C++ Variables, Literals and Constants

In the previous tutorial you learnt about C++ comments. Now, let's learn about variables, constants and literals in C++.

C++ Variables

In programming, a variable is a container (storage area) to hold data.

To indicate the storage area, each variable should be given a unique name (identifier). For example,

int age = 14;

Here, age is a variable of the int data type, and we have assigned an integer value 14 to it.

The value of a variable can be changed, hence the name variable.

int age = 14;   // age is 14
age = 17;       // age is 17

Visit this page to learn more about different types of data a variable can store.

Rules for naming a variable
  1. A variable name can only have alphabets, numbers, and the underscore _.
  2. A variable name cannot begin with a number.
  3. It is a preferred practice to begin variable names with a lowercase character. For example, name is preferable to Name.
  4. A variable name cannot be a keyword. For example, int is a keyword that is used to denote integers.
  5. A variable name can start with an underscore. However, it's not considered a good practice.

Note: We should try to give meaningful names to variables. For example, first_name is a better variable name than fn.

C++ Constants

In C++, we can create variables whose value cannot be changed. For that, we use the const keyword. Here's an example:

const int LIGHT_SPEED = 299792458;
LIGHT_SPEED = 2500 // Error! LIGHT_SPEED is a constant.

Here, we have used the keyword const to declare a constant named LIGHT_SPEED. If we try to change the value of LIGHT_SPEED, we will get an error.

A constant can also be created using the #define preprocessor directive. We will learn about it in detail in the C++ Macros tutorial.

C++ Literals

Literals are data used for representing fixed values. They can be used directly in the code. For example: 1, 2.5, 'c' etc.

Here, 1, 2.5 and 'c' are literals. Why? You cannot assign different values to these terms.

1. Integers

An integer is a numeric literal(associated with numbers) without any fractional or exponential part. There are three types of integer literals in C++ programming:

  • decimal (base 10)
  • octal (base 8)
  • hexadecimal (base 16)

For example:

Decimal: 0, -9, 22 etc

Octal: 021, 077, 033 etc

Hexadecimal: 0x7f, 0x2a, 0x521 etc

In C++ programming, octal starts with a 0, and hexadecimal starts with a 0x.

2. Floating-point Literals

A floating-point literal is a numeric literal that has either a fractional form or an exponent form. For example:




Note: E-5 = 10-5

3. Characters

A character literal is created by enclosing a single character inside single quotation marks. For example: 'a', 'm', 'F', '2', '}' etc.

4. String Literals

A string literal is a sequence of characters enclosed in double-quote marks. For example:

"good" string constant
"" null string constant
" " string constant of six white space
"x" string constant having a single character
"Earth is round\n" prints string with a newline

We will learn about strings in detail in the C++ string tutorial.

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