Microsoft Visual Basic 2010 Step by Step eBook

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Chapter 10

Creating Modules and Procedures

After completing this chapter, you will be able to:

n Employ structured programming techniques and create modules containing public

variables and procedure definitions.

n Practice using public variables that have a global scope.

n Increase programming efficiency by creating user-defined Sub and Function

procedures.

n Master the syntax for calling and using user-defined procedures.

n Pass arguments to procedures by value and by reference.

In the first nine chapters of this book, you have used event procedures such as Button1_Click,

Timer1_Tick, and Form1_Load to manage events and organize the flow of your programs.

In Microsoft Visual Basic programming, all executable statements must be placed inside

some procedure; only general declarations and instructions to the compiler can be placed

outside a procedure’s scope. In this chapter, you’ll continue to organize your programs by

breaking computing tasks into discrete logical units.

You’ll start by learning how to create modules, which are separate areas within a program

that contain global, or public, variables and Function and Sub procedures. You’ll learn how to

declare and use public variables, and you’ll learn how to build general-purpose procedures

that save coding time and can be used in more than one project. The skills you’ll learn will be

especially applicable to larger programming projects and team development efforts.

Working with Modules

As you write longer programs, you’re likely to have several forms and event procedures

that use some of the same variables and routines. By default, variables are local to an event

procedure—they can be read or changed only within the event procedure in which they

were created. You can also declare variables at the top of a form’s program code and give

the variables a greater scope throughout the form. However, if you create multiple forms in

a project, the variables declared at the top of a form are valid only in the form in which they

were declared. Likewise, event procedures are by default declared as private and are only

local to the form in which they are created. For example, you can’t call the Button1_Click

event procedure from a second form named Form2 if the event procedure is declared to be

private to Form1. (You’ll learn how to add additional forms to your project in Chapter 14,

“Managing Windows Forms and Controls at Run Time .”)

Table of Contents

Creating Modules and Procedures........................... 247

Working with Modules.............................................. 247

Creating a Module............................................. 248

Working with Public Variables........................................ 251

Creating Procedures................................................ 255

Writing Function Procedures......................................... 256

Function Syntax............................................... 257

Calling a Function Procedure.................................... 258

Using a Function to Perform a Calculation........................ 258

Writing Sub Procedures............................................. 262

Sub Procedure Syntax.......................................... 262

Calling a Sub Procedure........................................ 263

Using a Sub Procedure to Manage Input.......................... 264

One Step Further: Passing Arguments by Value

and by Reference................................................... 268

Chapter 10 Quick Reference.......................................... 270