Mark Dixon, SoCCE SOFT 136Page 1 05 – Conditional Execution.

Mark Dixon, SoCCE SOFT 136 Page 1

05 – Conditional Execution


Session Aims & Objectives• Aims

– to introduce the main concepts involved in getting the computer to act differently under different circumstances

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

– evaluate conditional expressions, and– implement decision trees in code


Adaptive Behaviour• So far

– every statement always executed in sequence

• Often necessary for software to– change behaviour under different circumstances


Example: Multiplication TestSPECIFICATION

• User Requirements – A primary school teacher wants to test the

multiplication skills of her children.

• Software Requirements– Functional:

–display a multiplication question–allow the user to type a response–check the response and provide feedback

– Non-functionalshould be interesting, colourful, and easy to use


Example: Multiplication Test v1

Option Explicit

Private Sub btnCheck_Click() If txtAns.Text = 15 Then lblMessage.Caption = "Correct, well done!" Me.BackColor = vbYellow Else lblMessage.Caption = "Sorry, 5 times 3 is 15" Me.BackColor = vbRed End IfEnd Sub

lblMessage

btnCheck

txtAns


If Then statements• Use the following syntax:

If condition Then [statementblock]End If

• For example:If txtAge.Text < 21 Then lblResult.BackColor = vbRedEnd If


If Then Else statements• Use the following syntax:

If condition1 Then [statementblock-1][Else [statementblock-2]]End If

• For example:If txtAge.Text Then lblResult.BackColor = vbRedElse lblResult.BackColor = vbBlueEnd If


Conditions & Relational Operators

• Conditions – expression, evaluates to:– true (stored as –1)

– false (stored as 0)

• contain relational operators:= is equal to> is greater than< is less than>= is greater than or equal to<= is less than or equal to<> is not equal to


Examples: Conditions• Using literals:

(34 = 34) (evaluates to true)(34 = 12) (evaluates to false)(34 > 4) (evaluates to true)(18 <=18) (evaluates to true)

• Using controls' properties:picMain.Left = 2300 (picMain.Left = 2300) (true) (picMain.Left = 2309 (false) (picMain.Left <> 189 (true) (picMain.Left > 1900 (true)


Example: Multiplication Test• Problem

– if user enters non-numeric data, then an error occurs


Example: Multiplication Test v2

Option Explicit

Private Sub btnCheck_Click() If txtAns.Text = 15 Then lblMessage.Caption = "Correct, well done!" Me.BackColor = vbYellow Else lblMessage.Caption = "Sorry, 5 times 3 is 15" Me.BackColor = vbRed End IfEnd Sub

Private Sub txtAns_KeyPress(KeyAscii As Integer) If KeyAscii < 48 Or KeyAscii > 57 Then KeyAscii = 0 End IfEnd Sub

code of key thatwas pressed

executed every timekey is pressed

cancels key press


Logical Operators

• And True when both items are True(picMain.Top > 5) AND (picMain.Top < 35) (true)(picMain.Top < 10) AND (picMain.Top > 55) (false)(picMain.Top > 6) AND (picMain.Top < 23) (false)(picMain.Top >=6) AND (picMain.Top <= 23) (true)

• Or True when either item is True(picMain.Top = 23) OR (picMain.Top = 11) (true)(picMain.Top < 10) OR (picMain.Top > 55) (false)

• Not True when item is FalseNot (picMain.Top = 23) (false)

Use to join conditions (assume picMain.Top is 23):


Questions: Conditions• What is the result of (picMain.Left is 5589):

(picMain.Left > 4400)

• What is the result of (txtAge.Text is 19, txtSalary.Text is 10787):

(txtAge.Text < 21) AND (txtSalary.Text < 10787)

• Write an expression to:

check if picMain.height is larger than 167.78

• Write an expression to:

check if picMain.Top is larger than picBall.Top

true

false

(picMain.Height > 167.78)

(picMain.Top > picBall.Top)


Example: Student Loan v1

Option Explicit

Private Sub btnCalc_Click() lblResult.Caption = (txtIncome.Text - 15000) * 0.09End Sub

SLC


Example: Student Loan v2

Option Explicit

Private Sub btnCalc_Click() If txtIncome.Text > 15000 Then lblResult.Caption = "£" & (txtIncome.Text - 15000) * 0.09 Else lblResult.Caption = "You pay nothing (£0.00)!" End IfEnd Sub


Example: BallChar v3

Option Explicit

Private Sub tmrLeft_Timer() ' You need to work this out!End Sub

Private Sub tmrRight_Timer() picBallChar.Left = picBallChar.Left + 100 If picBallChar.Left >= Me.ScaleWidth Then tmrRight.Enabled = False tmrLeft.Enabled = True End IfEnd Sub

BallChar v3

tmrLeft

picBallChar

tmrRight


• Check Box - give user on/off, yes/no choice– Value:

• 1 (vbChecked) if selected• 0 (vbUnchecked) if not selected

• Option Box - Used as a group to give usermultiple options (only 1 item selected at a time)– Value:

• -1 (True) if selected• 0 (False) if not selected

• Can place option boxes in Frame control:– groups option boxes

Selection/Decision controls


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


Decision Trees• Natural language

– ambiguous & difficult to follow

• Decision trees– express same information clearly

Delivery Fee

<= 5 miles

> 5 miles>= £10

< £10

Free

£1.50

£3.00


Example: Pizza DeliveryOption Explicit

Private Sub btnCalc_Click() If txtDist.Text <= 5 Then lblDel.Caption = 0 Else If txtCost.Text >= 10 Then lblDel.Caption = 1.5 Else lblDel.Caption = 3 End If End IfEnd Sub Delivery

lblDelbtnCalc

txtDist txtCost


Tutorial Exercises: Multiply• LEARNING OBJECTIVE:

use if statement to perform conditional execution

• Task 1: Get the Multiply v1 and v2 examples (from the lecture) working.

• Task 2: Modify your program so that the keyboard cursor is put in the text box automaticallyHINT: use the SetFocus method

• Task 3: Modify your program so that the text box is disabled after the answer is checked

• Task 4: Modify your program so that a happy/sad face is drawn depending on whether the answer was correct.

• Task 5: Modify your program so that it makes a suitable sound when the user gets the answer right/wrong.Sound files are in the resources section of the web-site


Tutorial Exercises: Student Loan• LEARNING OBJECTIVE:


• Task 1: Get the Student Loan v1 and v2 examples (from the lecture) working.

• Task 2: Modify your program so that it calculates and displays monthly income and repayment amounts (as well an annual).


Tutorial Exercises: BallChar• LEARNING OBJECTIVE:


• Task 1: Get the BallChar example (from the lecture) working.• Task 2: Modify your program so that the Ball Character blinks

when it is clicked• Task 3: Modify your program to play a sound when the ball

character is clicked


Tutorial Exercises: Face• LEARNING OBJECTIVE:

use if statement with selection controls

• Task 1: Get the Face example (from the lecture) working.• Task 2: Modify your program so that the face is coloured in

(e.g. eyes white, face pink) – be creativeHINT: use the FillColour and FillStyle properties (described in previous lecture)

• Task 3: Modify your program to use sound (happy sound for a happy face, etc)


Tutorial Exercises: Pizza Delivery• LEARNING OBJECTIVE:

use nested if statements (one inside another)

• Task 1: Get the Pizza Delivery examples (from the lecture) working.

• Task 2: Modify your program to calculate the total cost of the order, as well as the delivery cost.


Tutorial Exercises: Music Player• LEARNING OBJECTIVE:

use if statements

• Task 1: Modify your Music Player (from previous week) to automatically move to the first track (file) in the current folder, when the last track finishes playing.Hint: You will need to use the File List Box’s ListCount property.

Mark Dixon, SoCCE SOFT 136Page 1 05 – Conditional Execution.

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true end

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vbred end

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