WAP to Use of const keyword

/*WAP to Use of const keyword */

#include<stdio.h>
#include<conio.h>
main( )
{
 float r, a ;
 const float pi = 3.14 ;

 printf ( "\nEnter radius of circle " ) ;
 scanf  ( "%f", &r ) ;
 a = pi * r * r ;
 printf ( "\nArea of circle = %f", a ) ;
}