Standard Modules

We will now move into more complex programming techniques.

A Standard Module is one of those techniques which will be used greatly as you work on larger projects.

Standard Modules

By default, variables are local to the procedure in which they are created.

Variables can be changed or read only in the event procedure in which they were created.

Event procedures are also local to the form in which they were created.

For example, you can’t call the cmdQuit_Click event procedure from Form2 if the event was written in Form1.

Standard Modules

A standard module, or code module, is a special file that has the filename extension .bas and that contains variables and procedures that can be used anywhere in the program.

Just like forms, Standard Modules are listed separately in the Project window.

It can be saved to disk by using the Save Module1 As command on the File menu.

Unlike forms, Standard Modules contain no objects or property settings--only code that can be displayed and edited.

To create a new Standard Module, click on the Add Form button down arrow on the toolbar and click Module.

When you create a new Standard Module, it appears immediately in the Code window.

The first Module is name Module1, but you can change that.

To change the name of the module, click on the name property (the only property visible) and change the name.

Let’s change the name to modVariables

Let’s now save the Module by clicking on Save modVariables as from the File menu.

Working With Public Variables

After you declare the variable, you can read it, change it, or display it in any procedure in your program.

For example, the program statement Public RunningTotal would declare a public variable named RunningTotal in a standard module.

By default, public variables are declared as variant types in modules, but you can alter that.

For example: Public LastName As String woul d declare a public string variable named LastName in your program.

Let’s modify our Lotto picker to add a Public variable that counts how many picks we have made.

If we had declared our variable locally in the Command1_Click event procedure, the variable would have reset each time.

Using a public variable in a standard module lets us avoid hitting reset.

Creating General Purpose Procedures

A general -purpose procedure is like a built-in VB statement and function.

They are called by name, they can receive arguments, and each performs a specific task.

For example, imagine that a program has 3 mechanisms for printing a bit map:

A menu command named Print

A Print toolbar button

And a drag-and-drop printer icon

Instead of recreating that procedure 3 times, we can create one General-purpose procedure in a standard module.

General Purpose procedures save us time, make programs smaller and easier to handle, and make event procedures easier to read.

There are three types of general-purpose procedures in a standard module:

Function procedures

Sub Procedures

Property procedures

Function procedures are called by name from event procedures or other procedures.

They can also receive arguments, and they always return a value in the function name.

They are typically used for calculations.

Sub procedures are called by name from event procedures or other procedures.

Property procedures are used to create and manipulate user-defined properties in a program.

This is a useful feature that lets you customize existing VB controls and extend the VB language.

You need to be quite advanced to use this procedure.

The eliminate repeated lines.

Make programs easier to read.

Simplify program development.

Can be reused in other programs.

Extend the VB language

Writing Function Procedures

The statements do the meaningful work--processing text, handling input, or calculating a numeric value.

Writing Function Procedures

In other words, a Function procedure works just like using a built-in function such as Time, Int, or Str.

The basic syntax of a function is as follows:

Function FunctionName([arguments]) [As Type]

function statements

End Function

The following example computes the VAT tax and adds an EU tax.

Function TotalTax(Cost)

VatTax=Cost*.22

EuTax=Cost*.10

TotalTax=VatTax+EuTax

End Function

To call the TotalTax function in an event procedure, you would use a statement similar to the following:

lblTaxes.Caption=TotalTax(500)

This statement computes the total taxes required for a $500 item and then assigns the result to the Caption property of the lblTaxes object.

The TotalTax function can also take a variable as an argument, as shown below:

TotalCost=SalesPrice+TotalTax(SlaesPrice)

this line uses the TotalTax function to determine the taxes for the number in the SalesPrice variable and then adds them to SalesPrice to get the total cost of an item.

A sub procedure is similar to a Function procedure, except that a Sub doesn’t return a value associated with its name.

Subs are also used to process and return several variables during a procedure call.

Most functions can return only one value, but Sub procedures can return many.

Sub Procedure Syntax

Sub ProcedureName([arguments])

procedure statements

End Sub

By default, Sub procedures declared in a standard module are public, so they can be called by any event procedure.