Home > Articles > Programming > C/C++

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


Although main() is a function, it is an unusual one. To be useful, a function must be called, or invoked, during the course of your program. main() is invoked by the operating system.

A program is executed line-by-line in the order it appears in your source code until a function is reached. Then the program branches off to execute the function. When the function finishes, it returns control to the line of code immediately following the call to the function.

A good analogy for this is sharpening your pencil. If you are drawing a picture and your pencil point breaks, you might stop drawing, go sharpen the pencil, and then return to what you were doing. When a program needs a service performed, it can call a function to perform the service and then pick up where it left off when the function is finished running. Listing 2.6 demonstrates this idea.

Listing 2.6. Demonstrating a Call to a Function

  1:  #include <iostream>
  3:  // function Demonstration Function
  4:  // prints out a useful message
  5:  void DemonstrationFunction()
  6:  {
  7:      std::cout << "In Demonstration Function\n";
  8:  }
 10:  // function main - prints out a message, then
 11:  // calls DemonstrationFunction, then prints out
 12:  // a second message.
 13:  int main()
 14:  {
 15:      std::cout << "In main\n" ;
 16:      DemonstrationFunction();
 17:      std::cout << "Back in main\n";
 18:      return 0;
 19:  }


In main
In Demonstration Function
Back in main


The function DemonstrationFunction() is defined on lines 6–8. When it is called, it prints a message to the console screen and then returns.

Line 13 is the beginning of the actual program. On line 15, main() prints out a message saying it is in main(). After printing the message, line 16 calls DemonstrationFunction(). This call causes the flow of the program to go to the DemonstrationFunction() function on line 5. Any commands in DemonstrationFunction() are then executed. In this case, the entire function consists of the code on line 7, which prints another message. When DemonstrationFunction() completes (line 8), the program flow returns to from where it was called. In this case, the program returns to line 17, where main() prints its final line.

Using Functions

Functions either return a value or they return void, meaning they do not return anything. A function that adds two integers might return the sum, and thus would be defined to return an integer value. A function that just prints a message has nothing to return and would be declared to return void.

Functions consist of a header and a body. The header consists, in turn, of the return type, the function name, and the parameters to that function. The parameters to a function enable values to be passed into the function. Thus, if the function were to add two numbers, the numbers would be the parameters to the function. Here’s an example of a typical function header that declares a function named Sum that receives two integer values (first and second) and also returns an integer value:

int Sum( int first, int second)

A parameter is a declaration of what type of value will be passed in; the actual value passed in when the function is called is referred to as an argument. Many programmers use the terms parameters and arguments as synonyms. Others are careful about the technical distinction. The distinction between these two terms is not critical to your programming C++, so you shouldn’t worry if the words get interchanged.

The body of a function consists of an opening brace, zero or more statements, and a closing brace. The statements constitute the workings of the function.

A function might return a value using a return statement. The value returned must be of the type declared in the function header. In addition, this statement causes the function to exit. If you don’t put a return statement into your function, it automatically returns void (nothing) at the end of the function. If a function is supposed to return a value but does not contain a return statement, some compilers produce a warning or error message.

Listing 2.7 demonstrates a function that takes two integer parameters and returns an integer value. Don’t worry about the syntax or the specifics of how to work with integer values (for example, int first) for now; that is covered in detail in Lesson 3.

Listing 2.7. FUNC.cpp Demonstrates a Simple Function

  1:  #include <iostream>
  2:  int Add (int first, int second)
  3:  {
  4:      std::cout << "Add() received "<< first << " and "<< second << "\n";
  5:      return (first + second);
  6:  }
  8:  int main()
  9:  {
 10:      using std::cout;
 11:      using std::cin;
 14:      cout << "I'm in main()!\n";
 15:      int a, b, c;
 16:      cout << "Enter two numbers: ";
 17:      cin >> a;
 18:      cin >> b;
 19:      cout << "\nCalling Add()\n";
 20:      c=Add(a,b);
 21:      cout << "\nBack in main().\n";
 22:      cout << "c was set to " << c;
 23:      cout << "\nExiting...\n\n";
 24:      return 0;
 25:  }


I'm in main()!
Enter two numbers: 3 5

Calling Add()
In Add(), received 3 and 5

Back in main().
c was set to 8


The function Add() is defined on line 2. It takes two integer parameters and returns an integer value. The program itself begins on line 8. The program prompts the user for two numbers (line 16). The user types each number, separated by a space, and then presses the Enter key. The numbers the user enters are placed in the variables a and b on lines 17 and 18. On line 20, the main() function passes the two numbers typed in by the user as arguments to the Add() function.

Processing branches to the Add() function, which starts on line 2. The values from a and b are received as parameters first and second, respectively. These values are printed and then added. The result of adding the two numbers is returned on line 5, at which point the function returns to the function that called it—main(), in this case.

On lines 17 and 18, the cin object is used to obtain a number for the variables a and b. Throughout the rest of the program, cout is used to write to the console. Variables and other aspects of this program are explored in depth in the next lesson.

Methods Versus Functions

A function by any other name is still just a function. It is worth noting here that different programming languages and different programming methodologies might refer to functions using a different term. One of the more common words used is method. Method is simply another term for functions that are part of a class.

  • + 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.


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