Introduction to Computing

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Introduction to Computing

• Dr. Nadeem A Khan

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Lecture 13
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Scroll Bar (Horizontal and Vertical)

• Properties
• Name
• Max
• Min
• Value
• Large Change
• Small Change
• etc.

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Scroll Bar (Horizontal and Vertical)
- (Contd.)

• Events
• Change
• Scroll
• etc.

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Timer, Line, Shape

• Read about them in the book

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The Format Menu

• Try out various formatting commands in
• the Format Menu

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States of Visual Basic

• Three states of Visual Basic
• Design State
• Execution State
• and
• Break State

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States of Visual Basic (Contd.)

• Break State Execution interrupted temporarily
• Press F5 to resume or choose Run gt Continue
• Immediate Window is activated
• Can edit code, Issue commands in the immediate
  window, Cannot edit the user-interface

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The Immediate Window

• Useful for debugging
• Tryout commands in the break state like
• Print Label1.Caption
• Print (1234)/5
• Label1.Caption Hello World
• Picture1.Print Hello

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What is Focus ?
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Focus

• The ability of a control to receive user input
• Related Events
• GotFocus
• LostFocus
• Related Properties
• TabIndex
• TabStop

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Focus (Contd.)

• Related Methods
• SetFocus
• The statement
• Text1.SetFocus shift focus to Text1 Text Box
• gt Access Key can also be used to get focus

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VB Objects and Properties

• Names
• Appearance (Flat look/3-D look etc.)
• BackColor
• ForeColor
• Font
• Caption
• Text
• Width, Height
• Left, Top

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VB Objects and Properties (Contd.)

• Enabled True/False
• False
• Cannot accept user input
• Cannot get focus
• Visible True/False
• False Control is invisible
• etc.

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VB Objects and Methods

• Methods are actions that objects can carry out
• Print
• e.g
• Picture1.Print
• Printer.Print
• Form1.Print
• Cls Contents are discarded
• e.g
• Picture1.Cls to clear the text in the picture
  box
• Form1.Cls to clear the text on the form

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VB Objects and Methods (Contd.)

• Move For moving and resizing objects
• e.g
• Control.Move left, top, width, height
• gtmore on Methods in book or use help

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VB Objects and Events

• Event is a controls response to an external
  action
• Change
• e.g
• VScroll1_Change (Value property of the Scroll Bar
  is changed)
• Text1_Change (each time a new character is typed
  in or deleted in the Text Box)
• Check1_Change (each time the user changes the
  status of the Check Box by clicking it

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VB Objects and Events (Contd.)

• Click, DblClick
• events related to pressing left mouse button
• KeyPress
• Events related to pressing a key

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VB Objects and Events (Contd.)

• More Events
• related to Mouse
• MouseDown, MouseUp, MouseMove etc.
• related to keyboard
• KeyDown, Keyup etc.
• more on Events in book or use help

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VB Objects and Events (Contd.)

• Event procedures implement the user-response
• Sub Label1_DblClick( )
• Rem An event procedure with no arguments
• .
• End Sub
• Sub Text1_KeyPress(KeyAscii As Integer)
• Rem An event procedure with an argument KeyAscii
• ..
• End Sub

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Event-Driven Programming

• Application does not determine the flow
• Events caused by the user determine the flow

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Object Oriented Programming?
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Built-in Functions

• Take one or more input values
• Return an output value
• Already seen
• Val(..), Str(..), Asc(..), Chr(..)

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Built-in Numeric Functions

• Sqr calculates square-root and returns the value
  as double data type
• e.g
• Sqr(9) is 3
• Sqr(0) is 0
• Sqr(2) is 1.414214
• Sqr(3024) is 8

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Built-in Numeric Functions

• Int Greatest integer less than and equal to a
  number
• e.g
• Int(2.7) is 2
• Int(3) is 3
• Int(-2.7) is -3

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Built-in String Functions

• Left, Mid, Right, UCase, Trim
• Left(fanatic, 3) is fan Right(fanatic,
  3) is tic
• Left(12/15/93,2) is 12 Right(12/15/93,
  2) is 93
• Mid(fanatic, 5,1) is t Mid(12/15/93,4,
  2) is 15
• Ucase(Disk) is DISK Ucase(12two) is
  12TWO
• Trim( 1 2 ) is 1 2 Trim(-12 ) is -12

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Remember Assignment 4

• It has been posted See the Website

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Refer to

• Schneider Section 3.6
• Brown Chapter 3(p76-104 p115-p127)