Study of #define macros.

#include <stdio.h>

/* Creating simple macros */
#define PI 3.14
#define MESSAGE "\nEnter radius : "

int main(void)
{
float r, circum;

printf(MESSAGE);
scanf("%f", &r);

circum = 2 * PI * r;

printf("\nCircumference of circle with radius %f is %f", r, circum);

return 0;
}