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03 – Debugging & Graphics

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Session Aims & Objectives• Aims

– tidy up from last session– introduce you to testing and debugging process– introduce you to graphics

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

– Test program– Identify and correct simple logical and syntax errors– put bitmap (raster) graphics into you applications– draw simple vector graphics

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Example 2-6: Address Book

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Testing & Debugging: Errors• 3 error types :

– syntax: computer unable to understand your instructions (program does not execute), e.g.

• variable not defined (probably most common)

– run-time: program can't execute instruction and exits (future lecture)

• device not available

– logical: program executes but does not not match specification (do what was intended), e.g.

• clicking on button does nothing, when you thought you attached code to it

• clicking on blue button changes colour to red (when it should change to blue)

Music Player

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• Computer – just symbol matching– No intelligence

Example 1: Hello Errors

Sub Command1_Cluck LabelL.Caption = "Hello"End Sub

L instead of 1: causes syntax error (variable not defined)

u instead of i: causes logical error (Command1 button does nothing)

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Exercise 1: Errors

• The following is from exercise 1 (v1),– Spot the errors (you should find 6), and– decide whether they are syntax or logical

Private Sub btnBlue_Cluck() lblResult.BackColor = vbRedEnd Sub

Private Sub btnRed_lick() lblResult.BackColor vbRedEnd Sub

Private Sub lb1Result_DblClick() lblResult.BackColour = vbWhiteEnd Sub

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Verification & Validation

• Verification:– 'Are we building the product right?'– Does software match software requirements

specification?

• Validation:– 'Are we building the right product?'– Does the software requirements specification

meet the user requirements?

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Debugging: Testing

• Functional Decomposition– break it into logical chunks

• Incremental Development– type a bit– test it

• Testing– test all/most combinations

• Regression Testing– repeat all previous tests

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Types of Graphics: Raster

• Raster graphics – made of dots (pixels – picture elements)– suitable for complex, static pictures (e.g. photos)– difficult to change programmatically– loses quality when enlarged

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Types of Graphics: Vector

• Vector graphics – made of objects (lines, circles, etc.)– suitable for simple, dynamic pictures (diagrams)– No loss of quality when enlarged

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Picture Control

• Methods (vector graphics)– Line: draws a straight line between 2 points– Circle: draws a circle– PSet: draws a dot (point)– Cls: clears (screen) drawing area

• Properties– Picture: allows display of bitmap (raster graphic) as

background

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Graphics: Grid System

• the origin (position 0,0) is at top left– in mathematics it is always bottom left

200010000

0

1000

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Example 2: Shapes

• Form and Picture Box control support graphics methods:

0 200010000

1000

picDisplayArea.Line (500, 200)-(1900, 800)picDisplayArea.Line -(2600, 600)picDisplayArea.Line -Step(-600, -400)

picDisplayArea.PSet (1500, 1000)picDisplayArea.Circle (700, 900), 300

Shapes

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Example 3: StickMan

• Enabled property (true or false)

StickMan

200010000

0

1000

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Example 4: Face

Face

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Example 5: Picture Viewer– LoadPicture function:

picDisplay.Picture = LoadPicture("C:\Cat.jpg")– Pattern property (of file list)

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Example 6: Music Player v3

V3

Option Explicit

Private Sub drvMain_Change() dirMain.Path = drvMain.DriveEnd Sub

Private Sub dirMain_Change() filMain.Path = dirMain.PathEnd Sub

Private Sub filMain_Click() mmcMain.Command = "Close" mmcMain.FileName = filMain.Path & "\" & filMain.FileName mmcMain.Command = "Open" pgbMain.Max = mmcMain.Length pgbMain.Value = 0End Sub

Private Sub mmcMain_StatusUpdate() pgbMain.Value = mmcMain.PositionEnd Sub

Private Sub mmcMain_Done(NotifyCode As Integer) filMain.ListIndex = filMain.ListIndex + 1 mmcMain.Command = "Play"End Sub