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Variable
Memory location whose value can change as the
program is running.
Used to hold temporary information
Used to control the type of data used in calculations
Val returns a Double-type, which is often larger than
necessary
Can store only one piece of data at any time
Data is processed faster
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Data Types
Byte
Long
Boolean
Object
Currency
Single
Date
String
Double
Variant
Integer
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Use the Appropriate Data Type
Integer or Long - Used to store whole numbers
Single, Double, Currency - Used to store numbers with a
decimal fraction
String - Used to store strings
Boolean - Used to store Boolean values (True and False)
Date - Used to store date and time information
Object - Used to store a reference to an object
Byte - Used to store binary data
Variant - Flexible, but not efficient
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Variable Names
Should be meaningful
First three characters should represent the
data type
Remainder of name should represent the
variable’s purpose
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Three-character Ids
Byte
byt
Long
lng
Boolean
bln
Object
obj
Currency
cur
Single
sng
Date/Time
dtm
String
str
Double
dbl
Variant
vnt
Integer
int
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Rules for Naming Variables
Name must begin with a letter
Name can contain only letters, numbers, and
the underscore. No punctuation characters or
spaces are allowed
Name cannot exceeds 255 characters
Name cannot be a reserved word
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Creating (declaring) a Variable
Dim variablename [As datatype]
Public variablename [As datatype]
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Assigning Values to Variables
Assignment statement
variablename = value
Examples:
sngHours = 38.5
curBonus = curSales * .1
strName = “Susan”
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Constants
Literal constant
Symbolic constant
an item of data whose
value cannot change
while the program is
running
a memory location whose
contents cannot be
changed while the
program is running
Examples:
Examples:
conPi
7
conRate
“Janet”
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Scope of a Variable
Indicates which
procedures can use the
variable
Determined by where
the Dim or Public
statement is entered
Can be either global,
form-level, or local
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Local Variables
Created with the Dim statement
The Dim statement is entered in an object’s
event procedure
Only the procedure in which it is declared can
use the variable
Removed from memory when the procedure
ends
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Form-level Variables
Created with the Dim statement
The Dim statement is entered in a form’s
General declarations section
Can be used by any of the procedures in the
form
Removed from memory when the application
ends
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Global Variables
Created with the Public statement
The Public statement is entered in a code
module’s General declarations section
Used in multi-form projects and can be used
by any of the procedures in any of the
project’s forms
Removed from memory when the application
ends
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Option Explicit Statement
Doesn’t allow you to create variables “on the
fly”
Enter in every form’s, and every code
module’s, General declarations section
Use Tools, Options, Environment tab, Require
Variable Declaration to have Visual Basic
include Option Explicit in every new form and
module
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Creating a Symbolic Constant
A memory location whose value cannot
change during run time
Syntax: [Public] Const constname [As
datatype] = expression
Examples:
Const conPi As Single = 3.141593
Public Const conMaxAge as Integer = 65
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Scope of a Symbolic Constant
Indicates which procedures can use the
symbolic constant
Global: Public Const statement in a code
module’s General declarations section
Form-level: Const statement in the form’s
General declarations section
Local: Const statement in an event procedure
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String Concatenation
Ampersand - &
Examples: (Assume strFirstName contains “Mary” and
sngSales contains 1000)
“Hello “ & strFirstName
strFirstName & “ sold $“ & sngSales & “.”
Results:
Hello Mary
Mary sold $1000
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InputBox function
Displays one of Visual Basic’s predefined dialog boxes
Contains a message, along with an OK button, a
Cancel button, and an input area
Syntax: InputBox(prompt, title)
Use sentence capitalization for the prompt, and book
title capitalization for the title
Has limitations: can’t control appearance and allows
user to enter only one piece of data
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Newline Character
Chr(13) & Chr(10) - issues a carriage return
followed by a line feed
vbNewLine - one of Visual Basic’s intrinsic
constant
An intrinsic constant is one that is built into
the Visual Basic language
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Object Browser
Dialog box that provides information about
objects available to your application
The Object Browser lists properties, methods,
events, and intrinsic constants
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Default Command Button
Can be selected by pressing the Enter key even
when the button does not have the focus
Set the button’s Default property to True
Only one command button can be the default
If used, it is typically the first button
If a button’s action is destructive and
irreversible, then it should not be the default
button
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InputBox Function
Has the following limitations:
Can’t control its appearance
Allows the user to enter only one piece of data
Used for RAD (rapid application development]
In the final project, InputBox functions are
typically replaced with professional-looking
dialog boxes
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Multi-form Projects
Only one form, called the startup form, is
automatically loaded and displayed
You must include code to load/display the
other forms in the project
Use the Project menu, <Project Name>
Properties, Startup Object list to specify the
startup form
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Loading and Displaying a Form
Visual Basic has two statements and two
methods that control the loading and
displaying of forms
•Load statement
•Unload statement
•Hide method
•Show method
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Load and Unload Statements
Load statement
brings a form into memory, but does not display
the form on the screen
Syntax: Load object
Unload statement
removes a form from both memory and the screen
Syntax Unload object
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Show and Hide Methods
Show method
displays a form on the screen; loads the form if it
is not already in memory
Syntax: object.Show [style], where style , which is
optional, can be either 0 or 1
Hide method
removes a form from the screen, but leaves it in
memory
Syntax: object.Hide
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Style
0 or omitted means that the form is modeless
Example: MSDN Library window
1 means that the form is modal
Example: Visual Basic’s Open Project dialog box
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Standard Windows Dialog Box
Created from a form
Centered on the screen
Not resizable
Contains only a Close button
Set the form’s BorderStyle property to 3-Fixed
Dialog
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Centering Instructions
formname.Top = (Screen.Height - formname.Height)/2
formname.Left = (Screen.Width - formname.Width)/2
Top, Left, Height, and Width properties are measured
in twips
One twip is 1/1440 of an inch.
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Timer Control
Processes code at regular intervals
Interval property
Measured in milliseconds
A millisecond is 1/1000 of a second
Timer event
Contains the code that will be processed when
each interval has elapsed
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Removing a Coded Control
Remove all of the control’s code before
removing the control
Unassociated code remains in the application
Look in the form’s General declarations
section to verify that the application does not
contain any unassociated code
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Appearance of the Mouse Pointer
Controlled by the object’s MousePointer property
Use either an hourglass or an arrow/hourglass to
indicate that the application is busy
The hourglass indicates that the mouse pointer is
temporarily inactive, whereas the
arrow/hourglass indicates that the mouse pointer
still can be used in the current application
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Debugging Technique
Always enter the Option Explicit statement
in the General declarations of every form and
module
If your application uses the InputBox function,
test your application to see how it handles the
various InputBox responses
When using the Val function, remember that
Visual Basic must be able to interpret the string
expression as a numeric value
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