An Array of Values

8/10/2019 An Array of Values

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An Array of Values

Introduction

A database is a list of values. The values can be organized to make it easy to retrieve and optionally

manipulate them. A computer database is a list of values that are stored in the computer, usually asone or more files. The values can then be accessed when needed. Probably the most fundamentaltype of list of values can be created, and managed, as an array.

Practical Learning: Introducing Databases

1. Start Microsoft Visual Basic and create a Windows Forms Application named

NationalBank12. In the Solution Explorer, right-click Form1.vb and click Rename

3. Type Central.vband press Enter

Creating an Array

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.LoadDim 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:


ByVal e As System.EventArgs) Handles Me.LoadDim 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))

NextEnd Sub


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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 youcan create your own class. Here is an example:

Public Class PersonPublic PersonID As IntegerPublic FirstName As String

Public LastName As StringPublic 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 = LNameGender = Gdr

End Sub

End Class

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


ByVal e As System.EventArgs) Handles Me.LoadDim 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 7Dim lviPerson As ListViewItem = New ListViewItem(People(i).FirstName)

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

lvwPeople.Items.Add(lviPerson)


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NextEnd Sub

The Array Class

To assist you with creating or managing arrays, the .NET Framework provides the Arrayclass. Everyarray 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 Arrayclass, 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 Lengthproperty 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 elementsthat the array will contain. You must do this especially if you declare the variable without initializing

the array. Here is an example:


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:


ByVal e As System.EventArgs) Handles Me.LoadDim People(4) As Person


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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. Thiswould produce an IndexOutOfRangeExcceptionexception:

One of the most valuable features of the Arrayclass is that it allows an array to be "resizable". Thatis, 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 ofthe 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", _


"Davidson", "Male")

People(3) = New Person(62835, "Leslie", _"Harrington", "Unknown")

People(4) = New Person(92958, "Ernest", _"Colson", "Male")


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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 - 1Dim lviPerson As ListViewItem = New ListViewItem(People(i).FirstName)




NextEnd Sub

End Class

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

An Array as a Field

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, youcan declare an array as a member of a class. Here is an example:


Dim People() As PersonEnd Class

The advantage of this approach is that you can access the array from any member of the same class oreven 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 Loadevent of a form. After initializing the array,you can then access in another method or another event of the form. Here is an example:


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", _


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"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")





NextEnd Sub

End Class

Arrays and Methods

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


Private Sub ArrayInitializer(ByVal People() As Person)

End SubEnd Class

In the method, you can use the array as you see fit. For example you can assign values to the elementsof 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:


Private Sub ArrayInitializer(ByVal People() As Person)People(0) = New Person(72947, "Paulette", _

"Cranston", "Female")People(1) = New Person(70854, "Harry", _


"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


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Private Sub ShowPeople(ByVal People() As Person)For i As Integer = 0 To People.Length - 1





End Sub

Private Sub Exercise_Load(ByVal sender As System.Object, _

ByVal e As System.EventArgs) Handles MyBase.LoadDim Persons(7) As Person

ArrayInitializer(Persons)ShowPeople(Persons)

End SubEnd 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 ExercisePrivate FunctionArrayInitializer() As Person()





"Davidson", "Male")People(3) = New Person(62835, "Leslie", _

"Harrington", "Unknown")


People(5) = New Person(91749, "Patricia", _

"Katts", "Female")People(6) = New Person(29749, "Patrice", _

"Abanda", "Unknown")People(7) = New Person(24739, "Frank", _


Return PeopleEnd Function

Private Sub ShowPeople(ByVal People() As Person)For i As Integer = 0 To People.Length - 1





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Next

End Sub


ByVal e As System.EventArgs) Handles MyBase.LoadDim Persons(7) As Person

Persons = ArrayInitializer()

ShowPeople(Persons)End Sub

End Class

Practical Learning: Creating an Array

1. To create a new class, on the main menu, click Project -> Add Class...2. Set the name to Employeeand press Enter

3. Complete the file as follows:

Public Class Employee

Public EmployeeNumber As IntegerPublic FirstName As String

Public LastName As StringPublic Title As StringPublic CanCreateNewAccount As Boolean

Public HourlySalary As Double

Public ReadOnly Property FullName() As StringGet

Return LastName & ", " & FirstName

End GetEnd 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 Employeesand press Enter

6. Design the form as follows:


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Control Text Name Other Properties

ListView lvwEmployees

FullRowSelect: True

GridLines: True

View: Details

Columns

(Name) Text TextAlignWidth

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 Customerand press Enter

9. Complete the file as follows:

Public Enum AccountStatus

Active

SuspendedClosed

End Enum

Public Class CustomerPublic CreatedBy As StringPublic DateCreated As DateTime

Public CustomerName As String

Public AccountNumber As String

Public AccountType As String


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Public Status As AccountStatusEnd 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 Customersand press Enter12.Design the form as follows:


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


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) HandlesbtnClose.Click

Close()

End Sub


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14.To create a new class, on the main menu, click Project -> Add Class...15.Set the name to AccountTransactionand press Enter

16.Complete the file as follows:

Public Enum TransactionTypesDeposit

WithdrawalTransferMonthlyCharge

MoneyOrderOverdraft

TransactionFeeEnd Enum

Public Class AccountTransactionPublic TransactionDate As DateTime

Public ProcessedBy As IntegerPublic ProcessedFor As StringPublic TransactionType As TransactionTypes

Public DepositAmount As Double

Public WithdrawalAmount As Double

Public ChargeAmount As DoubleEnd 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 Form18.Set the name to CustomersTransactionsand press Enter

19.Design the form as follows:


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ListView lvwTransactionsFullRowSelect: TrueGridLines: 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 RightcolWithdrawalAmount Withdrawal Right 65

colChargeAmount Charge Right 50


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


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Private Sub btnClose_Click(ByVal sender As System.Object, _

ByVal e As System.EventArgs) Handles

btnClose.ClickClose()

End Sub

21.To create a new class, on the main menu, click Project -> Add Class...

22.Set the name to AccountsRecordsand press Enter23.Complete the file as follows:

Public Class AccountsRecords

Public Shared Function GetEmployees() As Employee()Dim StaffMembers(6) As Employee

StaffMembers(0) = New EmployeeStaffMembers(0).EmployeeNumber = 74228

StaffMembers(0).FirstName = "Chrissie"StaffMembers(0).LastName = "Nomads"

StaffMembers(0).Title = "General Manager"StaffMembers(0).CanCreateNewAccount = TrueStaffMembers(0).HourlySalary = 40.25

StaffMembers(1) = New Employee

StaffMembers(1).EmployeeNumber = 27905StaffMembers(1).FirstName = "Calvin"StaffMembers(1).LastName = "Braxton"

StaffMembers(1).Title = "Public Relations Manager"

StaffMembers(1).CanCreateNewAccount = FalseStaffMembers(1).HourlySalary = 25.95

StaffMembers(2) = New Employee()

StaffMembers(2).EmployeeNumber = 94805StaffMembers(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 = 39850StaffMembers(3).FirstName = "Walter"

StaffMembers(3).LastName = "Lemme"StaffMembers(3).Title = "Accounts Manager"

StaffMembers(3).CanCreateNewAccount = True


StaffMembers(4) = New Employee()StaffMembers(4).EmployeeNumber = 70594

StaffMembers(4).FirstName = "Cecile"StaffMembers(4).LastName = "Richards"


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StaffMembers(4).Title = "Accounts Representative"StaffMembers(4).CanCreateNewAccount = FalseStaffMembers(4).HourlySalary = 18.15


StaffMembers(5).EmployeeNumber = 85285

StaffMembers(5).FirstName = "Joan"StaffMembers(5).LastName = "Verrion"

StaffMembers(5).Title = "Accounts Representative"StaffMembers(5).CanCreateNewAccount = False



StaffMembers(6).EmployeeNumber = 94852StaffMembers(6).FirstName = "Donald"

StaffMembers(6).LastName = "Waters"StaffMembers(6).Title = "Accounts Representative"StaffMembers(6).CanCreateNewAccount = False


Return StaffMembersEnd 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"


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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 ClientsEnd 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.DepositTransactions(0).DepositAmount = 325.5



Transactions(1).ProcessedFor = "62-384638-48"

Transactions(1).TransactionType = TransactionTypes.DepositTransactions(1).DepositAmount = 550.0

Transactions(2) = New AccountTransactionTransactions(2).TransactionDate = New DateTime(2007, 1, 18)

Transactions(2).ProcessedBy = 39850Transactions(2).ProcessedFor = "92-318284-75"



Transactions(3).ProcessedBy = 94852Transactions(3).ProcessedFor = "95-722947-93"Transactions(3).TransactionType = TransactionTypes.Withdrawal

Transactions(3).WithdrawalAmount = 100.0


Transactions(4).ProcessedBy = 70594

Transactions(4).ProcessedFor = "62-384638-48"Transactions(4).TransactionType = TransactionTypes.Withdrawal






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Transactions(5).TransactionType = TransactionTypes.WithdrawalTransactions(5).WithdrawalAmount = 214.86


Transactions(6).TransactionDate = New DateTime(2007, 1, 22)

Transactions(6).ProcessedBy = 85285

Transactions(6).ProcessedFor = "62-384638-48"Transactions(6).TransactionType = TransactionTypes.Withdrawal


Transactions(7) = New AccountTransactionTransactions(7).TransactionDate = New DateTime(2007, 1, 24)Transactions(7).ProcessedBy = 85285

Transactions(7).ProcessedFor = "95-722947-93"Transactions(7).TransactionType = TransactionTypes.MoneyOrder



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).TransactionType = TransactionTypes.WithdrawalTransactions(9).WithdrawalAmount = 40.0


Transactions(10).ProcessedFor = "95-722947-93"Transactions(10).TransactionType =

TransactionTypes.MonthlyChargeTransactions(10).ChargeAmount = 6.0



TransactionTypes.MonthlyCharge




Transactions(12).TransactionType =TransactionTypes.MonthlyCharge






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Transactions(13).TransactionType =TransactionTypes.Withdrawal



Transactions(14).TransactionDate = New DateTime(2007, 2, 6)


Transactions(14).TransactionType =TransactionTypes.Withdrawal





TransactionTypes.Withdrawal


Transactions(16) = New AccountTransactionTransactions(16).TransactionDate = New DateTime(2007, 2, 28)Transactions(16).ProcessedFor = "95-722947-93"





Transactions(17).TransactionType = TransactionTypes.OverdraftTransactions(17).WithdrawalAmount = 35.0





Transactions(19) = New AccountTransactionTransactions(19).TransactionDate = New DateTime(2007, 2, 28)Transactions(19).ProcessedFor = "92-318284-75"






TransactionTypes.Withdrawal




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Transactions(21).TransactionDate = New DateTime(2007, 3, 26)Transactions(21).ProcessedBy = 39850Transactions(21).ProcessedFor = "17-490040-83"

Transactions(21).TransactionType = TransactionTypes.Deposit

Transactions(21).DepositAmount = 1000.0





Transactions(23).ProcessedBy = 85285Transactions(23).ProcessedFor = "92-318284-75"Transactions(23).TransactionType = TransactionTypes.Deposit


Transactions(24) = New AccountTransactionTransactions(24).TransactionDate = New DateTime(2007, 4, 6)Transactions(24).ProcessedBy = 70594

Transactions(24).ProcessedFor = "62-384638-48"Transactions(24).TransactionType = TransactionTypes.Deposit




Transactions(25).ProcessedFor = "95-722947-93"Transactions(25).TransactionType = TransactionTypes.DepositTransactions(25).DepositAmount = 100.0

Transactions(25) = New AccountTransaction()


Transactions(25).TransactionType =





Transactions(27) = New AccountTransaction()Transactions(27).TransactionDate = New DateTime(2007, 4, 30)




Transactions(28) = New AccountTransaction()


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Transactions(28).TransactionDate = New DateTime(2007, 4, 30)Transactions(28).ProcessedFor = "17-490040-83"Transactions(28).TransactionType =



Return TransactionsEnd Function

End Class

24.Access the Central form and a button to it

25.Change the properties of the button as follows:

(Name): btnEmployeesText: 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) HandlesbtnEmployees.Click

Dim i As Integer

Dim frmEmployees As Employees = New EmployeesDim StaffMembers() As Employee = AccountsRecords.GetEmployees()

frmEmployees.lvwEmployees.Items.Clear()

i = 1

For Each empl As Employee In StaffMembersDim 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 it28.Change the properties of the button as follows:

(Name): btnCustomers

Text: Customers29.Double-click the Employees button and implement its event as follows:


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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 ClientsDim 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 + 1Next

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: Transactions32.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 IntegerDim frmTransactions As CustomersTransactions = _

New CustomersTransactionsDim Transactions() As AccountTransaction = _

AccountsRecords.GetTransactions()

frmTransactions.lvwTransactions.Items.Clear()

i = 1

For Each ActTrans As AccountTransaction In TransactionsDim lviTransactions As ListViewItem = New ListViewItem(i)

lviTransactions.SubItems.Add( _ActTrans.TransactionDate.ToString("dd-MMM-yyyy"))


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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 ThenlviTransactions.SubItems.Add("")

ElselviTransactions.SubItems.Add( _

ActTrans.DepositAmount.ToString("F"))End If

If ActTrans.WithdrawalAmount = 0 ThenlviTransactions.SubItems.Add("")


ActTrans.WithdrawalAmount.ToString("F"))

End If

If ActTrans.ChargeAmount = 0 ThenlviTransactions.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 results34.Close the forms and return to your programming environment

Operations on an Array

Introduction

Because an array is primarily a series of objects or values, there are various pieces of information youwould 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


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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.

Practical Learning: Introducing Operations on Arrays

1. To create a new form, on the main menu, click Project -> Add Windows Form2. Set the name to CustomerTransactionsand press Enter

3. Design the form as follows:


Label View Transactions For:

MaskedTextBox txtAccountNumber Mask: 00-000000-00

Button Find btnFind

ListView lvwCustomersFullRowSelect: TrueGridLines: True

View: Details

Columns

(Name) Text TextAlignWidth

colIndex # 25

colTransactionDate Trans Date Center 80


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colProcessedBy Processed By Center 80

colTransactionType Trans Type 90

colDeposit Deposit Right

colWithdrawal Withdrawal Right 65

colChargeAmount Charge Right 50


4. Save all

Adding an Element to an Array

We have seen that, using the () operator, you can add a new element to an array. Still, to support thisoperation, 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:



Private Sub ArrayInitializer()

For i As Integer = 0 To 7

People(i) = New PersonPeople(i).PersonID = 0

People(i).FirstName = ""People(i).LastName = ""People(i).Gender = "Unknown"

Next


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End Sub

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

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

lviPerson.SubItems.Add(Pers.LastName)

lviPerson.SubItems.Add(Pers.Gender)


End Sub


ByVal e As System.EventArgs) Handles MyBase.LoadArrayInitializer()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.Textpers.LastName = txtLastName.Textpers.Gender = cbxGenders.Text

People.SetValue(pers, 2)

ShowPeople()

End SubEnd Class

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

Getting an Element From an Array

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

it:



Private Sub Exercise_Load(ByVal sender As System.Object, _ByVal e As System.EventArgs) Handles MyBase.Load





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"Davidson", "Male")People(3) = New Person(62835, "Leslie", _

"Harrington", "Unknown")


People(5) = New Person(91749, "Patricia", _

"Katts", "Female")People(6) = New Person(29749, "Patrice", _"Abanda", "Unknown")

People(7) = New Person(24739, "Frank", _



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


End Sub

Private Sub lvwPeople_ItemSelectionChanged(ByVal sender As Object, _ByVal e As System.Windows.Forms.ListViewItemSelectionChangedEventArgs) _

Handles

lvwPeople.ItemSelectionChangedDim pers As Person = CType(People.GetValue(e.ItemIndex), Person)

txtPersonID.Text = pers.PersonIDtxtFirstName.Text = pers.FirstName

txtLastName.Text = pers.LastNamecbxGenders.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 anIndexOutOfRangeExceptionexception.

Checking the Existence of an Element

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 Arrayclass 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 forthe item. The second argument is a delegate that specifies the criterion to apply. Here is an example:


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Public Class ExerciseDim People(7) As Person

Shared IDToFind As Integer


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 ThenReturn True

ElseReturn 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)ThenMessageBox.Show("The person was found")

Else

MessageBox.Show("The person was not found anywhere")End If

End SubEnd Class


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Practical Learning: Checking the Existence of an Element

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

Public Class CustomerTransactions

Shared AccountNumber As String

Private Shared Function AccountNumberExists(ByVal Client As

Customer) _As Boolean

If Client.AccountNumber = AccountNumber ThenReturn True

Else

Return FalseEnd 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


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End SubEnd Class

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

ButtonText 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)_

HandlesbtnCustomerRecords.ClickDim CustRecords As CustomerTransactions = New

CustomerTransactionsCustRecords.ShowDialog()

End Sub

4. Return to the Central form and double-click the Close button5. Implement its event as follows:


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Private Sub btnClose_Click(ByVal sender As Object, _

ByVal e As System.EventArgs) Handles

btnClose.ClickEnd

End Sub

6. Execute the application to test it

7. Close the forms and return to your programming environment

Finding an Element

One of the most valuable operations you can perform on an array consists of looking for a particularelement. 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 ThentxtFirstName.Text = pers.FirstName

txtLastName.Text = pers.LastNamecbxGenders.Text = pers.Gender

End IfEnd Sub

Practical Learning: Finding an Element

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

Private Sub btnFind_Click(ByVal sender As System.Object, _

ByVal e As System.EventArgs) HandlesbtnFind.Click

' AccountNumber = txtAccountNumber.Text

' Dim Accounts() As Customer =


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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 = 0Dim TotalCharges As Double = 0Dim 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 ThenDim i As Integer = 1

lvwTransactions.Items.Clear()

For Each ActTrans As AccountTransaction In TransIf ActTrans.ProcessedFor = AccountNumber Then

Dim lviTransactions As ListViewItem = New

ListViewItem(i)

lviTransactions.SubItems.Add( _ActTrans.TransactionDate.ToString("dd-MMM-yyyy"))

If ActTrans.ProcessedBy = 0 ThenlviTransactions.SubItems.Add("")

Else

lviTransactions.SubItems.Add(ActTrans.ProcessedBy)

End If

lviTransactions.SubItems.Add( _ActTrans.TransactionType.ToString())

If ActTrans.DepositAmount = 0 ThenlviTransactions.SubItems.Add("")


ActTrans.DepositAmount.ToString("F"))

End If

If ActTrans.WithdrawalAmount = 0 ThenlviTransactions.SubItems.Add("")

Else

lviTransactions.SubItems.Add( _ActTrans.WithdrawalAmount.ToString("F"))

End If


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If ActTrans.ChargeAmount = 0 Then

lviTransactions.SubItems.Add("")

Else

lviTransactions.SubItems.Add( _

ActTrans.ChargeAmount.ToString("F"))

End If

lvwTransactions.Items.Add(lviTransactions)

i = i + 1End If

Next

For Each lviTransaction As ListViewItem In

lvwTransactions.ItemsIf lviTransaction.SubItems(4).Text "" Then

TotalDeposits = TotalDeposits + _

CDbl(lviTransaction.SubItems(4).Text)End If

If lviTransaction.SubItems(5).Text "" ThenTotalWithdrawals = TotalWithdrawals + _


If lviTransaction.SubItems(6).Text "" Then

TotalCharges = TotalCharges + _


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 accountnumber")

End IfEnd 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


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An Array of Values

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