Home > Articles > Programming > C/C++

Variables and Constants in C++

Learn the basics of variables and constants. Topics include built-in C++ types, defining a variable, and enumerated constants.
This chapter is from the book

Programs need a way to store the data they use. Variables and constants offer various ways to work with numbers and other values.

In this hour you learn:

  • How to declare and define variables and constants

  • How to assign values to variables and manipulate those values

  • How to write the value of a variable to the screen

What Is a Variable?

From a programmer's point of view, a variable is a location in your computer's memory in which you can store a value and from which you can later retrieve that value.

To understand this, you must first understand a bit about how computer memory works. Your computer's memory can be thought of as a series of cubby holes, all lined up in a long row. Each cubby hole—or memory location—is numbered sequentially. These numbers are known as memory addresses.

Variables not only have addresses, they have names. For example, you might create a variable named myAge. Your variable is a label on one of these cubby holes so that you can find it easily, without knowing its actual memory address.

Figure 3.1 is a visual representation of this idea. As you can see from the figure, we've declared a variable named myVariable. myVariable starts at memory address 103.

Figure 3.1 A visual representation of memory.

New Term

RAM is Random Access Memory. It is the electronic memory your computer uses while executing programs. Any information in RAM is lost when your computer is turned off. When you run your program, it is loaded into RAM from the disk file (hard drive storage). All variables are created in RAM as well. When programmers talk of memory, it is usually RAM to which they are referring.

Setting Aside Memory

When you define a variable in C++, you must tell the compiler not only what its name is, but also what kind of information it will hold: integer, character, and so forth. This is the variable's type. The type of the variable tells the compiler how much room to set aside in memory to hold the variable's value.

Each cubby is one byte large. If the type of variable you create is two bytes in size, it needs two bytes of memory, or two cubbies. The type of the variable (for example, int) tells the compiler how much memory (how many cubby holes) to set aside for the variable. Because computers use bits and bytes to represent values, and because memory is measured in bytes, it is important that you understand and are comfortable with these concepts.

Size of Integers

A char variable (used to hold characters) is most often one byte long. A short int is two bytes on most computers; a long int is usually four bytes, and an int (without the keyword short or long) can be two or four bytes. If you are running Windows 95, Windows 98, or Windows NT, you can count on your int being four bytes as long as you use a modern compiler.

Listing 3.1 will help you determine the exact size of these types on your computer using your particular compiler.

Listing 3.1 Determines the Size of Variable Types on Your Computer.

 0: #include <iostream>
 2: int main()
 3: {
 4:   std::cout << "The size of an int is:\t\t";
 5:   std::cout << sizeof(int) << " bytes.\n";
 6:   std::cout << "The size of a short int is:\t"; 
 7:   std::cout << sizeof(short) << " bytes.\n";
 8:   std::cout << "The size of a long int is:\t";
 9:   std::cout << sizeof(long) << " bytes.\n";
 10:   std::cout << "The size of a char is:\t\t";
 11:   std::cout << sizeof(char) << " bytes.\n";
 12:   std::cout << "The size of a float is:\t\t";
 13:   std::cout << sizeof(float) << " bytes.\n";
 14:   std::cout << "The size of a double is:\t";
 15:   std::cout << sizeof(double) << " bytes.\n";
 17:   return 0;
 18: }


The size of an int is        2 bytes.
The size of a short int is   2 bytes.
The size of a long int is    4 bytes.
The size of a char is        1 bytes.
The size of a bool is        1 bytes.

The size of a float is       4 bytes.
The size of a double is      8 bytes.


On your computer, the number of bytes presented might be different!

Analysis - Most of Listing 3.1 will be familiar. The one new feature is the use of the sizeof() function in lines 5 through 15. sizeof() is provided by your compiler, and it tells you the size of the object you pass in as a parameter. For example, on line 5 the keyword int is passed into sizeof(). Using sizeof(), I was able to determine that on my computer, an int is equal to a short int, which is two bytes.

signed and unsigned

In addition, all these types come in two varieties: signed and unsigned. Sometimes you need negative numbers, and sometimes you don't. Integers (short and long) without the word "unsigned" are assumed to be signed. signed integers are either negative or positive. unsigned integers are always positive.

Because you have the same number of bytes for both signed and unsigned integers, the largest number you can store in an unsigned integer is twice as big as the largest positive number you can store in a signed integer. An unsigned short integer can handle numbers from 0 to 65,535. Half the numbers represented by a signed short are negative, thus a signed short can only represent numbers from –32,768 to 32,767.

Fundamental Variable Types

Several other variable types are built into C++. They can be conveniently divided into integer variables (the type discussed so far), floating-point variables, and character variables.

Floating-point variables have values that can be expressed as fractions—that is, they are real numbers. Character variables hold a single byte and are used for holding the 256 characters and symbols of the ASCII and extended ASCII character sets.

The ASCII character set is the set of characters standardized for use on computers. ASCII is an acronym for American Standard Code for Information Interchange. Nearly every computer operating system supports ASCII, though many support other international character sets as well.

The types of variables used in C++ programs are described in Table 3.1. This table shows the variable type, how much room this book assumes it takes in memory, and what kinds of values can be stored in these variables. The values that can be stored are determined by the size of the variable types, so check your output from Listing 3.1.

Table 3.1 Variable Types




unsigned short int

2 bytes

0 to 65,535

short int

2 bytes

–32,768 to 32,767

unsigned long int

4 bytes

0 to 4,294,967,295

long int

4 bytes

–2,147,483,648 to 2,147,483,647


4 bytes

–2,147,483,648 to 2,147,483,647

unsigned int

4 bytes

0 to 4,294,967,295


1 byte

-256 character values


1 byte

true or false


4 bytes

1.2e–38 to 3.4e38


8 bytes

2.2e–308 to 1.8e308

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