#include <stdio.h>

void help(void) {
   fprintf(stdout,"usage: xfpp3d [-h] [-c]\n");
   fprintf(stdout,"\n");
   fprintf(stdout,"Displays animations of three dimensional particle motion.\n");
   fprintf(stdout,"\n");
   fprintf(stdout,"   Options: -h   Displays this help message.\n");
   fprintf(stdout,"            -c   Enables user-specified coloring (RGB) of particles.\n");
   fprintf(stdout,"\n");
   fprintf(stdout,"xfpp3d reads ASCII input from standard input in one of the following\n");
   fprintf(stdout,"two formats:\n");
   fprintf(stdout,"\n");
   fprintf(stdout,"FORMAT 1: Default (all particles displayed in single, fixed color)\n");
   fprintf(stdout,"\n");
   fprintf(stdout,"       <np>                            ! Number of particles\n");
   fprintf(stdout,"       <size_1>                        ! Relative display size of particle 1\n");
   fprintf(stdout,"       <size_2>                        ! Relative display size of particle 2\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"       <size_np>                       ! Relative display size of particle np\n");
   fprintf(stdout,"       <t_1>                           ! First display time\n");
   fprintf(stdout,"       <x_1_1>  <y_1_1>  <z_1_1>       ! Coordinates of particle 1 at t_1\n");
   fprintf(stdout,"       <x_1_2>  <y_1_2>  <z_1_2>       ! Coordinates of particle 2 at t_1\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"       <x_1_np> <y_1_np> <z_1_np>      ! Coordinates of particle np at t_1\n");
   fprintf(stdout,"       <t_2>                           ! Second display time\n");
   fprintf(stdout,"       <x_2_1>  <y_2_1>  <z_2_1>       ! Coordinates of particle 1 at t_2\n");
   fprintf(stdout,"       <x_2_2>  <y_2_2>  <z_2_2>       ! Coordinates of particle 2 at t_2\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"       <x_2_np> <y_2_np> <z_2_np>      ! Coordinates of particle np at t_2\n");
   fprintf(stdout,"       <t_3>                           ! Third display time\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"\n");
   fprintf(stdout,"  All values are expected to be real numbers except for <np> which is\n");
   fprintf(stdout,"  an integer.\n");
   fprintf(stdout,"\n");
   fprintf(stdout,"FORMAT 2: User-specified coloring (enabled via -c option).  Colors are specfied \n");
   fprintf(stdout,"          as RGB (red-green-blue) triples, where each color component is a \n");
   fprintf(stdout,"          real number between 0.0 and 1.0.\n");
   fprintf(stdout,"\n");
   fprintf(stdout,"       <np>                            ! Number of particles\n");
   fprintf(stdout,"       <size_1> <R_1> <G_1> <B_1>      ! Relative size and color of part. 1\n");
   fprintf(stdout,"       <size_2> <R_2> <G_2> <B_2>      ! Relative size and color of part. 2\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"       <size_np> <R_np> <G_np> <B_np>  ! Relative size and color of part. np\n");
   fprintf(stdout,"       <t_1>                           ! First display time\n");
   fprintf(stdout,"       <x_1_1>  <y_1_1>  <z_1_1>       ! Coordinates of particle 1 at t_1\n");
   fprintf(stdout,"       <x_1_2>  <y_1_2>  <z_1_2>       ! Coordinates of particle 2 at t_1\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"       <x_1_np> <y_1_np> <z_1_np>      ! Coordinates of particle np at t_1\n");
   fprintf(stdout,"       <t_2>                           ! Second display time\n");
   fprintf(stdout,"       <x_2_1>  <y_2_1>  <z_2_1>       ! Coordinates of particle 1 at t_2\n");
   fprintf(stdout,"       <x_2_2>  <y_2_2>  <z_2_2>       ! Coordinates of particle 2 at t_2\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"       <x_2_np> <y_2_np> <z_2_np>      ! Coordinates of particle np at t_2\n");
   fprintf(stdout,"       <t_3>                           ! Third display time\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"                   .\n");
   fprintf(stdout,"  All values are expected to be real numbers except for <np> which is\n");
   fprintf(stdout,"  an integer.\n");
   exit(1);
}