C Constants

 A constant is similar to the variable but the constant hold only one value during the program execution.That means, once a value is assigned to the constant, that value can't be changed during the program execution. Once the value is assigned to the constant, it is fixed throughout the program.

In C programming language, a constant can be of any data type like integer, floating-point, character, string and double, etc. 

Integer constants

An integer constant can be a decimal integer or octal integer or hexadecimal integer. A decimal integer value is specified as direct integer value whereas octal integer value is prefixed with 'o' and hexadecimal value is prefixed with 'OX'.
An integer constant can also be unsigned type of integer constant or long type of integer constant. Unsigned integer constant value is suffixed with 'u' and long integer constant value is suffixed with 'l' whereas unsigned long integer constant value is suffixed with 'ul'.

Example

125 -----> Decimal Integer Constant
O76 -----> Octal Integer Constant
OX3A -----> Hexa Decimal Integer Constant
50u -----> Unsigned Integer Constant
30l -----> Long Integer Constant
100ul -----> Unsigned Long Integer Constant

Floating Point constants

A floating-point constant must contain both integer and decimal parts. Some times it may also contain the exponent part. When a floating-point constant is represented in exponent form, the value must be suffixed with 'e' or 'E'.

Example

The floating-point value 3.14 is represented as 3E-14 in exponent form.

Character Constants

A character constant is a symbol enclosed in single quotation. A character constant has a maximum length of one character.

Example

'A'    , '2' 

 

String Constants

 

A string constant is a collection of characters, digits, special symbols and escape sequences that are enclosed in double quotations.

We define string constant in a single line as follows...

 "Hello Everyone"

Creating constants in C

In a c programming language, constants can be created using two concepts... 

• Using the 'const' keyword
• Using '#define' preprocessor

Using the 'const' keyword

We create a constant of any datatype using 'const' keyword. To create a constant, we prefix the variable declaration with 'const' keyword.
The general syntax for creating constant using 'const' keyword is as follows...

const datatype constantName ;

or

const datatype constantName = value ;

 

Example

#include<stdio.h>
#include<conio.h>
void main(){

   int i = 5 ;
   const int j = 100 ;
      
   i = 50 ;
   j = 200 ;
   printf("i = %d\nj = %d", i, j ) ;
  getch();
}

Output 

 The above program gives an error because we are trying to change the constant variable value (j = 200).

 

Using '#define' preprocessor

The #define preprocessor directive is used to define constant or micro substitution. It can use any basic data type.

We use the following syntax to create constant using '#define' preprocessor directive...

#define CONSTANTNAME value

 

Example

     #include <stdio.h>
    #include<conio.h>
    #define PI 3.14  
    main() {  
       printf("%f",PI);
       getch();
    }  

Output