Scope of Variables and Constants A Variable or Constant may exist and be Visible for an entire project, for only one form, or for only one procedure Therefore, the visibility of a variable or constant is referred to as its Scope Visibility means that

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Scope of Variables and ConstantsA Variable or
Constant may exist and be Visible for an entire
project, for only one form, or for only one
procedureTherefore, the visibility of a
variable or constant is referred to as its
ScopeVisibility means that can this variable
be seen in this locationThe scope of a
variable or constant is said to be Global, Module
(Form) Level, or Local
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Module Level variables or constants are
accessible from all procedures of a FormA Local
variable or constant may be used only within the
procedure in which it is declaredThe Scope of
a Variable declared with a DIM statement is
determined by where the declaration statement is
madeThe Lifetime of a Variable is the period of
time that the variable existsThe Lifetime of a
Local variable is normally one execution of the
procedureThe Lifetime of a Module Level variable
is the entire time the Form is Loaded (generally
the lifetime of the entire project)
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Local Declarations

• Any variable you declare inside a procedure
• The lifetime of the variable is one execution of
  the procedure
• Each time you execute (e.g. click on a command
  button) a procedure, the local DIM statements are
  executed.
• Each variable is created as a fresh new one
  with an initial value of 0 for numeric datatypes
  or for string
• When the procedure finishes, its variables
  disappear, their memory locations are released

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Local Declarations
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Module-Level Declarations

• When you need to use a variable or constant in
  more than one procedure of a form
• Declare at module-level
• General Declarations

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Module-Level Declarations
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Global Variables

• Though you can declare global variables anywhere,
  convention dictates that public variables be
  placed only in the standard code module.
• Examples of global and module level declarations
  in a SCM
• Public gcurTotalSalary as Currency 'global
  variable
• Public Const gcurTAX_RATE as Single .082
  'global constant
• Dim mcurMySalary as Currecy 'module-only variable
• If a procedure were to contain a variable
  declared locally whose name is the same as a
  global variable (a violation of unwritten
  convention for variable naming), then the local
  variable takes precedence. A local variable, when
  in scope, always preempts use of a global
  variable.
• The Private statement is rarely used, because
  that is the default (for Dim)

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Static Variables

• Static variables are local to a procedure but
  retain their value for the life of a project.
  They are often used inside a procedure that
  counts things and must maintain that count.
  Static variables are initialized once only.
  Thereafter they are not initialized during the
  project
• Private Sub Something()
• Static intCount as Integer 'initialized
  to 0 once
• intCount intCount 1 'remembered across
  invocations
• End Sub

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Standard Code Modules

• Public procedures arevisible to all forms
• Public variables are visible to all forms
• SCM has the extension .BAS
• Create SCM Project, Add Module
• DIM variables in the code module are visible to
  all procedures in the module, but not to
  procedures in the form modules.
• SCM modules do not have any event procedures
  because SCM has no events to which it can react.
  The SCM only has code and procedures.

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Identifiers

• When you use variables and constants, it is
  important that you know their scope. Good
  programming practice to include scope information
  in naming conventions
• Use m as a prefix to identify module-level
  declarations
• Use g to identify variables with global scope

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Multi-Form ProjectsWorking with more than one
form in a projectThe first form that VB
displays is called the STARTUP FORMTo add
another form Project Menu/Add Form or select the
icon from the shortcut toolbarThis form will be
added to the project, and cam be viewed from the
Project Explorer Window
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Each form is a separate entity, and the code
exists and is related only to the specific
formTo move between each formFORMNAME.SHOWFO
RMNAME.HIDEForm style can be 1 (modal) or the
default value 0 (nonmodal)
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Variables Constants in Multi-form Projects

• Scope of variables
• Local available inside a procedure
• Static inside procedure, but remembered
• Module level available anywhere in a form
• Global available across forms--anywhere
• Global variables declared with Public
• Variable prefix naming conventions m for module,
  g for global
• Scope a variable as narrowly as possible

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Referring to Other Forms Objects

• You can refer to txtName in another form called
  frmSummary this way
• frmSummary!txtName
• or frmSummary!txtName.Font.Name ...
• This implies that control names are unique within
  a form but need not be unique across forms.

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An About Box

• Acts like a Windows HelpAbout box
• Often displays information about the programmers,
  designers, and so on
• An about box is simply a modal form with an OK
  button and label boxes displaying information
• You can use VBs About Dialog template

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A Splash Screen

• Splash screen displays while product loads
• Create Project, Add Form, then select Splash
  Screen
• Splash screen loads first instead of main form
• Place splash screen load statement in Sub Main
  procedure in Standard Code Module