Variables Literals Constants

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. 

Note: The int data type suggests that the variable can only hold integers. Similarly, we can use the double data type if we have to store decimals and exponentials.

Rules for naming a variable

• A variable name can only have alphabets, numbers, and the underscore _.
• A variable name cannot begin with a number.
• Variable names should not begin with an uppercase character.
• A variable name cannot be a keyword. For example, int is a keyword that is used to denote integers.
• A variable name can start with an underscore. However, it's not considered a good practice.

 

 Literals

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

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

 

2. Floating-point Literals

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

-2.0

0.0000234

3. Characters

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

4. Escape Sequences

Sometimes, it is necessary to use characters that cannot be typed or has special meaning in C++ programming. For example, newline (enter), tab, question mark, etc.

In order to use these characters, escape sequences are used.

Escape Sequences	Characters
\b	Backspace
\f	Form feed
\n	Newline
\r	Return
\t	Horizontal tab
\v	Vertical tab
\\	Backslash
\'	Single quotation mark
\"	Double quotation mark
\?	Question mark
\0	Null Character

5. 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

 

 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.