Introduction to Visual Basic

1
Introduction to Visual Basic
2
Objectives

• Variables
• Operations
• Conditional Structure
• Loop
• Objects

3
Variables Examples

• Variables are named locations in memory that are
  reserved for the duration of the program.
• when the program terminates, so do all the
  variables.
• Example
• Dim Price As Integer
• Price 150

4
Data Types
5
Examples

• Dim MyName As String
• MyName John
• Dim MyName As String John

6
Arithmetic Operations

• Addition
• - Subtraction
• Multiplication
• / Division

7
Logical Operators
8
Logical Operators
9
Conditions

• If Then
• If grpInfo 1 Then
• MsgBox Group is 1
• End If
• If ThenElse
• If grpInfo 1 Then
• MsgBox Group is 1
• Else
• MsgBox Select another form
• End If

10
Example

• If cond1 Then
• If cond2 Then
• action(s)
• End If
• End If

• If cond1 And cond2 Then
• action(s)
• End If

This is easier to understand
A confusing If Block
11
The Select Case Block

• Similar to If statement
• Used instead of nested If statement
• An action to be selected from a list of
  alternatives
• Avoids confusion of deeply nested If blocks

12
Select Case Block (Syntax)

• Select Case selector
• Case value-list-1
• action1
• Case value-list-2
• action2
• ..
• Case Else
• action of last resort
• End Select

13
Select Case Block

• Each value-list contains one or more of the
  following types of items separated by a comma
• a constant
• a variable
• an expression

14
Example of Select Case

• Select Case letterGrade
• Case A, B
• M.text Good Work
• Case C
• M.text Average Work
• Case Else
• M.text Poor Work
• End Select

15
The Do While . Loop

• Do While condition is true
• statement(s)
• Loop

16
Flowchart for a Do While Loop
Is the condition true
No
Yes
Execute statements within the loop
Execute statements that follow the loop
17
The Do While . Loop

• Is executed as long as the condition is True.
• If condition is False then the next statement
  after the Loop is executed.

18
Object-oriented Programming

• Objects
• An object is a self-contained entity that is
  characterized by a recognizable set of
  characteristics and behavior.
• Objects should have properties and methods

19
Class and Object

• Class is a blueprint for which objects are
  created
• An object is an instance of a class

20
Properties

• Properties are characteristics of an object that
  determine the object
• Examples
• People
• Window
• Form
• DoCmd

21
Method

• Methods are actions that objects can take
• Example
• Dim MyString As String This is a test string
  
• MyString MyString.Trim() This is a test
  string
• MyString MyString.Substring(0, 4) This
• MyString MyString.ToUpper() THIS
• Dim Length As Integer MyString.Length 4

22
Create an Object

• Create an instance of a class, or the object is
  instantiated
• Syntax
• Dim objName As New className
• Example
• Dim objWord As New Word.Application
• Dim rsContacts As New ADODB.Recordset