Constants in C Programing with Example

 Constants:

A constant is analogous to the variable but the constant hold just one value during the program execution. In constant once a value is assigned to the constant, that value cannot be changed during the program execution. Once value is assigned to the constant, it is fixed throughout the program.

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

Creating constants in C

Constant  can be created using two concepts.

Using the 'const' keyword-

We create a constant of any data type using 'const' keyword. To create a constant , we prefix the variable declaration with 'const' keyword.

Syntax

const datatype constantName;

                    or 

const datatype constantName=value;

Example:

const int c=10;

Here 'x' is a integer constant with fixed value 10.

 

Q.N. write code for const and try to change value of contant and show error.

code_

#include<stdio.h>

#include<conio.h>

void main()

{

int i=9;

const int x=10;

i=15;

x=100; // give an error

printf("i=%d\nx=%d",i,x);

getch();

}

ouput: Error (constant value cannot be changed)

Using "#define" preprocessor-

We can also create constants using "#define" preprocessor directive. When  create a 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 global declaration).

Syntax:

#define CONSTANTNAME value

Q.N. find area of circle using constant function definition

#define PI 3.14;

Here ,PI is a constant with value 3.14;

Program:

#include<stdio.h>

#include<conio.h>

#define PI 3.14

void main()

{

int r; 

float area;

printf("Enter the radius of circle:");

scanf("%d",&r);

area= PI*r*r;

printf("Area of the circle=%f",area);

}

output:

Enter the radius of circle:5

Area of the circle=78.500000

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