Microsoft Visual Basic 2010 Step by Step eBook

270 Part II Programming Fundamentals

By declaring Cost using ByVal, you can safely modify Cost in the CostPlusInterest procedure

without sending the changes back to the calling procedure. By keeping Total declared using

ByRef, you can modify the variable that’s being passed, and only those changes will be

passed back to the calling procedure. In general, if you use ByRef only when it’s needed, your

programs will be freer of defects.

Here are some guidelines on when to use ByVal and when to use ByRef:

n Use ByVal when you don’t want a procedure to modify a variable that’s passed to the

procedure through an argument.

n Use ByRef when you want to allow a procedure to modify a variable that’s passed to

the procedure through an argument.

n When in doubt, use the ByVal keyword.

Chapter 10 Quick Reference

To Do This

Create a new

module

Click the Add New Item button on the Standard toolbar, and then select

the Module template;

or

Click the Add New Item command on the Project menu, and then select

the Module template.

Rename a module Select the module in Solution Explorer. In the Properties window, specify

a new name in the File Name property;

or

Right-click the module in Solution Explorer, select Rename, and then

specify a new name.

Remove a module

from a program

Select the module in Solution Explorer, and then click the Exclude From

Project command on the Project menu.

Add an existing

module to a project

On the Project menu, click the Add Existing Item command.

Create a public

variable

Declare the variable by using the Public keyword between the Module

and End Module keywords in a module. For example:

Public TotalSales As Integer

Create a public

function

Place the function statements between the Function and End Function

keywords in a module. Functions are public by default. For example:

Function HitRate(ByVal Hits As Short, ByVal _

Tries As Short) As String

Dim Percent As Single

Percent = Hits / Tries

Return Format(Percent, "0.0%")

End Function