Introduction to Visual Basic

Visual Beginners All-Purpose Symbolic Instruction Code

Visual Basic

• is a tool that allows you to develop Windows (Graphic User Interface - GUI) applications.

• is event-driven, meaning code remains idle until called upon to respond to some event.

Steps in Developing Application

1. Draw the user interface2. Assign properties to controls3. Attach code to controls

Draw the User Interface

Visual Basic operates in three modes.• Design mode - used to build application• Run mode - used to run the application• Break mode - application halted and debugger

is available

Getting Started

7 Windows

1. Main Window2. Form Window3. Toolbox4. Properties Window 5. Form Layout Window6. Project Window7. Code Editor Window

Main Window

• consists of the title bar, menu bar, and toolbar.

Form Window

• is central to developing Visual Basic applications. It is where you draw your application.

Toolbox• is the

selection menu for controls used in your application.

Properties Window

• is used to establish initial property values for objects.

Form Layout Window

• shows where (upon program execution) your form will be displayed relative to your monitor’s screen.

Project Window

• displays a list of all forms and modules making up your application.

Code Editor Window

• Contains the actual Basic coding.

Assign Properties to Controls

• Naming Convention of ControlsObject Prefix Example

Form frm frmHello

Command Button cmd, btn cmdExit, btnStart

Label lbl lblStart, lblEnd

TextBox txt txtTime, txtName

Menu mnu mnuExit, mnuSave

Check box chk chkChoice

Attach Code to Controls

• Code in a Visual Basic application is divided into smaller blocks called procedures.

• Event procedure syntax:

object name_event ()Ex. Command1_Click ()

Private Sub object name_event ()

End Sub _______________________________________

Private Sub Command1_Click ()

End Sub

Private Sub Command1_Click ()

object name.property = valueEnd Sub_______________________________________Private Sub Command1_Click ()

Text1.Text = "Hello, world!"End Sub

Variables

Rules used in naming variables:• No more than 40 characters.• They may include letters, numbers, and

underscore (_).• The first character must be a letter.• You cannot use a reserved word.

Data Types

Variable Declaration1. Default (variant)2. Implicit

Amount% = 3003. Explicit

four levels of scope• Procedure level• Procedure level, static• Form and module level• Global level

• Procedure levelDim Variable name as Data type

Ex. Dim Myint as integer• Procedure level, static

Static Variable name as Data typeEx. Dim Myint as integer

• Form and module levelDim Variable name as Data type

Ex. Dim Myint as integer• Global level

Global Variable name as Data typeEx. Dim Myint as integer

• Procedure Routine1 has access to __, __, and __(…..)

• Procedure Routine2 has access to __, __, and __(…..)

• Procedure Routine3 has access to __, __, and __(…..)

• Procedure Routine1 has access to X, Y, and A (loses value upon termination)

• Procedure Routine2 has access to X, Y, and B (retains value)

• Procedure Routine3 has access to X, Z, and C (loses value)