Variables

1
Variables

• Data Types (see page 88)
• Date - 8 bytes
• Integer 2 bytes -32,768 to 32,767
• Long Integer -2,147,483,648 to 2,147,483,647
• Single (like a float)
• Double ( more precision than a single)
• string 1 byte per character (TEXT)

2
Variables

• Naming Variables
• begin with letter
• max 255 characters
• be unique
• no reserved words
• not have a space, an embedded period or dash
• Declaring Variables
• PrivatePublicDIMStatic varname as datatype

3
Variables

• Private - can be used only in the procedure or
  form on which it was declared
• Public - Used by multiple modules
• Dim - Used in Procedures
• Static - Used in Procedures
• Implicit Declaration - using a variable before it
  is declared
• Explicit Declaration - Declaring a variable
  before you use it.
• Option Explicit (Tools, Options Editor Tab -
  Require variable declarations) in general
  declarations.

4
Variables

• Option Explicit
• If used, the Option Explicit statement must
  appear in a module before any procedures
• When Option Explicit appears in a module, you
  must explicitly declare all variables using the
  Dim, Private, Public, ReDim, or Static
  statements. If you attempt to use an undeclared
  variable name, an error occurs at compile time.

5
Variables

• Option Explicit
• If you don't use the Option Explicit statement,
  all undeclared variables are of Variant type
  unless the default type is otherwise specified
  with a Deftype statement.

6
Variables

• Naming Conventions
• Variable names begin with a 4 character prefix
• first letter (denotes scope)
• m - module level (can be referenced by all
  procedures in a module)
• p - only referenced by a single procedure
• g - global (all modules )
• three characters denote type (see pg 88)
• int - integer, lng - long integer, sng - single,
  dbl -double

7
Variables

• Naming Conventions
• Examples (see pg 92)
• Private msngInterestRate as Single
• Private mintYearTerm as Integer
• Dim psngTax as Single
• Scope and Lifetime of Variables
• Scope - where can the variable be referenced
  (where is it available)
• Lifetime - persistence (how long will it last)

8
Scope and Lifetime of Variables

• Declare variables within event procedures with
  Dim or Static.
• The scope of both are within the procedure only.
  The variable can not be referenced outside the
  procedure.
• The lifetime of Dim is as long as the procedure
  is executed. Once it is complete the value is no
  longer known. It will be re-initialized if the
  procedure is executed again.
• The lifetime of Static is for the length of the
  program.

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Scope and Lifetime of Variables

• Declare form variables or code variables with
  Public or Private
• The scope of Private form variable is that all
  procedures on that form recognize it, but its
  scope is limited to that form only.
• The scope of Public form variable is that any
  form will recognize it.
• The lifetime of Private and Public form variables
  are for the lifetime of the application.

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Examples of Scope and Lifetime of Variables

• Private sub cmdOne_Click()Dim pintA as
  integerDim pintB as integerpintA 2
  pintAPrint pintA, pintBEnd SubPrivate sub
  cmdTwo_Click()Static pintA as integerDim pintB
  as integerpintA 1 pintApintB 5Print
  pintA, pintBEnd Sub

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Examples of Scope and Lifetime of Variables

• Example Continued
• Click on cmdOne will print 2 0Click on
  cmdOne will print 2 0Click on cmdTwo
  will print 1 5Click on cmdTwo will
  print 2 5click on cmdOne will print
  2 0

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Scope and Lifetime of Variables

• If a variable is needed by only one event
  procedure then declare it within that procedure
  using Static or Dim depending on the lifetime of
  that variable.
• If a variable is needed by more than one event
  procedure on a form then declare it as a module
  level with Public or Private.

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Numeric Operations

• Order of operations
• 1. ( )
• 2. raise to a power (23 8)
• 3. / Multiplication and division
• \ Mod integer division integer remainder
• 4. - Addition and Subtraction

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Numeric Operations

• Examples
• 232 4 (5 -2) 232 4 (3) 2 6 4
  3 2 72 74

15
Type Conversion Functions

• If Possible
• Val(string) - converts the string to a number
• Cint(string)- converts the string to an integer
• Clng(string)- converts string to long integer
• CSng(string) - converts string to single
• Examples
• pintres Val(123a456) gt 123
• pintres Cint(123a456) gt error

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Formatting Numeric Values

• Named Formats
• Fixed - two decimal places
• currency - leading and two decimal places
• percent - information as a percentage to 2
  decimal followed by a sign
• (see others in help)
• Design your own with special symbols

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Formatting Numeric Values

• Design your own with special symbols
• 0 - digit placeholder prints tailing or leading
  zeroes
• - digit placeholder, never prints trailing or
  leading zeroes
• . - decimal placeholder
• , separates numbers into thousdands, millions
• - ( ) space - characters are displayed
  exactly as typed

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Formatting Numeric Values

• Examples
• txtoutBox.text format(1234.5, currency)gt
  1,234.50
• txtoutBox.text format(1234.5, .)gt
  1234.5
• txtoutBox.text format(1234.5, 000000.00)gt
  001234.50

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Future Value Function

• Computes the future value of an investment
• FV(rate,periods,payment,presvalue,type
• rate - monthly interest rate
• periods - number of time periods in months
• payment - monthly payment or 0 if fixed amount
• optional (current value for a fixed amount (-))
• optional type (0 or 1 payments made at the
  beginning or end of a period)
• see page 100 for examples

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Miscellaneous Topics

• Setting the focus to a textbox or command button
  by calling the setfocus method.
• txtOne.setfocuscmdone.setfocus
• Clearing text from a text box
• txtOne.text txtOne.text vbNullString
• Unloading a form removes the form from memory
• Visible property (appears on the form at run time)

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Miscellaneous Topics

• Visible property (appears on the form at run time
  if set to true)
• Enabled property (will an object respond to
  events) ture or false