Visual Basic Fundamental Concepts

Integrated Development Enviroment Generates startup form for new project on which to place controls. Features toolbox from which controls can be selected & placed on form. Features intellisense which prompts for completion of statement or object reference. Provides immediate syntax checking. Provides online debugging, displaying intermediate values. Provides HELP feature.

Toolbox and Controls Label control Textbox control Button control Toolbox

Basic Controls Label : Displays information through its Text property. Textbox : Information Entry, Display, and Transfer through its Text Property. Use name of textbox to access information or respond to Gotfocus event. Button : Information Display through its Text Property. Use name of button to respond with subroutine to its Click event.

Event Driven Programming Before event driven programs, typical applications were executed by the computer under control of the application. With event driven programs, the operating system detects user interactions (mouse click, tab key, etc.), passes them to the application, and a control responds by running a subprogram.

Controls and Associated Events ControlEvent FormLoad event occurs when form is loaded into computer memory ButtonClick event occurs when user clicks button with mouse TextboxLostfocus event occurs when user tabs out of box

Click event for Avg button Private Sub cmdAvg_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdAvg.Click 'Compute average and store in text property of tbAvg control tbAvg.Text = (CInt(tbNum1.Text) + CInt(tbNum2.Text)) / 2 tbNum1.Select() tbNum1.SelectionStart = 0 tbNum1.SelectionLength = tbNum1.Text.Length tbNum2.Clear() lblStep1.Visible = True lblStep2.Visible = False End Sub

Variables and Data Types Variables are assigned values from a data type VB data types include String, Integer, Double, and Boolean A Dim statement is used to declare a variable and the data type from which its values are assigned

Syntax of Dim and Assignment Statements Dim – Dim as Dim avg as double Dim nmbr as integer Dim flag as boolean Assignment – = avg = (nmbr1 + nmbr2) / 2 flag = false

Variables and Assignment Statements Dim message As String ‘declares string variable 'Assign string constant to messages 1 and 2 ‘ Assignment statement : = message = "Enter numbers to be “ & _ “averaged in 1st and 2nd textboxes“ lblStep1.Text = message message = "Click Average button" lblStep2.Text = message

Creating a New Project Open Visual Studio 2005 Click Project after Create:

Choosing Project Language, Template, and Project Name Select Visual Basic – Windows Windows Application Enter Project Name (Lab1 in example) Click OK

View Startup Form and Set Properties

Problem Analysis & Application Development Analyze Problem – Example : Find averages of pairs of numbers, number1 and number2 – Input : number1, number2 – Process : average = (number1 + number2) / 2 – Output : average

Project Implementation & Software Development Design Solution – Choose forms and controls Select label – textbox pairs for – Input : number1 and number2 and – Output : average Select buttons to launch processes – Average Write code to implement process Gets number1 and number2 values Computes average = (number1 + number2) /2 Displays average

Select Label Control from Toolbox Click on Form to position Label – drag if desired. Click on Textbox Control from Toolbox Click on Form to position Textbox to right of Label

Name textbox tbNumber1 Holding shift key down, select label and textbox together Copy with Ctrl-C Paste with Ctrl-V (for Number2 entry. Select button Control and position below label – textbox pair Paste again below button for output. Set text properties of labels and the button Name textbox and button controls Write code for button click event – double click on button to generate subroutine shell Label – textbox pair Copy with Ctrl-C

Controls after selection Now set text properties of labels and the button Name textbox and button controls Write code for button click event – double click on button to generate subroutine shell

Controls after setting text properties of labels and the button Name textbox and button controls Name of textbox for output Write code for button click even by double clicking button Button code should Compute & display average Clear input boxes and select first box

Write code for button click event by double clicking button Button code performs following: Computes average Displays average Clears input boxes and selects first box

Test Program in debugger by switching back to design view Click debugger button

Copy Screen to Copy Buffer by doing a Print Screen Paste onto a Word Document Type your name & turn in.

Data types and Statement Types Data Type Values Statement Type Syntax Integer 3, 211, -42,. Declaration Dim as Double 3.17, Assignment = String “Hello”, “Bob” Selection If then End if Boolean True, False Repetition For = to Next

Controls and Associated Events ControlEvent FormLoad event occurs when form is loaded into computer memory ButtonClick event occurs when user clicks button with mouse TextboxLostfocus event occurs when user tabs out of box ListboxSelectedIndexChanged occurs when user clicks a list item with mouse

Problem Analysis & Application Development Analyze Problem – Example : Find average of list of numbers incrementally by – Keeping track of number of numbers – Keeping track of sum of numbers – Computing average after each number – Displaying numbers in a listbox

Average of List of Grades

If statement for Control If statement performs an action ( ) if a condition ( ) is true. Syntax : – If then – End if

If statement Example with Else part Syntax with Else – If then – Else – End if Example : – If hours > 40 then overtimeHours = hours – 40 – Else overtimeHours = 0 – End If