In C Programming Language constant is an entity with a fixed value, and this value does not change throughout the execution of the program. C constants are also known as ‘Literals’. There are four basic types of constants in C Programming Language.

Integer Constants

An integer constant can only hold integer quantity which is a sequence of whole numbers or digits.

• Integer constant can not have a decimal point or fractional part.
• Blanks and commas are not allowed within an integer constant.
• An integer constant can be either +ve or -ve.
• The constant must lie within the range of the declared data type (including qualifiers long, short, etc.).

An integer constant can be either Decimal, Hexa Decimal, or Octal.
A decimal integer constant consists of any combination of digits taken from the set 0 through 9. If the decimal constant contains two or more digits, the first digit can not be 0 (Zero).

Example:

12, 15, 456 etc.

An octal integer constant is a combination of digits taken from the set 0 through 7. In octal representation, the first digit must be a 0(Zero), in order to identify the constant as an octal number.

Example:

0, 05, 054

A hexadecimal integer constant must begin with either 0x or 0X. It can then be followed by any combination of digits taken from the set 0 through 9 and alphabets from A to F (either upper-case or lower-case are valid).

Example:

0x65F, 0X7A

Floating Point Constants

A floating-point or real constant contains a decimal point or an exponent.

• A real constant must have at least one digit each to the left and right of the decimal point.
• It can be either +ve or -ve.
• Commas and blank space are not allowed within a real constant.

A real constant can be represented in two forms: Factorial form or Exponential form.

A real constant in a fractional form must have at least one digit each to the left and right of the decimal point.

Example:

15.75, -2.25

A floating-point in exponent form consists of a mantissa and an exponent.

Example:

-2.5e-3, 25E-4

Character Constants

A character constant is a single character, enclosed in single quotation marks. It can be a single alphabet, a digit, or a special symbol. The maximum length of a character constant is one character.

Example:

‘A’, ‘5’, ‘$’

String Constants

A string constant is a sequence of characters enclosed in double quotes. It may contain letters, digits, special characters, and blank spaces.

Example:

“HELLO”, “world”