In C language, a constant is similar to the variable but constant holds only one value at the time of program execution. That means, once a value is taken to the constant, than it can’t be changed during the program execution time. Once the value is assigned to the constant, it is fixed throughout the program. Therefore a constant can be defined as, it is a named memory location that can holds only one value throughout the execution of program.
In C programmig language, constant can be of any data type like integer, floating point, character, string and double etc.,
constant can be a decimal integer or octal integer or hexa decimal integer. A
decimal integer value is specified as direct integer value whereas octal
integer value is prefixed with ‘o’ and hexa decimal value is prefixed with
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’.
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. Sometimes it may also contain exponent part. When a floating point constant is represented in exponential form, the value must be end with ‘e’ or ‘E’.
The floating point value 3.14 is represented as 3E-14 in exponent form.
*A character constant is a symbol.
* A character symbol is enclosed in single quotation.
* A character constant has a maximum length of one character.
Examples:- ‘A’, ‘2’, ‘+’ , ‘z’ etc.
In C programming language, there are some predefined character constants called escape sequences. Every escape sequence has its own special functionality and every escape sequence is prefixed with ‘\’ symbol. These escape sequences are used in output function that is called ‘printf()’.
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…
“This is bcaguru”
We can define string constant using multiple lines as follows…
We can also define string constant by separating it with white space as follows…
“This” “is” “bcaguru”
All the above three defines the same string constant.
Creating constants in C
In c programming language, constants can be created using two concepts…
- Using ‘const’ keyword
- Using ‘#define’ preprocessor
1)Using ‘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 ;
const datatype constantName = value ;
const int x = 10 ;
Here, ‘x’ is a integer constant with fixed value 10.
int i = 9 ;
const int x = 10 ;
i = 15 ;
x = 100 ; // creates an error
printf(“i = %d\nx = %d”, i, x ) ;
The above program gives an error because we are trying to change the constant variable value (x = 100).
Using ‘#define’ preprocessor
We can also
create constants using ‘#define’ preprocessor directive. When we create
constant using this preprocessor directive it must be defined at the beginning
of the program (because all the preprocessor directives must be written before
the gloabal declaration).
We use the following syntax to create constant using ‘#define’ preprocessor directive…
#define CONSTANTNAME value
#define PI 3.14
Here, PI is a constant with value 3.14.
#defien PI 3.14
int r, area ;
printf(“enter the radius of circle :- “) ;
scanf(“%d”, &r) ;
area = PI * (r * r) ;
printf(“Area of the circle = %d”, area) ;