Scope, Variables, and Parameters in VB
Motivation
We already know the concept of variables and constants in Pseudocode. Let's extend that to VB We've already seen the dim statement, so let's formalize this construct
Built-In Types to VB
Numeric Integer & Long (whole numbers) Single & Double (decimal numbers) String Fixed & variable length Boolean Others Variant Object Currency Date
Choosing Variable Types
Technically, everything could be variant and we could depend upon the VB interpreter to deal with types This is inefficient Rule of thumb (same as Pseudocode) Choose the type which allows you do to what you need to do Choose the "smallest" data type that meets your needs
Variable Naming
Variable identifiers must Begin with an alphabetic character ('a', 'b', 'z') Cannot contain spaces Can't contain special characters (%, &, !, #, @, or $) Must be unique within the scope of their use
Hungarian (Prefix) Notation
Boolean Byte Currency Date Double Integer Long Object Single String Variant bln byt cur dt dbl int lng depends upon object sng str AllthankstoMicrosoftsChief var
ArchitectDr.CharlesSimonyi
Option Explicit
By default, VB can automatically use variables without them having been defined This is bad practice because it lends itself to errors To enforce strict variable declaration before use: option explicit (default settable under Tools | Options | Editor | Require Variable Declaration)
Declaring Variables
Use the dim statement dim VARIABLE_IDENTIFIER as TYPE Examples: dim intAge as Integer dim strName as String dim curSalary as Currency
Variant Rears It's Evil Intent to Rule the World
What are the types of the following variables as declared below? dim intAge, intSSN as Integer
Variable Scope
Similar to Pseudo-code: Visible only within the scope in which it was declared You can Declare variables inside of procedure a Declare variables in the "General Declarations" section of a form/module Declare variables visible to the entire project (public)
Public vs. Private
Within a form module, you can define procedures & variables These can be visible to all procedures within the form module (private) They can also be declared to be visible to all other form modules (public) Public/Private VARIABLE_IDENTIFIER as TYPE
Static vs. Non-static Variables
Normally, a variable declared within a procedure "lives" only as long as that procedure is active If we want persistence between procedure calls, we use the static keyword when defining our variables static VARIABLE_IDENTIFIER as TYPE More on this later
Constants
Declared similarly to variables, but their values don't change Const CONST_IDENTIFIER as TYPE = VALUE Example: Const PI as Double = 3.1415
Event Procedures
We've seen these already!
Private Sub ControlName_EventName (parameters) COMMANDS End Sub Private Sub Form_EventName (parameters) COMMANDS End Sub
General Procedures
These are procedures that you define yourself
They can be Sub (aka P...