Home > Articles > Programming > C/C++

Working with C++ Variables and Constants

Learn how to declare and define variables and constants, assign values to variables and manipulate those values, and write the value of a variable to the screen.
This sample chapter is excerpted from Sams Teach Yourself C++ in 21 Days, by Jesse Liberty.
This chapter is from the book

Programs need a way to store the data they use. Variables and constants offer various ways to represent, store, and manipulate that data.

Today you will 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?

In C++ a variable is a place to store information. 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.

Notice that this is temporary storage. When you turn the computer off, these variables are lost. Permanent storage is a different matter. Typically, variables are permanently stored either to a database or to a file on disk. Storing to a file on disk is discussed on Day 16, "Advanced Inheritance."

Data Is Stored in Memory

Your computer's memory can be viewed as a series of cubbyholes. Each cubbyhole is one of many, many such holes all lined up. Each cubbyhole—or memory location—is numbered sequentially. These numbers are known as memory addresses. A variable reserves one or more cubbyholes in which you may store a value.

Your variable's name (for example, myVariable) is a label on one of these cubbyholes so that you can find it easily without knowing its actual memory address. Figure 3.1 is a schematic representation of this idea. As you can see from the figure, myVariable starts at memory address 103. Depending on the size of myVariable, it can take up one or more memory addresses.

Figure 3.1 A schematic representation of memory.


RAM stands for Random Access Memory. When you run your program, it is loaded into RAM from the disk file. All variables are also created in RAM. When programmers talk about 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 what kind of variable it is: an integer, a character, and so forth. This information tells the compiler how much room to set aside and what kind of value you want to store in your variable.

Each cubbyhole is one byte large. If the type of variable you create is four bytes in size, it needs four bytes of memory, or four cubbyholes. The type of the variable (for example, integer) tells the compiler how much memory (how many cubbyholes) to set aside for the variable.

There was a time when it was imperative that programmers understood bits and bytes; after all, these are the fundamental units of storage. Computer programs have gotten better at abstracting away these details, but it is still helpful to understand how data is stored. For a quick review of the underlying concepts in binary math, please take a look at Appendix A, "Binary and Hexadecimal."


If mathematics makes you want to run from the room screaming, then don't bother with Appendix A; you won't really need it. The truth is that programmers no longer need to be mathematicians; though we do need to be comfortable with logic and rational thinking.

Size of Integers

On any one computer, each variable type takes up a single, unchanging amount of room. That is, an integer might be two bytes on one machine and four on another, but on either computer it is always the same, day in and day out.

A char variable (used to hold characters) is most often one byte long.


There is endless debate about how to pronounce char. Some say it as "car," some say it as "char"(coal), others say it as "care." Clearly, car is correct because that is how I say it, but feel free to say it however you like.

A short integer is two bytes on most computers, a long integer is usually four bytes, and an integer (without the keyword short or long) can be two or four bytes. You'd think the language would specify this exactly, but it doesn't. All it says is that a short must be less than or equal to the size of an int, which in turn must be less than or equal to the size of a long.

That said, you're probably working on a computer with a 2-byte short and a 4-byte int, with a 4-byte long.

The size of an integer is determined by the processor (16 bit or 32 bit) and the compiler you use. On modern 32-bit (Pentium) computers using modern compilers (for example, Visual C++ 4 or later), integers are four bytes. This book assumes a 4-byte integer, although your mileage may vary.

A character is a single letter, number, or symbol that takes up one byte of memory.

Compile and run Listing 3.1 on your computer and it will tell you the exact size of each of these types.

Listing 3.1  Determining the Size of Variable Types on Your Computer

  0:  #include <iostream>
  2:  int main()
  3:  {
  4:     using std::cout;
  6:     cout << "The size of an int is:\t\t"    
  7:        << sizeof(int)    << " bytes.\n";
  8:     cout << "The size of a short int is:\t" 
  9:        << sizeof(short)  << " bytes.\n";
 10:     cout << "The size of a long int is:\t"  
 11:        << sizeof(long)   << " bytes.\n";
 12:     cout << "The size of a char is:\t\t"    
 13:        << sizeof(char)   << " bytes.\n";
 14:     cout << "The size of a float is:\t\t"   
 15:         << sizeof(float)  << " bytes.\n";
 16:     cout << "The size of a double is:\t"    
 17:        << sizeof(double) << " bytes.\n";
 18:     cout << "The size of a bool is:\t"      
 19:        << sizeof(bool)   << " bytes.\n";
 21:     return 0;
 22:  }


The size of an int is:          4 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 float is:         4 bytes.
The size of a double is:        8 bytes.
The size of a bool is:          1 bytes.


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

Most of Listing 3.1 should be pretty familiar. I've split the lines to make them fit for the book, so for example, lines 6 and 7 could really be on a single line. The compiler ignores white space (spaces, tabs, line returns) and so treats these as a single line.

The one new feature in this program is the use of the sizeof() operator in lines 6-19. sizeof() is provided by your compiler, and it tells you the size of the object you pass in as a parameter. On line 7, for example, the keyword int is passed into sizeof(). Using sizeof(), I was able to determine that on my computer an int is equal to a long int, which is four bytes.

signed and unsigned

All integer types come in two varieties: signed and unsigned. The idea here is that 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. If this is confusing, be sure to read Appendix A.

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, although 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





1 byte

true or false

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

int (16 bit)

2 bytes

-32,768 to 32,767

int (32 bit)

4 bytes

-2,147,483,648 to 2,147,483,647

unsigned int (16 bit)

2 bytes

0 to 65,535

unsigned int (32 bit)

4 bytes 

0 to 4,294,967,295


1 byte

256 character values


4 bytes

1.2e-38 to 3.4e38


8 bytes

2.2e-308 to 1.8e308


The sizes of variables might be different from those shown in Table 3.1, depending on the compiler and the computer you are using. If your computer had the same output as was presented in Listing 3.1, Table 3.1 should apply to your compiler. If your output from Listing 3.1 was different, you should consult your compiler's manual for the values that your variable types can hold.

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