/******* Problem 4--Clock Angles **************************************
 One important fact about these programming contests is that the
 problems are not ordered by difficulty.  Before the contest, they
 announced that one of the problems was essentially a "Hello World"
 problem, meaning that it was easy.  This was that problem.  Most teams
 were able to get this one.  The computation was straightforward.
 **********************************************************************/

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

int main (int argc, char **argv);
static double angle (int h, int m);

FILE *in, *out;

/******* main *********************************************************
 The program reads a series of hour-minute pairs from the input file
 and prints the angle between the clock hands correct to the nearest
 tenth of a degree.
 *********************************************************************/

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

  int h, m;   /* The hour-minute pair */

 in = fopen ("prob4.in","r");   /* redirecting input and output */
 out = fopen ("prob4.out","w");
 while (1) {               /* read in hour-minute pairs and print out */
  fscanf (in,"%d %d",&h,&m); /* the angle between them until hour and */
  if (h==0 && m==0) break; /* minute are both 0. */
  fprintf (out,"At %d:%02d the angle is %.1f degrees.\n",h,m,
           angle(h,m));
 }
 fclose (in);    /* closing the files */
 fclose (out);
 return EXIT_SUCCESS;
}

/******** angle *******************************************************
 angle accepts two integers, the hour and minute, and returns a double
 containing the angle between the two hands of the clock.  The angle
 must be between 0 and 180 degrees.
 **********************************************************************/

static double angle (int h, int m) {

  double ha, ma,   /* The angle of the hour and minute hands */
         a;        /* The angle (to be returned) between the hands */

 ma = m * 6;   /* The difference between minutes is 6 degrees each */
 ha = (h%12) * 30 + ma/12;  /* The difference between hours is 30
                               degrees each, plus each time the minute
                               hand is advanced, the hour hand is 
                               advanced by one-twelfth as much. */
 a = fabs (ma-ha);  /* The distance between the hands in degrees */
 return a > 180 ? 360-a : a;  /* Making sure we return the smaller angle
                                 between the hands */
}