/* 
  Program: define.c

  Using #define directives to define constants.

*/

#include <stdio.h>
#include "genlib.h"
#include "simpio.h"

#define PI 3.14159

main() {
    double radius, area;

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

    area = radius * radius * PI ;
    printf("The area of a circle with radius %g is %g\n",
       radius, area) ;
}

----------------------------------------------------------- 

lassie% cc201 define.c
lassie% 

lassie% a.out
Enter the radius of the circle: 17.23
The area of a circle with radius 17.23 is 932.653
lassie%