Introduction to Computing

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Introduction to Computing

• Dr. Nadeem A Khan

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Lecture 7
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Announcement

• New TAs
• Harris Mukarram
• Mubashir Amjad Hunain
• Visit the Website for their office hours

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How to make our user-interface do something?
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Visual Basic Events

• Event Action taken by the user e.g.
• Clicking a Control
• Double Clicking a Control
• Getting Focus
• Losing Focus
• etc. etc.

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Visual Basic Events (Contd.)

• Naming of Events
• Clicking a Command Button 1
• Command1_Click
• Double Clicking a Picture Box 2
• Picture2_DblClick
• Text box 1 gets Focus
• Text1_GotFocus
• Text box 1 loses Focus
• Text1_LostFocus

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Visual Basic Events (Contd.)

• Names of events
• gt objectName_event
• Events are pre-defined

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Event Procedure

• Event Procedure block of code to be executed
  when an event occurs
• General form
• Sub objectName_event()
• statements
• End Sub

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Event Procedure (Contd.)

• E.g
• Sub Command1_Click()
• statements
• End Sub
• Sub Text1_GotFocus()
• statements
• End Sub

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Statements?
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VB Statements

• Statements to change the properties of an object
• the general form
• Let objectName.property setting

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Statements (Contd.)

• Let objectName.property setting
• E.g
• Let Text1.FontSize 12
• Let Text1.FontBold TRUE
• Let Text1.Text

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Event Procedure (Contd.)

• Event procedure general form
• Sub objectName_event()
• statements
• End Sub
• Example
• Sub Command1_Click()
• Let Text1.text
• Let Text2.textHello
• End Sub

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Viewing Code
Object Box
Procedures List Box
Margin Indicator Bar
Split Bar
Procedure View
Full Module View
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Methods

• Another category of statements based on methods

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Methods (Contd.)

• E.g
• Picture1.Cls
• Clears Picture1 Picture Box
• Picture1.Print 3
• Prints 3 in the Picture1 Picture Box

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Methods (Contd.)

• General form of these statements
• gt objectName.Method parameters
• (if any)

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The Print Method

• Picture1.Print m ?
• Picture1.Print m ?
• Picture1.Print m n r ?
• m, n, r are numbers e.g. 3, 5.2

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Numbers

• Numeric Constants
• 2, 5.6, 9, 10.005
• Arithmetic Operations
• Addition (23)
• Subtraction (2-3)
• Multiplication (23)
• Division (2/3)
• Exponentiation (23)

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Numbers (Contd.)

• Numeric Expressions
• e.g.
• (23)/5
• (52) (2- 10/2)
• 2.52-3214/7

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Numbers (Contd.)

• How will this be calculated?
• 210/5
• 52 2- 1/10
• 46-325/10
• 325

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Numbers (Contd.)

• Operator Precedence
• 1.
• 2.- operator (indicating a negative value)
• 3. and / operator
• 4. and - operator

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Numbers (Contd.)

• Use parenthesis ( ) to keep intentions clear
• (22)2 ?
• 222 ?
• (5 (52))/(21) ?

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Strings

• E.g
• hello
• 9/17/95
• 23

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What will be printed?

• Picture1.Print 232
• Picture1.Print hello
• Picture1.Print 232

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Todays Lecture was based on

• David Schneider
• Chapter 3 Section 3.2

• Scott Warner
• Chapter 2 Section 2.1(p48-p50)
• Chpater5 Section 5.2