## Quick links

Constant values used within a program are known as Literals. These constant values occupy memory but do not have any reference like variables. Or as Wikipedia speaks literal is a notation for representing a fixed value within a source code.

There are four types of literals in C programming.

**Note: ** Literals are constant values not constant variables.

## Integer literal

In C programming we can specify an integer constant in three ways.

- Decimal number (base 10).
- Octal number (base 8).
- Hexadecimal number (base 16).

Integer literal is followed by an optional size or sign qualifier.

`l`

or `L`

is a size qualifier. It specifies size of an integer type as long.

`u`

or `U`

is a sign qualifier. It specifies an integer type as unsigned (can store only positive values).

Decimal constant is defined using digits between `0-9`. For example: 123.

Octal constants is prefixed with `0` followed by digits between `0-7`. For example: 0123 (in octal) equivalent to 83 in decimal. Always be cautious while defining octal constants, any number begins with 0 must only contain digits between 0-7 otherwise compiler will report an error on compilation. In addition, do not confuse octal constants as a decimal constant. For example: you might think 012 as a decimal constant 12, but it is an octal constant equivalent to 10 (in decimal).

Hexadecimal constant is prefixed with `0x` or `0X` following hexadecimal characters (i.e. digits from `0-9` and characters from `a-f` or `A-F`). For example: `0X1A` or `0x1a` or `0x1A` (in hexadecimal) equivalent to 26 (in decimal).

Valid examples of defining integer constant

In Decimal | In Octal | In Hexadecimal | Description |
---|---|---|---|

`2016u` | `03740u` | `0x7E0u` | Unsigned integer |

`2016U` | `03740U` | `0x7E0U` | |

`2147483697l` | `020000000061l` | `0x80000031l` | Long integer |

`2147483697L` | `020000000061L` | `0x80000031L` | |

`2147483697ul` | `020000000061ul` | `0x80000031ul` | Unsigned long integer |

`2147483697uL` | `020000000061uL` | `0x80000031uL` | |

`2147483697Ul` | `020000000061Ul` | `0x80000031Ul` | |

`2147483697UL` | `020000000061UL` | `0x80000031UL` |

**Note:** Order of the qualifiers doesn’t matter means `ul`

or `lu`

both are same.

Do not get puzzled with qualifiers. I will cover them in depth in data types.

## Float or real literal

In C programming a float or real constant is specified either using decimal or using exponential notation.

### Decimal notation

In decimal notation real constant is represented as whole number, followed by an optional decimal point and fractional part. It may be preceded with `+`

or `-`

symbol representing negative or positive number.

Valid examples of float constants in decimal notation.

`+1` `1.2` `-0.4` `0.` `.3` `-.3`

### Exponential notation

Exponential notations are helpful in representing any number with very big or small magnitude. Numbers such as, `7850000000000` in exponential notation expressed as `7.85e12`, `0.0000000000785` expressed as `7.85e-011`.

In exponential notation real constants are expressed in scientific format specifying mantissa and exponent. Valid syntax of writing real constant in scientific format.

`[+/-] <Mantissa> <e/E> [+/-] <Exponent>`

Valid examples of real constants in exponential notation

`0.1e1` `0e-5` `5e25` `+5E+10` `-5.2e0`

#### Rules for representation of real constant in exponential notation

- Mantissa can be expressed either as decimal or as fractional number.
- We can use either uppercase or lowercase for exponent sign i.e.
`E`or`e`. - Exponent must be a decimal value.
- A
`+`

or`-`

sign symbol may be prefixed before exponent and mantissa. - Spaces are not allowed.

## Character literal

Character literal is a single character constant enclosed within single quotes. In C programming character constant occupies single byte space in memory.

There are many ways to represent a character constant in C programming.

- Using character inside single quote. For example,
`‘a’``‘0’``‘/’``‘.’`etc. - Using escape sequence characters. For example,
`‘\n’``‘\a’``‘\b’`etc. - Using an integer ASCII representing of a character. For example,
`65`in ASCII format is used to represent`‘A’`. - Using octal or hexadecimal representation of integer as escape sequence character. For example,
`\05``\xA` - Using Unicode value of a character. For example,
`\u00A9`

### Multi-character constant

Character constant containing more than one character inside single quote is known as multi-character constant. The compiler won’t complain if you give multi-character constant in single quote which is generally not practiced.

For example, `'abcd'` is a valid character constant in C. However, it will only represent last character of the constant i.e. `'d'` in our case. Multi-character constant is not considered as a good programming practiced and should be ignored.

## String literals

String literal is a sequence of characters enclosed within double quotes. String constant occupies (total count of characters + 1) byte space in memory. The additional 1 byte is used for `\0`

(NULL) character. A `NULL`

value is added explicitly at the end of the string to specify termination of the string. You can also concatenate string literals using `+`

operator.

Examples of some valid string constants

`"I love programming!"`

`I love Codeforwin.\n" + "I love India.`

**Important note:** `'A'` and `"A"` both looks similar but in real both are different. `'A'` is a character constant occupying 1 byte space in memory. Whereas `"A"` is a string constant and occupies 2 byte space in memory.

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