What is constant? Write down briefly about different type of constant?


Constants are of fixed values that do not change during the execution of a program. There are various types of constants. The types are illustrated in the following figure.


Integer constants: 

An integer constant refers to a sequence of digits. There are three types of integer constants, namely, decimal integer, octal integer and hexadecimal integer.

Decimal integer consists of a set of digits from 0 to 9, preceded by an optional + or – sign. 

Examples,      123     -321    0          64932

Octal integer consists of a set of digits from 0 to 7, with a leading 0. 

Examples, 037     0      0437         0551

Hexadecimal integers are a sequence of digits preceded by 0x or 0X. They may also includes letters from A to F or from a to f. The letters represents the numbers from 10 to 15.Examples,            0X2     0x9F   0Xbcd    0x

Real constants:

Real constants are used to represent quantities that are very continuously, such as distances, temperature etc. These quantities are represented by numbers containing fractional parts. Examples,      0.00832          -0.75               33.337

Single character constants:

A single character constants contains a single character enclosed within a pair of single quote marks. Example, ‘5’         ‘X’       ‘;’

String constants:

A string constant contains a string of characters enclosed within a pair of double quote marks. Examples,    “Hello !”         “1987”            “?....!”

Backslash character constants:

C supports some special backslash character constants that are used in output functions. For example

                  Constants                                                    Meaning
                        ‘\a’                                                       audible alert (bell)
                        ‘\n’                                                      new line

                        ‘\?’                                                       question mark

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