Home > Articles > Programming > C#

Like this article? We recommend

Like this article? We recommend

C# Loops

It's often necessary to perform a sequence of logic multiple times in a program. For example, there might be a list of some items where each item needs the same processing. This processing is performed with language constructs called loops. In C#, there are four types of loops—the while loop, the do loop, the for loop, and the foreach loop. Each has its own benefits for certain tasks.

while Loops

If it's necessary to continually execute a group of statements while a condition is true, use the while loop. The general form of the while loop is as follows:

  While (Boolean expression)
    true condition statement(s)

When the Boolean expression evaluates to true, the true condition statements are executed. The following example shows how a while loop can be used:

string doAgain = "Y";
int count = 0;
string[] siteName = new string[10];

while (doAgain == "Y")
 Console.Write("Please Enter Site Name: ");
 siteName[count++] = Console.ReadLine();

 Console.Write("Add Another?: ");
 doAgain = Console.ReadLine();

A sneaky bug to watch out for with all loops is the empty statement bug. The following code is for illustrative purposes only, so don't try it:

string doAgain = "Y";

while (doAgain == "Y"); // loop forever
 // this is never executed

Because curly braces are optional, the semicolon after the Boolean expression represents the true condition statement. Thus, every time the Boolean expression evaluates to true, the empty statement is executed and the Boolean statement is evaluated again—ad infinitum.

The reason the curly braces don't cause a bug is because they represent a block, which is legal syntax in C#.


A single semicolon is interpreted as a statement. A common mistake is to put a semicolon after a loop statement, which causes subsequent loop statements to execute only one time. These are hard-to-find errors.

do Loops

while loops evaluate an expression before executing the statements in a block. However, it may be necessary to execute the statements at least one time. This is what the do loop allows. Here's its general form:

  do {
  } while (Boolean expression);

The statements execute, and then the Boolean expression is evaluated. If the Boolean expression evaluates to true, the statements are executed again. Otherwise, control passes to the statement following the entire do loop. The following is an example of a do loop in action:

 Console.WriteLine("A - Add Site");
 Console.WriteLine("S - Sort List");
 Console.WriteLine("R - Show Report\n");

 Console.WriteLine("Q - Quit\n");

 Console.Write("Please Choose (A/S/R/Q): ");

 choice = Console.ReadLine();

 switch (choice)
  case "a":
  case "A":
   Console.WriteLine("Add Site");
  case "s":
  case "S":
   Console.WriteLine("Sort List");
  case "r":
  case "R":
   Console.WriteLine("Show Report");
  case "q":
  case "Q":

} while ((choice = choice.ToUpper()) != "Q"); 

This code snippet prints a menu and then asks the user for input. For this purpose, it is logical to use a do loop because the menu has to print at least one time. If this were to be done with another type of loop, some artificial condition would have needed to be set just to get the first iteration.

for Loops

for loops are good for when the number of times to execute a group of statements is known beforehand. Here's its general syntax:

  for (initializer; Boolean expression; modifier)

The initializer is executed one time only, when the for loop begins. After the initializer executes, the Boolean expression is evaluated. The Boolean expression must evaluate to true for the statement(s) to be executed. Once the statement(s) have executed, the modifier executes and then the Boolean expression is evaluated again. The statement(s) continue to be executed until the Boolean expression evaluates to false, after which control transfers to the statement following the for loop. The following example illustrates how to implement a for loop:

int n = siteName.Length-2;
int j, k;
string save;

for (k=n-1; k >= 0; k--)
 j = k + 1;
 save = siteName[k];
 siteName[n+1] = save;

 while ( String.Compare(save, siteName[j]) > 0 )
  siteName[j-1] = siteName[j];
 siteName[j-1] = save;

The insertion sort in this code shows how a for loop is used in a realistic scenario. Often, for loops begin at 0 and are incremented until a predetermined number of iterations have passed. This particular example starts at the end of the array and moves backward, decrementing each step. When k reaches 0, the loop ends.

For C++ Programmers

In Standard C++, for loop initializer declarations define a new scope for a variable with the same name in its enclosing block. In C#, this would be flagged as an error because a variable in the for loop initializer is not allowed to hide a variable with the same name in an enclosing block.

When programming in C#, there is a full set of libraries from which to choose premade functions. The Boolean condition of the while loop shows the String.Compare() method. In this particular instance, the program checks to see if save is greater than siteName[j]. If so, the Boolean result is true.

foreach Loops

The foreach loop is excellent for iterating through collections. Here's its syntax:

  foreach (type identifier in collection)

The type can be any C# or user-defined type. the identifier is the variable name that you want to use. The collection could be any C# collection object or array.

For C++ and Java Programmers

C++ and Java do not have a foreach loop.

Upon entering the foreach loop, the identifier variable is set with an item from the collection. Then the statement(s) are executed and control transfers back to get another item from the collection. When all items in the collection have been extracted, control transfers to the statement following the foreach loop.

Here's an example that iterates through the siteName array, printing each entry to the console.

foreach(string site in siteName)
 Console.WriteLine("\t{0}", site);

Had this been done with another loop, the program would have taken more effort. Then there's always the possibility of corrupting a counter. The foreach loop is a clean and simple way to iterate through an array.

The foreach loop was specially designed to work with collections. There are several collections in the System libraries, and Array is a built-in collection.

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