Home > Articles

This chapter is from the book

Looping Logic

Loops allow you to perform an action over and over again until some condition is met. There are three types of loops in VB.NET and C#: While, Do, and For.

While Loops

While loops are useful when you know don't know how many times you need to do something, such as when you want to loop through an unknown number of cars until you run into a Mercedes. These loops are based on conditional expressions, and they continue to run until the condition becomes false. The syntax for a while loop in VB.NET is as follows:

While condition
End While

In C#:

while (condition) {

For example, the following code counts from 1 to 10 and prints out the number to the browser:

int intCount = 1;
while (intCount < 10) {
  Response.Write(intCount + "<br>");
  intCount += 1;

On the second line, the program checks if intCount is greater than 10. It shouldn't be, because you just set it to be equal to 1. The program executes the code inside the while loop, writing the number to the browser and adding 1 to intCount. It then goes back to the second line and checks if intCount is now greater than 10. intCount is 2 now, so the loop continues. When it finishes, you'll see the numbers 1 through 9 displayed in the browser. Figure 3.5 illustrates this process.

Figure 3.5 The looping process.

Why do we use 9 instead of 10? Once intCount hits 10, the statement on line 2 is no longer true—it evaluates to false—so the loop exits and continues after line 5.

The do loop is the same as the while loop; the syntax is just slightly different. The do loop comes in many forms, such as the following:

Loop While condition

do {
} while condition

Here's another one:

Do While condition

The different forms produce different output depending on how many times you want them to execute. Let's look at an example of each:

dim intCount as Integer = 10
  Response.Write(intCount & "<br>")
  intCount = intCount + 1
Loop While intCount < 10 

Do While intCount < 10
  Response.Write(intCount & "<br>")
  intCount = intCount + 1

The first loop prints out the number 10, while the second loop prints out nothing. Why? The first loop evaluates the condition on the last line of the loop. Therefore, the code inside the loop will be executed once no matter what. The second loop evaluates the condition right up front, and in this case it stops the code from ever executing.

You should use a Do loop when you want the code inside the block to execute at least once. Conversely, you should use a Do While loop if you don't care whether the code is executed at all. In VB.NET, you can also use until in place of while:

dim intCount as Integer = 1
  Response.Write(intCount & "<br>")
  intCount = intCount + 1
Loop Until intCount >= 10 

This loop does exactly the same thing as the first loop in the previous listing. The difference is that using until will let the loop go until the condition is true, whereas using while stops when the condition is false. In this case, the loop stops when intCount is greater than or equal to 10.

For Loops

Use a for loop when you know how many times you want to execute your code. This loop increments a counter to tell itself when to stop executing. The for loop syntax is as follows:

For variable = startvalue To stopvalue [Step step-size]
Next [variable]

for (variable = startvalue; variable comparison stopvalue; step) {

This loop uses the step-size to increment variable until it reaches the stopvalue, at which point the loop stops executing. (In VB.NET, you can leave the step parameter out if you want—it defaults to a value of 1.) For example:

For intCount = 1 to 10 
  Response.Write(intCount & "<br>")


For intCount = 10 to 1 step –1
  Response.Write(intCount & "<br>")

The first loop prints out the numbers 1 through 10, while the second prints them in reverse order.

In C#, the previous code snippet would be

for (intCount = 10; intCount == 1; intCount--) {
  Response.Write(intCount + "<br>");

Another form of the for loop is the for...each loop (foreach in C#). This loop iterates through all of the items in a collection, such as an array. For example:

dim arrWeekDays() as String = {"Monday", "Tuesday", _
  "Wednesday", "Thursday", "Friday"}

For Each strDay in arrWeekDays
  Response.Write(strDay & "<br>")

On the first line, you create an array of strings containing the weekdays. On the fourth line, you loop through each item in the array. The variable strDay is simply a counter that the loop uses—you could specify any variable here. The loop assigns each variable in the array to strDay, and you print that value out on the fifth line. The result is that the days of the week are displayed in the browser, as shown in Figure 3.6.

Figure 3.6 Using a for...each loop to iterate over the items in an array.

Infinite Loops

Notice that you had to manually increment the counter in your while and do loops, whereas the for loops did so automatically. It's very important to increment your counter in these loops. Otherwise, you'd end up with an infinite loop—a loop that never exits. Not only is this a pain for visitors to your site, but it also drains system resources very quickly and can cause the site to crash.

If you ever need to exit a loop before it finishes, you can use the exit (break in C#) keyword to stop the loop. The syntax for this keyword in VB.NET depends on where you use it. For example:

Do While intCount < 10
  Response.Write(intCount & "<br>")
  intCount = intCount + 1
  if intCount = 7 then
   exit do
  end if

For intCount = 1 to 10 
  Response.Write(intCount & "<br>")
  if intCount = 7 then
   exit for
  end if

The first loop iterates through the numbers 1 through 10, but if the number equals 7 (which it eventually will, in this case), you stop the loop by using exit do (note that it prints out only 1–6). The second loop does exactly the same thing, but using exit for (this one prints out 1–7). The exit statement that's used will depend on the type of loop you're in.

In C#, the syntax doesn't change no matter where the keyword is used:

for (intCount = 1; intCount == 10; intCount++) {
  Response.Write(intCount + "<br>");
  if (intCount == 7) {

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.


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.


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.


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.


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


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


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.


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.


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