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Visual Basic Fundamental Concepts

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.

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Visual Basic Fundamental Concepts

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  1. Visual Basic Fundamental Concepts

  2. 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.

  3. Toolbox Label control Textbox control Button control Toolbox and Controls

  4. 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.

  5. 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.

  6. Controls and Associated Events

  7. 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

  8. 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

  9. Syntax of Dim and Assignment Statements • Dim • Dim <variable> as <data-type> • Dim avg as double • Dim nmbr as integer • Dim flag as boolean • Assignment • <variable> = <expression> • avg = (nmbr1 + nmbr2) / 2 • flag = false

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

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

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

  13. View StartupForm andSet Properties

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

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

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

  23. Data types and Statement Types

  24. Controls and Associated Events

  25. 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

  26. Average of List of Grades

  27. If statement for Control • If statement performs an action (<statement_list>) if a condition (<condition>) is true. • Syntax : • If <Condition> then • <statement_list> • End if

  28. If statement Example with Else part • Syntax with Else • If <Condition> then • <statement_list1> • Else • <statement_list2> • End if • Example : • If hours > 40 then • overtimeHours = hours – 40 • Else • overtimeHours = 0 • End If

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