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11 – Arrays of Structures & Modules

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Assignment• Individual Assignment

– do not copy other people's assignment (plagiarism)

– do help each other understand lectures and tutorials (peer support)

• Backups – floppy disks – 10% failure rate– last corrupt disk 2 weeks ago

• Codes – don't show userA&E

PAS

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Session Aims & Objectives• Aims

– To introduce the idea of an array of structures– To introduce the idea of modules

• Objectives,by end of this week’s sessions, you should be able to:

– create and use an array of structures– appropriately split a program into multiple

modules

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Example 1: Employee Data• Need to keep a record of employee details

– e.g.• surname• forenames• date of birth• address• telephone number• salary

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Example 1: User Interface• Must respond to following events:

• Click Previous button: move to previous employee’s details

• Click Next button: move to next employee’s details• Type in fields: change current employee’s details

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Example 1: Code Design• 2 layers:

Layer 1Event Handler

Procedures

Layer 2General

Procedures

btnPreviousClick

btnNextClick

FormLoad

EmployeeDisplay

EmployeeStore

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Example 1: Data Design•We could use an array for each piece of employee information: Dim Surnames(1 To 10) As String Dim Forenames(1 To 10) As String Dim Salaries(1 To 10) As Double

Surnames: string

5

10

1

Forenames: string

5

10

1

Salaries: double

5

10

1

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Example 1: Employees v1Option ExplicitDim Surnames(1 To 10) As StringDim Forenames(1 To 10) As StringDim Salaries(1 To 10) As DoubleDim curEmp As Integer

Sub EmpDisplay() lblEmpNum.Caption = curEmp txtSurname.Text = Surnames(curEmp) txtForenames.Text = Forenames(curEmp) txtSalary.Text = Salaries(curEmp)End Sub

Sub EmpStore() Surnames(curEmp) = txtSurname.Text Forenames(curEmp) = txtForenames.Text Salaries(curEmp) = Val(txtSalary.Text)End Sub

Private Sub Form_Load() curEmp = 1 EmpDisplayEnd Sub

Private Sub btnNext_Click() EmpStore curEmp = curEmp + 1 EmpDisplayEnd Sub

Employees v1

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Difficulty• This design works• However, if

– all fields were implemented, and– more complex operations were added

• the code would become difficult to manage– having several separate arrays

• Arrays allow data to be grouped– however, arrays must be homogenous (same data

type)

• it would be useful to be able to group different (heterogeneous) types of data

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Structures• Groups different types of data

• Declaration of type: Type TAnimal Name As String Species As String Gender As Boolean End Type

• Use of type (in variable declaration):

Dim myPet As TAnimal• Change value of MyPet’s name:

myPet.Name = "George"

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Array of Structures

• Can also have arrays of structures:

Dim MyPets(1 To 5) As TAnimalRec• Change value:

MyPets(3).Name = "George"• Change value using index variable:

ind = 2

MyPets(ind).Name = "Fred"

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Exercise 1: Structures• Create a record definition for:

– Estate agents:House details (house num., street, price)

• Write code that will:– Create a variable of the above type

– Put data into the elements of that variable

Type THouse Num As Long Street As String Price As DoubleEnd Type

Dim myHouse As THouse

myHouse.Street = "Portland Square"

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Exercise 2: Structures• Create a record definition for:

– Police stolen car register:Car details (Reg. number, colour, model)

• Write code that will:– Create a variable of the above type

– Put data into the elements of that variable

Type TCar RegNum As String Colour As String Model As StringEnd Type

Dim myCar As TCar

myCar.RegNum = "GH23 XRB"

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Example 2: Data Design• We can now use a single array that uses a

user defined type/record/structure:

Surname: string

Employees: TEmployee

5

10

1

Salary: doubleForenames: string

each row isa TEmployee

• makes it easier to get details of single employee

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Example 2: Employees v2Option Explicit

Private Type TEmployee Surname As String Forenames As String Salary As DoubleEnd Type

Dim Employees(1 To 10) As TEmployeeDim curEmp As Integer

Sub EmpDisplay() lblEmpNum.Caption = curEmp txtSurname.Text = Employees(curEmp).Surname txtForenames.Text = Employees(curEmp).Forenames txtSalary.Text = Employees(curEmp).SalaryEnd Sub

Sub EmpStore()

Employees(curEmp).Surname = txtSurname.Text Employees(curEmp).Forenames = txtForenames.Text Employees(curEmp).Salary = Val(txtSalary.Text)End Sub

Private Sub Form_Load() curEmp = 1 EmpDisplayEnd Sub

Private Sub btnNext_Click() EmpStore curEmp = curEmp + 1 EmpDisplayEnd Sub

Employees v2

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Multiple Modules Forms• Projects can contain many modules/units

– form modules (*.FRM)• Click the Project menu• Click the Add Form menu item

– code modules (*.BAS)• Click the Project menu• Click the Add Module menu item

• Modules– divide your code into separate parts– available to other forms and code modules

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Multiple Forms: Start Form• To set the start form:

– Click the Project menu– Click the Properties menu item– Click the General tab– Click the Start up object list– Select a form

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Public & Private• Private – can only be used in current

module

• Public – can be used by any module

• Used for:– module level variables (instead of dim) Private x As Integer

– procedures and functions (start of declaration) Private Sub Display() … End Sub

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Example 3: Employees v3

Employees v3

Option Explicit

Private Sub Form_Load() curEmp = 1 EmpDisplayEnd Sub

Private Sub btnNext_Click() EmpStore curEmp = curEmp + 1 EmpDisplayEnd Sub

Option Explicit

Private Type TEmployee Surname As String Forenames As String Salary As DoubleEnd Type

Dim Employees(1 To 10) As TEmployeePublic curEmp As Integer

Sub EmpDisplay() frmMain.lblEmpNum.Caption = curEmp frmMain.txtSurname.Text = Employees(curEmp).Surname frmMain.txtForenames.Text = Employees(curEmp).Forenames frmMain.txtSalary.Text = Employees(curEmp).SalaryEnd Sub

Sub EmpStore() Employees(curEmp).Surname = frmMain.txtSurname.Text Employees(curEmp).Forenames = frmMain.txtForenames.Text Employees(curEmp).Salary = Val(frmMain.txtSalary.Text)End Sub

frmMain modEmployees

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Example 4: Multiple Forms

Option Explicit

Sub cmdSecond_Click () frmSecond.Show 1End Sub

Option ExplicitDim num As Integer

Sub cmdAdd_Click () num = num + 5End Sub

Sub cmdHide_Click () frmSecond.HideEnd Sub

Sub cmdNum_Click () picNum.Cls picNum.Print numEnd Sub

Sub cmdUnload_Click () Unload frmSecondEnd Sub

Sub Form_Load () txtSecond = "" num = 12End Sub

• Show method – displays form

• Hide method – hides form

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Modules: Sharing• Can share modules between projects:

– Click the File menu– Click the Add File menu item– Select the module file– Press the [Return] key

Project A Project B

Form 1 Form 2 Module 2 Form 4Form 3Module 1