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9 – Procedures

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Session Aims & Objectives• Aims

– To introduce the main concepts involved in grouping instructions, to deal with large programs.

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

– define procedures, and– call procedures

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Large Programs• Real programs get very large

• Exponential increase in effort

A B

C D

1 (A) 3 (A, B, AB) 6 (A, B, C, AB, AC, BC)

10 (A, B, C, D, AB, AC, BC, AD, BD, CD)

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General Procedures (what?)• Group of ordered instructions

• Identified by unique name

• Almost all computer code procedures– mirror real life procedures

Making a cup of tea: 1. Fill the kettle with water 2. Plug the kettle in 3. Switch the kettle on 4. Wait for the kettle to boil 5. Put a tea bag into the cup 6. Add sugar to the cup 7. Stir 8. Add milk to the cup 9. Stir 10. Take the tea bag out

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General Procedures (why?)• Code reuse:

same code used in many places (reduces duplication)

• Break up long code:large chunks of code are difficult to understand and maintain

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General Procedures (how)• Definition: Sub name() [Statementblock] End Sub

• Call: name

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Procedures

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Questions: Procedures• Write a line of code that calls the following

procedure: Sub Thing()

x = 24

End Sub

• Add lines of code around the following code to define a procedure:

picMain.Cls

picMain.Circle (800,800), 100

Thing

Sub Circ()

End Sub

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Example: Hotel Rooms v1

Option ExplicitConst RoomCost = 32.5Dim Rooms As IntegerDim Nights As IntegerDim TotalCost As Single

Private Sub btnCalc_Click() Rooms = Val(txtRooms.Text) Nights = Val(txtNights.Text)

TotalCost = Rooms * Nights * RoomCost

lblCost.Caption = "£" & TotalCostEnd Sub

Input

Process

Output

Hotel Rooms v1

result of operations should be visible immediately!Shneiderman 1998, p. 205

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Example: Hotel Rooms v2Option ExplicitConst RoomCost = 32.5Dim Rooms As IntegerDim Nights As IntegerDim TotalCost As Single

Private Sub Form_Load() Rooms = Val(txtRooms.Text) Nights = Val(txtNights.Text) TotalCost = Rooms * Nights * RoomCost lblCost.Caption = "£" & TotalCostEnd Sub

Private Sub txtRooms_Change() Rooms = Val(txtRooms.Text) Nights = Val(txtNights.Text) TotalCost = Rooms * Nights * RoomCost lblCost.Caption = "£" & TotalCostEnd Sub

Private Sub txtNights_Change() Rooms = Val(txtRooms.Text) Nights = Val(txtNights.Text) TotalCost = Rooms * Nights * RoomCost lblCost.Caption = "£" & TotalCostEnd SubHotel Rooms v2

Duplicate

Duplicate

Duplicate

23 lines

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Example: Hotel Rooms v3Option ExplicitConst RoomCost = 32.5Dim Rooms As IntegerDim Nights As IntegerDim TotalCost As Single

Private Sub Calculate() Rooms = Val(txtRooms.Text) Nights = Val(txtNights.Text) TotalCost = Rooms * Nights * RoomCost lblCost.Caption = "£" & TotalCostEnd Sub

Private Sub Form_Load() CalculateEnd Sub

Private Sub txtRooms_Change() CalculateEnd Sub

Private Sub txtNights_Change() CalculateEnd Sub

DuplicateCalls,not Code

Hotel Rooms v320 lines

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Example: Face v2Private Sub btnDraw_Click() picFace.Cls picFace.Circle (2400, 2400), 2000 If chkNose.Value = vbChecked Then picFace.Line (2400, 2200)-Step(0, 600) End If If optOpen.Value = True Then picFace.Circle (1600, 1600), 500 picFace.Circle (3200, 1600), 500 Else picFace.Line (1100, 1600)-Step(1000, 0) picFace.Line (2700, 1600)-Step(1000, 0) End If If optHappy.Value = True Then picFace.Circle (2400, 2400), 1200, , 3.4, 6 Else picFace.Circle (2400, 4400), 1200, , 0.6, 2.5 End IfEnd Sub

Face v2

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Example: Face v3Private Sub DrawFace() picFace.Cls picFace.Circle (2400, 2400), 2000

If chkNose.Value = vbChecked Then picFace.Line (2400, 2200)-Step(0, 600) End If

If optOpen.Value = True Then picFace.Circle (1600, 1600), 500 picFace.Circle (3200, 1600), 500 Else picFace.Line (1100, 1600)-Step(1000, 0) picFace.Line (2700, 1600)-Step(1000, 0) End If

If optHappy.Value = True Then picFace.Circle (2400, 2400), 1200, , 3.4, 6 Else picFace.Circle (2400, 4400), 1200, , 0.6, 2.5 End If

End Sub

Private Sub Form_Load() Me.Show DrawFaceEnd Sub

Private Sub chkNose_Click() DrawFaceEnd Sub

Private Sub optHappy_Click() DrawFaceEnd Sub

Private Sub optOpen_Click() DrawFaceEnd Sub

Face v3

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Example: Face v4Private Sub DrawFace() picFace.Cls picFace.Circle (2400, 2400), 2000

DrawNose DrawEyes DrawMouthEnd Sub

Private Sub DrawNose() If chkNose.Value = vbChecked Then picFace.Line (2400, 2200)-Step(0, 600) End If

End Sub

Private Sub DrawEyes() If optOpen.Value = True Then picFace.Circle (1600, 1600), 500 picFace.Circle (3200, 1600), 500 Else picFace.Line (1100, 1600)-Step(1000, 0) picFace.Line (2700, 1600)-Step(1000, 0) End If

End Sub

Private Sub DrawMouth() If optHappy.Value = True Then picFace.Circle (2400, 2400), 1200, , 3.4, 6 Else picFace.Circle (2400, 4400), 1200, , 0.6, 2.5 End If

End Sub

Private Sub Form_Load() Me.Show DrawFaceEnd Sub

…

Face v3

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Module Hierarchy ChartsPrivate Sub DrawFace() picFace.Cls picFace.Circle (2400, 2400), 2000

DrawNose DrawEyes DrawMouthEnd Sub

Private Sub DrawNose() If chkNose.Value = vbChecked Then picFace.Line (2400, 2200)-Step(0, 600) End If

End Sub

Private Sub DrawEyes() If optOpen.Value = True Then picFace.Circle (1600, 1600), 500 picFace.Circle (3200, 1600), 500 Else picFace.Line (1100, 1600)-Step(1000, 0) picFace.Line (2700, 1600)-Step(1000, 0) End If

End Sub

Private Sub DrawMouth() If optHappy.Value = True Then picFace.Circle (2400, 2400), 1200, , 3.4, 6 Else picFace.Circle (2400, 4400), 1200, , 0.6, 2.5 End If

End Sub

Private Sub Form_Load() Me.Show DrawFaceEnd Sub

…

DrawFace

DrawEyes

DrawNose

DrawMouth

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Example: Heart RateOption ExplicitDim HR(0 To 6) As Long

Private Sub Form_Load() HR(0) = 134 HR(1) = 127 HR(2) = 139 HR(3) = 155 HR(4) = 143 HR(5) = 151 HR(6) = 141End Sub

Private Sub btnDraw_Click()Dim i As Long picMain.Cls For i = 0 To 6 picMain.Line -(i * 500, HR(i) * 10) NextEnd Sub

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Tutorial Exercises: Hotel Rooms• Task 1: Get the Hotel Rooms examples versions

1, 2, and 3 (from the lecture) working.• Task 2: Modify your code – to give the result 0 if

the user enters a negative number for either number of rooms or number of nights.

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Tutorial Exercises: Face• Task 1: Get the Face examples versions 3 and 4

(from the lecture) working.• Task 2: Modify your code – use constants to

remove all magic numbers.

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Tutorial Exercises: Stick Man• Task 1: Modify your stick man program (from

previous week), to use procedures (decide which lines of code should be grouped together and what name should be used).

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Tutorial Exercises: Heart Rate• Task 1: Get the Heart Rate program (from the

lecture) working.• Task 2: Modify your program, to use procedures

(decide which lines of code should be grouped together and what name should be used).

• Task 3: Modify your program so that the first vertical line (from the origin 0,0) is not drawn.

• Task 4: Modify your program to draw horizontal lines at the 160 and 120 BPM marks.