Introduction to Computing Dr. Nadeem A Khan

Lecture 13

► Properties  Name  Max  Min  Value  Large Change  Small Change etc. Scroll Bar (Horizontal and Vertical)

► Events  Change  Scroll etc. Scroll Bar (Horizontal and Vertical) - (Contd.)

► Read about them in the book Timer, Line, Shape

► Try out various formatting commands in the Format Menu the Format Menu The Format Menu

States of Visual Basic Three states of Visual Basic: ► Design State ► Execution State and and ► Break State

States of Visual Basic (Contd.) ► Break State: Execution interrupted temporarily  Press F5 to resume or choose Run > Continue  Immediate Window is activated  Can edit code, Issue commands in the immediate window, Cannot edit the user-interface

► Useful for debugging ► Tryout commands in the break state like:  Print Label1.Caption  Print ( )/5  Label1.Caption= “Hello World”  Picture1.Print “Hello” The Immediate Window

What is Focus ?

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

► Related Methods  SetFocus ► The statement Text1.SetFocus‘shift focus to Text1 Text Box => Access Key can also be used to get focus Focus (Contd.)

► Names ► Appearance: (Flat look/3-D look etc.) ► BackColor ► ForeColor ► Font ► Caption ► Text ► Width, Height ► Left, Top VB Objects and Properties

► Enabled: True/False  False: ► Cannot accept user input ► Cannot get focus ► Visible: True/False  False: Control is invisible etc. VB Objects and Properties (Contd.)

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 VB Objects and Methods

► Move: For moving and resizing objects e.g:  Control.Move left, top, width, height =>more on Methods in book or use help VB Objects and Methods (Contd.)

Event is a control’s 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 VB Objects and Events

► Click, DblClick:  events related to pressing left mouse button ► KeyPress:  Events related to pressing a key 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 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 VB Objects and Events (Contd.)

 Application does not determine the flow; Events caused by the user determine the flow Event-Driven Programming

Object Oriented Programming?

Built-in Functions ► Take one or more input values ► Return an output value ► Already seen:  Val(..), Str$(..), Asc(..), Chr(..)

Built-in Numeric Functions ► Sqr: calculates square-root and returns the value as double data type e.g: e.g:  Sqr(9) is 3  Sqr(0) is 0  Sqr(2) is  Sqr(30*2+4) is 8

Built-in Numeric Functions ► Int: Greatest integer less than and equal to a number e.g: e.g:  Int(2.7) is 2  Int(3) is 3  Int(-2.7) is -3

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”

Remember Assignment 4 ► It has been posted: See the Website

Refer to: ► Schneider: Section 3.6 ► Brown: Chapter 3(p76-104; p115-p127)