Home > Articles > Programming > C/C++

  • Print
  • + Share This
This chapter is from the book 1.3. Hello Who?

1.3. Hello Who?

Now that we have seen how to build the hello program we will look at its source code. Don’t worry about understanding all the details—everything shown in this chapter (and much more!) is covered thoroughly in the subsequent chapters. Here is the complete hello program (in file hello/hello.go):


Go uses C++-style comments: // for single-line comments that finish at the end of the line and /* ... */ for comments that can span multiple lines. It is conventional in Go to mostly use single-line comments, with spanning comments often used for commenting out chunks of code during development.4

Every piece of Go code exists inside a package, and every Go program must have a main package with a main() function which serves as the program’s entry point, that is, the function that is executed first. In fact, Go packages may also have init() functions that are executed before main(), as we will see (§1.7, → 40); full details are given later (§5.6.2, → 222). Notice that there is no conflict between the name of the package and the name of the function.

Go operates in terms of packages rather than files. This means that we can split a package across as many files as we like, and from Go’s point of view if they all have the same package declaration, they are all part of the same package and no different than if all their contents were in a single file. Naturally, we can also break our applications’ functionality into as many local packages as we like, to keep everything neatly modularized, something we will see in Chapter 9.

The import statement (14 ←, ➊) imports three packages from the standard library. The fmt package provides functions for formatting text and for reading formatted text (§3.5, → 93), the os package provides platform-independent operating-system variables and functions, and the strings package provides functions for manipulating strings (§3.6.1, → 106).

Go’s fundamental types support the usual operators (e.g., + for numeric addition and for string concatenation), and the Gostandard library supplements theseby providing packages of functions for working with the fundamental types, such as the stringspackage imported here. It is also possible to create our own custom types based on the fundamental types and to provide our own methods—that is, custom type-specific functions—for them. (We will get a taste of this in §1.5, → 21, with full coverage in Chapter 6.)

The reader may have noticed that the program has no semicolons, that the imports are not comma-separated, and that the if statement’s condition does not require parentheses. In Go, blocks, including function bodies and control structure bodies (e.g., for if statements and for for loops), are delimited using braces. Indentation is used purely to improve human readability. Technically, Go statements are separated by semicolons, but these are put in by the compiler, so we don’t have to use them ourselves unless we want to put multiple statements on the same line. No semicolons and fewer commas and parentheses give Go programs a lighter look and require less typing.

Go functions and methods are defined using the func keyword. The main package’s main() function always has the same signature—it takes no arguments and returns nothing. When main.main()finishes the program will terminate and return 0 to the operating system. Naturally, we can exit whenever we like and return our own choice of value, as we will see (§1.4, → 16).

The first statement in the main() function (14 , ➋; using the := operator) is called a short variable declaration in Go terminology. Such a statement both declares and initializes a variable at the same time. Furthermore, we don’t need to specify the variable’s type because Go can deduce that from the initializing value. So in this case we have declared a variable called who of type string, and thanks to Go’s strong typing we may only assign strings to who.

As with most languages the if statement tests a condition—in this case, how many strings were entered on the command-line—which if satisfied executes the corresponding brace-delimited block. We will see a more sophisticated if statement syntax later in this chapter (§1.6, → 29), and further on (§5.2.1, → 190).

The os.Args variable is a slice of strings (14 , ➌). Arrays, slices, and other collection data types are covered in Chapter 4 (§4.2, → 146). For now it is sufficient to know that a slice’s length can be determined using the built-in len() function and its elements can be accessed using the [] index operator using a subset of the Python syntax. In particular, slice[n] returns the slice’s nth element (counting from zero), and slice[n:] returns another slice which has the elements from the nth element to the last element. In the collections chapter we will see the full generality of Go’s syntax in this area. In the case of os.Args, the slice should always have at least one string (the program’s name), at index position 0. (All Go indexing is 0-based.)

If the user has entered one or more command line arguments the if condition is satisfied and we set the who string to contain all the arguments joined up as a single string (14 ←, ➍). In this case we use the assignment operator (=), since if we used the short variable declaration operator (:=) we would end up declaring and initializing a new who variable whose scope was limited to the if statement’s block. The strings.Join() function takes a slice of strings and a separator (which could be empty, i.e., ""), and returns a single string consisting of all the slice’s strings with the separator between each one. Here we have joined them using a single space between each.

Finally, in the last statement (14←, →), we print Hello, a space, the string held in the who variable, and a newline. The fmt package has many different print variants, some like fmt.Println() which will neatly print whatever they are given, and others like fmt.Printf() that use placeholders to provide very fine control over formatting. The print functions are covered in Chapter 3 (§3.5, → 93).

The hello program presented here has shown far more of the language’s features than such programs conventionally do. The subsequent examples continue in this vein, covering more advanced features while keeping the examples as short as possible. The idea here is to simply acquire some basic familiarity with the language and to get to grips with building, running, and experimenting with simple Go programs, while at the same time getting a flavor of Go’s powerful and novel features. And, of course, everything presented in this chapter is explained in detail in the subsequent chapters.

  • + 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