outline

Variable Description

• A container for information (data)
• A name that refers to a chunk of computer memory
• Variables have value
• Can be used in statements rather than a value
• Value can change

Principal Uses

• Storing information gotten from the user, environment or another source
• Works with information stored in object properties
• Can manipulate information (info garage)

Type of Variables

• Computer stores different types of information in different ways
• Examples:
  Text - fixed or dynamic length
  Integers - integers or long integers
  Real numbers - single and double precision
  Currency - 8 digits plus four decimal places
  Variant - computer takes its best guess (risky)

Variable Declaration Modes

• Implicit - simply by using the variable you declare its existence
• This is used by older forms of Visual Basic
• Used type declaration characters ($ % & #, etc.)
• There is no way to check for spelling of variable names - common errors

Explicit Declaration

• Each variable is declared in a DIM statement, using a variable name and the type
• Example Syntax:
  - Dim UserName as String
• Variable should be declared before the code using it in the appropriate code area
• Can also be set by typing OPTION EXPLICIT in the General area of the form

Advantages of using variables

• Your code is easier to read
• Misspelling variable names is caught by the complier
• Makes it easier to set the scope
• More professional

Scope

• There are different levels where you define variables
  1. Procedure
  2. Form or general declarations
  3. Project level (global)

Description

• Variables can be accessed only in specific parts of the program
• Prevents errors especially in large programs
• Allows for compartmentalization of the program
• Variables are only available to those parts of the program that need it

Law Enforcement

• Scope can be compared to different types of law enforcement:
  local = same as local police
  general or form = county sheriff
  global = state police

General (form) Level Variables

• Are declared in the general area of the form
• Are available to all objects and code windows attached to the form
• The value of the variable is accessible to any code in the form
• NOT the same as a global variable

Object Level Variables

• Are declared in the code window of the specific object
• Exists only when that code is running
• If the same variable name is used in a different code window, they are DIFFERENT variables
• Also called local variables and are preferred when possible

Which should you use?

• If only one object will use the information stored in the variable, make it Object Level
• If more that one object needs it, make it Form Level…more later

Type Conversion Functions

• This allows you to convert from one data type to another
• Val - grabs a numeric value from a string
• Str$ (Str) converts a numeric value to a string
• Is frequently used to convert from variant to a more specific type

Simple Dialog Boxes

• Message Box (MsgBox) is a easy way to send a short message to a user
• Syntax: MsgBox ("String value to send")
• Example: MsgBox ("Hello World")
• Or: Dim Message as String
    Message = "Hello World"
     MsgBox (Message)

Inputbox

• These are easy ways to get quick input from the user
• Syntax: VariableName = Inputbox(String value representing questions)
• Example: Dim UserName as String
      UserName = Inputbox ("What is your name?")
      or , Dim Answer as Integer
      Answer = Inputbox ("What is 5 + 3 ?")

If - Then - EndIf

• Allows for simple evaluations
• Syntax: IF expression THEN command
• Example: If Name = "Wally" then MsgBox ("You're a Nerd")
  If Answer <> 12 then MsgBox ("Sorry, 5 + 7 = 12")

Block for of IF Else EndIF

• IF expression THEN
     code
  ELSE
     more code
  END IF

Example:

• IF Ans4 = Total THEN
      MsgBox ("Very Nice!")
  ELSE
      MsgBox ("Too Bad !")
  END IF