#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>

int main (int argc, char **argv) {

  double n;

 printf ("Enter a number:  ");
 scanf ("%lf",&n);  //reads in n
 if (n >= 0)
  printf ("The square root of %f is %f.\n",n,sqrt(n));
 else
  fprintf (stderr,"Can't print the square root of a negative number, ding dong.\n");
 return 0;
}