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.
We will learn
about all the data types in detail in the next tutorial.
The value of a variable
can be changed, hence the name variable.
int age
= 14; // age is 14
age
= 17; // age is 17
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
cannot 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.
Note: We should try to
give meaningful names to variables. For example, first_name is a better variable
name than fn.
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.
Here's a list
of different literals in C++ programming.
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:-2.0
0.0000234
-0.22E-5
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. 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 |
We will learn
about strings in detail in the C++ string tutorial.
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.
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