDate = New DateTime(2007, 4, 30) Transactions(28).ProcessedFor = "17-490040-83" Transactions(28).TransactionType = TransactionTypes.MonthlyCharge Transactions(28).ChargeAmount = 6.0 Return Transactions End Function End Class

24. Access the Central form and a button to it
25. Change the properties of the button as follows:
    (Name): btnEmployees
    Text:     Employees
26. Double-click the Employees button and implement its event as follows:
     

    Private Sub btnEmployees_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles btnEmployees.Click Dim i As Integer Dim frmEmployees As Employees = New Employees Dim StaffMembers() As Employee = AccountsRecords.GetEmployees() frmEmployees.lvwEmployees.Items.Clear() i = 1 For Each empl As Employee In StaffMembers Dim lviEmployee As ListViewItem = New ListViewItem(i) lviEmployee.SubItems.Add(CStr(empl.EmployeeNumber)) lviEmployee.SubItems.Add(empl.FirstName) lviEmployee.SubItems.Add(empl.LastName) lviEmployee.SubItems.Add(empl.FullName) lviEmployee.SubItems.Add(empl.Title) lviEmployee.SubItems.Add(empl.HourlySalary.ToString("F")) frmEmployees.lvwEmployees.Items.Add(lviEmployee) i = i + 1 Next frmEmployees.ShowDialog() End Sub

27. Return to the Central form and a button to it
28. Change the properties of the button as follows:
    (Name): btnCustomers
    Text:     Customers
29. Double-click the Employees button and implement its event as follows:
     

    Private Sub btnCustomers_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles btnCustomers.Click Dim i As Integer Dim frmCustomers As Customers = New Customers Dim Clients() As Customer = AccountsRecords.GetCustomers() frmCustomers.lvwCustomers.Items.Clear() i = 1 For Each client As Customer In Clients Dim lviCustomer As ListViewItem = New ListViewItem(i) lviCustomer.SubItems.Add(client.CreatedBy) lviCustomer.SubItems.Add(client.DateCreated.ToShortDateString()) lviCustomer.SubItems.Add(client.CustomerName) lviCustomer.SubItems.Add(client.AccountNumber) lviCustomer.SubItems.Add(client.AccountType) lviCustomer.SubItems.Add(client.Status.ToString()) frmCustomers.lvwCustomers.Items.Add(lviCustomer) i = i + 1 Next frmCustomers.ShowDialog() End Sub

30. Return to the Central form and a button to it
31. Change the properties of the button as follows:
    (Name): btnTransactions
    Text:     Transactions
32. Double-click the Employees button and implement its event as follows:
     

    Private Sub btnTransactions_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) _ Handles btnTransactions.Click Dim i As Integer Dim frmTransactions As CustomersTransactions = _ New CustomersTransactions Dim Transactions() As AccountTransaction = _ AccountsRecords.GetTransactions() frmTransactions.lvwTransactions.Items.Clear() i = 1 For Each ActTrans As AccountTransaction In Transactions Dim lviTransactions As ListViewItem = New ListViewItem(i) lviTransactions.SubItems.Add( _ ActTrans.TransactionDate.ToString("dd-MMM-yyyy")) If ActTrans.ProcessedBy = 0 Then lviTransactions.SubItems.Add("") Else lviTransactions.SubItems.Add(ActTrans.ProcessedBy) End If lviTransactions.SubItems.Add(ActTrans.ProcessedFor) lviTransactions.SubItems.Add(ActTrans.TransactionType.ToString()) If ActTrans.DepositAmount = 0 Then lviTransactions.SubItems.Add("") Else lviTransactions.SubItems.Add( _ ActTrans.DepositAmount.ToString("F")) End If If ActTrans.WithdrawalAmount = 0 Then lviTransactions.SubItems.Add("") Else lviTransactions.SubItems.Add( _ ActTrans.WithdrawalAmount.ToString("F")) End If If ActTrans.ChargeAmount = 0 Then lviTransactions.SubItems.Add("") Else lviTransactions.SubItems.Add( _ ActTrans.ChargeAmount.ToString("F")) End If frmTransactions.lvwTransactions.Items.Add(lviTransactions) i = i + 1 Next frmTransactions.ShowDialog() End Sub

33. Execute the application to see the results
34. Close the forms and return to your programming environment

Because an array is primarily a series of objects or values, there are various pieces of information you would get interested to get from it. Typical operations include:

• Adding elements to the array
• Re-arranging the list or the order of elements in the array.
• Finding out whether the array contains a certain element
• If the array contains a certain element, what index that element has

Although you can write your own routines to perform these operations, the Array class provides most of the methods you would need to get the necessary information.

1. To create a new form, on the main menu, click Project -> Add Windows Form
2. Set the name to CustomerTransactions and press Enter
3. Design the form as follows:
    

   Control Text Name Other Properties Label View Transactions For:     MaskedTextBox   txtAccountNumber Mask: 00-000000-00 Button Find btnFind   ListView   lvwCustomers FullRowSelect: True GridLines: True View: Details Columns (Name) Text TextAlign Width colIndex #   25 colTransactionDate Trans Date Center 80 colProcessedBy Processed By Center 80 colTransactionType Trans Type   90 colDeposit Deposit Right   colWithdrawal Withdrawal Right 65 colChargeAmount Charge Right 50 Button Close btnClose

4. Save all

We have seen that, using the () operator, you can add a new element to an array. Still, to support this operation, the Array class is equipped with the SetValue() method that is overloaded with various versions. Here is an example that adds an element to the third position of the array:

Public Class Exercise
    Dim People(7) As Person

    Private Sub ArrayInitializer() 

        For i As Integer = 0 To 7
            People(i) = New Person
            People(i).PersonID = 0
            People(i).FirstName = ""
            People(i).LastName = ""
            People(i).Gender = "Unknown"
        Next

    End Sub

    Private Sub ShowPeople()
        lvwPeople.Items.Clear()

        For Each Pers As Person In People
            Dim lviPerson As ListViewItem = New ListViewItem(Pers.FirstName)

            lviPerson.SubItems.Add(Pers.LastName)
            lviPerson.SubItems.Add(Pers.Gender)

            lvwPeople.Items.Add(lviPerson)
        Next
    End Sub

    Private Sub Exercise_Load(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) Handles MyBase.Load
        ArrayInitializer()
        ShowPeople()
    End Sub

    Private Sub btnAdd_Click(ByVal sender As Object, _
                             ByVal e As System.EventArgs) Handles btnAdd.Click
        Dim pers As Person = New Person

        pers.PersonID = CInt(txtPersonID.Text)
        pers.FirstName = txtFirstName.Text
        pers.LastName = txtLastName.Text
        pers.Gender = cbxGenders.Text

        People.SetValue(pers, 2)
        ShowPeople()
    End Sub
End Class

When the Array.SetValue() method is called, it replaces the element at the indicated position.

The reverse of adding an item to an array is to retrieve one. To support this operation, the Array class is equipped with the GetValue() method that comes in various versions. Here is an example of calling it:

Public Class Exercise
    Dim People(7) As Person

    Private Sub Exercise_Load(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) Handles MyBase.Load
        People(0) = New Person(72947, "Paulette", _
                               "Cranston", "Female")
        People(1) = New Person(70854, "Harry", _
                               "Kumar", "Male")
        People(2) = New Person(27947, "Jules", _
                               "Davidson", "Male")
        People(3) = New Person(62835, "Leslie", _
                               "Harrington", "Unknown")
        People(4) = New Person(92958, "Ernest", _
                              "Colson", "Male")
        People(5) = New Person(91749, "Patricia", _
                              "Katts", "Female")
        People(6) = New Person(29749, "Patrice", _
                              "Abanda", "Unknown")
        People(7) = New Person(24739, "Frank", _
                              "Thomasson", "Male")

        For i As Integer = 0 To People.Length - 1
            Dim lviPerson As ListViewItem = New ListViewItem(People(i).FirstName)

            lviPerson.SubItems.Add(People(i).LastName)
            lviPerson.SubItems.Add(People(i).Gender)

            lvwPeople.Items.Add(lviPerson)
        Next
    End Sub

    Private Sub lvwPeople_ItemSelectionChanged(ByVal sender As Object, _
       ByVal e As System.Windows.Forms.ListViewItemSelectionChangedEventArgs) _
                                               Handles lvwPeople.ItemSelectionChanged
        Dim pers As Person = CType(People.GetValue(e.ItemIndex), Person)

        txtPersonID.Text = pers.PersonID
        txtFirstName.Text = pers.FirstName
        txtLastName.Text = pers.LastName
        cbxGenders.Text = pers.Gender
    End Sub

End Class

When calling this method, make sure you provide a valid index, if you do not, you would get an IndexOutOfRangeException exception.

Once some elements have been added to an array, you can try to locate one. One of the most fundamental means of looking for an item consists of finding out whether a certain element exists in the array. To support this operation, the Array class is equipped with the Exists() method whose syntax is:

Public Shared Function Exists(Of T) ( _
	array As T(), _
	match As Predicate(Of T) _
) As Boolean

This is a generic method that takes two arguments. The first is the array on which you will look for the item. The second argument is a delegate that specifies the criterion to apply. Here is an example:

Public Class Exercise
    Dim People(7) As Person
    Shared IDToFind As Integer

    Private Sub Exercise_Load(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) Handles MyBase.Load
        . . . No Change
    End Sub

    Private Shared Function IDExists(ByVal p As Person) As Boolean
        If p.PersonID = IDToFind Then
            Return True
        Else
            Return False
        End If
    End Function

    Private Sub btnExists_Click(ByVal sender As System.Object, _
                                ByVal e As System.EventArgs) Handles btnExists.Click
        IDToFind = CInt(txtPersonID.Text)

        If Array.Exists(People, AddressOf IDExists) Then
            MessageBox.Show("The person was found")
        Else
            MessageBox.Show("The person was not found anywhere")
        End If
    End Sub
End Class

1. On the Account Transactions form, double-click the Find button and change the file as follows:
    

   Public Class CustomerTransactions Shared AccountNumber As String Private Shared Function AccountNumberExists(ByVal Client As Customer) _ As Boolean If Client.AccountNumber = AccountNumber Then Return True Else Return False End If End Function Private Sub btnFind_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) _ Handles btnFind.Click AccountNumber = txtAccountNumber.Text Dim Accounts() As Customer = AccountsRecords.GetCustomers() If Array.Exists(Accounts, AddressOf AccountNumberExists) Then MsgBox("Good") Else MsgBox("There is no customer with that account number") End If End Sub End Class

2. Display the Central form and complete its design as follows:
    

   Button Text Name Employees btnEmployees Customers btnCustomers Transactions btnTransactions Customer Records btnCustomerRecords Close btnClose

3. Double-click the Customer Records button and implement its event as follows:
    

   Private Sub btnCustomerRecords_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnCustomerRecords.Click Dim CustRecords As CustomerTransactions = New CustomerTransactions CustRecords.ShowDialog() End Sub

4. Return to the Central form and double-click the Close button
5. Implement its event as follows:
    

   Private Sub btnClose_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) Handles btnClose.Click End End Sub

6. Execute the application to test it
7. Close the forms and return to your programming environment

One of the most valuable operations you can perform on an array consists of looking for a particular element. To assist you with this, the Array class is equipped with the Find() method. Its syntax is:

Public Shared Function Find(Of T) ( _
	array As T(), _
	match As Predicate(Of T) _
) As T

This generic method takes two arguments. The first argument is the name of the array that holds the elements. The second argument is a delegate that has the criterion to be used to find the element. Here is an example:

Private Sub btnFind_Click(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) Handles btnFind.Click
        IDToFind = CInt(txtPersonID.Text)

        Dim pers As Person = Array.Find(People, AddressOf IDExists)

        If Not pers Is Nothing Then
            txtFirstName.Text = pers.FirstName
            txtLastName.Text = pers.LastName
            cbxGenders.Text = pers.Gender
        End If
End Sub

1. Access the CustomerTransactions.cs source code and change the Click event of the Find button as follows:
    

   Private Sub btnFind_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles btnFind.Click ' AccountNumber = txtAccountNumber.Text ' Dim Accounts() As Customer = AccountsRecords.GetCustomers() ' If Array.Exists(Accounts, AddressOf AccountNumberExists) Then ' MsgBox("Good") ' Else ' MsgBox("There is no customer with that account number") ' End If Dim TotalDeposits As Double = 0 Dim TotalWithdrawals As Double = 0 Dim TotalCharges As Double = 0 Dim Balance As Double AccountNumber = txtAccountNumber.Text Dim Accounts() As Customer = AccountsRecords.GetCustomers() Dim Trans() As AccountTransaction = _ AccountsRecords.GetTransactions() Dim AccountFound As Boolean = _ Array.Exists(Accounts, AddressOf AccountNumberExists) If AccountFound = True Then Dim i As Integer = 1 lvwTransactions.Items.Clear() For Each ActTrans As AccountTransaction In Trans If ActTrans.ProcessedFor = AccountNumber Then Dim lviTransactions As ListViewItem = New ListViewItem(i) lviTransactions.SubItems.Add( _ ActTrans.TransactionDate.ToString("dd-MMM-yyyy")) If ActTrans.ProcessedBy = 0 Then lviTransactions.SubItems.Add("") Else lviTransactions.SubItems.Add(ActTrans.ProcessedBy) End If lviTransactions.SubItems.Add( _ ActTrans.TransactionType.ToString()) If ActTrans.DepositAmount = 0 Then lviTransactions.SubItems.Add("") Else lviTransactions.SubItems.Add( _ ActTrans.DepositAmount.ToString("F")) End If If ActTrans.WithdrawalAmount = 0 Then lviTransactions.SubItems.Add("") Else lviTransactions.SubItems.Add( _ ActTrans.WithdrawalAmount.ToString("F")) End If If ActTrans.ChargeAmount = 0 Then lviTransactions.SubItems.Add("") Else lviTransactions.SubItems.Add( _ ActTrans.ChargeAmount.ToString("F")) End If lvwTransactions.Items.Add(lviTransactions) i = i + 1 End If Next For Each lviTransaction As ListViewItem In lvwTransactions.Items If lviTransaction.SubItems(4).Text <> "" Then TotalDeposits = TotalDeposits + _ CDbl(lviTransaction.SubItems(4).Text) End If If lviTransaction.SubItems(5).Text <> "" Then TotalWithdrawals = TotalWithdrawals + _ CDbl(lviTransaction.SubItems(5).Text) End If If lviTransaction.SubItems(6).Text <> "" Then TotalCharges = TotalCharges + _ CDbl(lviTransaction.SubItems(6).Text) End If Next Balance = TotalDeposits - (TotalWithdrawals + TotalCharges) txtTotalDeposits.Text = FormatNumber(TotalDeposits) txtTotalWithdrawals.Text = FormatNumber(TotalWithdrawals) txtTotalCharges.Text = FormatNumber(TotalCharges) txtBalance.Text = FormatNumber(Balance) Else MessageBox.Show("There is no customer with that account number") End If End Sub

2. In the Class Name combo box, select btnClose
3. In the Method Name combo box, select Click and implement the event as follows:
    

   Private Sub btnClose_Click(ByVal sender As Object, _ ByVal e As System.EventArgs) _ Handles btnClose.Click Close() End Sub

4. Execute the application to test it