C Constants

Constants are like a variable, except that their value never changes during execution once defined.

C Constants is a most fundamental and essential part of C programming language. Constants in C are the fixed values that are used in a program, and its value remains the same during the entire execution of the program.

  • Constants are also called literals.
  • Constants can be any of the data types.
  • It is considered best practice to define constants using only upper-case names.

Constant Definition in C

const type constant_name;

const keyword defines a constant in C.

  const int SIDE = 10;
  int area;
  area = SIDE*SIDE;
  printf("The area of the square with side: %d is: %d sq. units"
  , SIDE, area);
Program Output:


Putting const either before or after the type is possible.

int const SIDE = 10;


const int SIDE = 10;

Constant Types in C

Constants are categorized into two basic types, and each of these types has own subtypes/categories. These are:

Primary Constants
  1. Numeric Constants
    • Integer Constants
    • Real Constants
  2. Character Constants
    • Single Character Constants
    • String Constants
    • Backslash Character Constants

Integer Constant

It's referring to a sequence of digits. Integers are of three types viz:

  1. Decimal Integer
  2. Octal Integer
  3. Hexadecimal Integer

15, -265, 0, 99818, +25, 045, 0X6

Real constant

The numbers containing fractional parts like 99.25 are called real or floating points constant.

Single Character Constants

It simply contains a single character enclosed within ' and ' (a pair of single quote). It is to be noted that the character '8' is not the same as 8. Character constants have a specific set of integer values known as ASCII values (American Standard Code for Information Interchange).


'X', '5', ';'

String Constants

These are a sequence of characters enclosed in double quotes, and they may include letters, digits, special characters, and blank spaces. It is again to be noted that "G" and 'G' are different - because "G" represents a string as it is enclosed within a pair of double quotes whereas 'G' represents a single character.


"Hello!", "2015", "2+1"

Backslash character constant

C supports some character constants having a backslash in front of it. The lists of backslash characters have a specific meaning which is known to the compiler. They are also termed as "Escape Sequence".

For Example:

\t is used to give a tab

\n is used to give a new line

\abeep sound
\fform feed
\nnew line
\rcarriage return
\thorizontal tab
\vvertical tab
\'single quote
\"double quote
Secondary Constant

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