#include <stdio.h>

// this is the old-school way to define constants
#define LINELEN 128

double sphere_volume(double radius);
{
  double volume;

  // this is the new way to define constants
  const float PI = 3.141592653;

  volume = 4.0 / 3.0 * PI * radius^2;
  return volume;
}

int main()
{
  double radius;
  char line[LINELEN];
  double volume;

  // prompt the user and get input
  printf("Enter the radius of the sphere in meters:\n");
  fgets(line, LINELEN, stdin);
  sscanf(line, "%f\n", radius);

  // compute the volume and print the result
  volume = sphere_volume(double radius);
  printf("The volume of a sphere with radius %f m is %f m^3\n", 
	 radius, volume);
}