Home > Articles > Programming > Windows Programming

  • Print
  • + Share This
This chapter is from the book

Writing Your Own Routines

Although the built-in functions are quite useful, there will always be times when you need to create your own routines. Perhaps you need to select a set of built-in functions that are all called in the same way, or perhaps you need to create some unique functionality. Either way, Visual Basic .NET makes creating your own routines easy.

There are two types of routines used in Visual Basic .NET. One type is a routine that does something, but doesn't return any value. These are called subroutines (or sub for short). The other type of procedure does something, but returns a value. These are called functions.

Subroutines

A subroutine is a block of Visual Basic .NET code that performs some task—for example, the Console.WriteLine method that you see in many of the examples. It prints information to the screen, but does not return any value. You use subroutines to perform tasks in your programs.

Generally, any time you have some code that you perform more than once, you should think about putting it into a subroutine. Similarly, if you have some code that you might use in multiple applications, you should put it into a subroutine. Subroutines let you isolate a small chunk of your program, so that rather than repeating the whole block of code, you simply refer to it by name. This does not mean that the subroutine will always do exactly the same steps, but that it will do some task. For example, a recipe might say, "Add one part vinegar to three parts oil." One time you might mix up one cup of vinegar to three cups of oil, whereas another time it might be only three tablespoons of vinegar to nine tablespoons of oil. Either way, you have performed the CreateVinaigrette subroutine. Yes, I'm making dinner as I write this.

To create your own subroutines, you use the Sub keyword:

Sub SubRoutineName(Parameter1 As Type, Parameter2 As Type, ... 
ParameterN As Type)
 'Do whatever in here
End Sub

In this syntax, each of the Parameters defines a value that is to be passed into the routine. Listing 3.2 shows declaring and using a subroutine.

Listing 3.2 Creating and Using a Subroutine

 1 Sub ShowMessage(ByVal Message As String)
 2   Console.WriteLine(Message)
 3 End Sub

 4 ShowMessage("Hello World from Visual Basic .NET")

Our subroutine begins with the Sub keyword, as on line 1. The subroutine is called ShowMessage, and takes one parameter when you call it. The subroutine ends with the End Sub keyword (line 3). In between is the actual code executed by the subroutine. In this case, it simply displays the contents of the parameter to the Console window. Line 4 shows one possible way of calling the subroutine, passing in the string "Hello World from Visual Basic .NET".

Functions

Creating your own functions enables you to create new capabilities within your application. Creating a new function is similar to defining new subroutines, except that you define the return value type. Within the procedure, you identify the value to be returned, as shown here:

Function FunctionName(Parameter1 As Type, ... ParameterN As Type) As ReturnType
 'Do whatever in here
 Return ReturnValue
End Function

In this syntax, each of the parameters defines a value that is to be passed into the routine, ReturnType is the data type the function returns, and ReturnValue is the value that will be returned from the function. Listing 3.3 shows the declaration and use of a simple function.

Listing 3.3 Creating and Using a Function

1 Function Volume(ByVal Length As Integer, _
2     ByVal Width As Integer, ByVal Height As Integer) As Integer
3  Return Length * Width * Height
4 End Function
5
6 Console.WriteLine(Volume(3,4,5))

Scope

Scope is one of those lovely computer-speak words that means, "Who else can see me?" Formally, scope defines the visibility of variables within a program, that is, which routines could use a given variable. You might not want all routines to access all variables. Allowing all routines to see all variables could lead to one routine "accidentally" changing the value of a variable, introducing a bug in your program.

Up until now, we have usually declared variables using the Dim keyword inside of procedures. However, you can also declare variables outside of procedures to make the variable available to multiple procedures. If you do this, you can use two other keywords, Public and Private:

  • Public variables are available throughout an application. These are Global variables, which exist globally, or throughout, the application. Public variables should be used sparingly, but are useful when you need some value that will be used at many points in your program, such as the connection to a database, or a file.

  • Private variables are available within the module or class where they are declared. Private variables are used frequently in applications when you need a single variable that can be used in multiple procedures. By creating it with the Private keyword, you allow all the procedures within one module or class to access the variable. Private variables are useful for sharing common information required for a task, such as an intermediate value that can be accessed by different functions to perform a calculation.

TIP

When you create a variable, you should declare it a newly created variable as close as possible to where it is needed. If you only use a variable in one procedure, you should declare that variable within that procedure.

Use module-level Private and Public variables sparingly.

Why Is Scope Important?

Scope enables you to isolate the data used by your applications' procedures. Much older versions of BASIC did not have the capability for scope, and all variables were accessible and changeable from all parts of the program. Imagine writing a program back then—you might often reuse (on purpose or accidentally) a variable elsewhere in a program. This could possibly lead to a bug if you changed the value in one spot in the program, only to mistakenly read the changed value later when you expected to get the original value.

Scope and Procedures

Just as variables can have scope, procedures (subroutines and functions) have scope. Scope for procedures means the same as scope for variables: It describes where else in your program you can use the procedure (or outside your program, as you'll see when you begin creating objects).

Procedure scope is defined using the same keywords used for variable scope. Generally, scope has the same meaning here as well.

  • Public The procedure can be called from any other part of the application. This is the default if you don't add any other keyword.

  • Private The procedure can only be called from another procedure within the same module or class where it is defined. This is useful when you are writing a number of support routines used throughout a calculation, but that other routines would not need to use.

Just as with variables, additional scope keywords apply when you are creating objects in Visual Basic .NET. We'll look at those keywords later.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020