kisukedeath on "Problem developing plugin"

Hi I have this problem :( :

How I can validate when you have five posts with the same tag automatically generate a custom_post_type with the name of the tag and this custom_post_type act as a tag page?

I am developing a plugin but I can not create the dynamically custom_post_type, this is my code. I test it calling this in my index.php <?php cus_post(); ?>, but just got validate if(countRepeat($tags_arr[$i],$tags_arr)== 5) and can´t create the custom_post_type (register_post_type). I notice that when I write just this :function cus_post(){

register_post_type('prueba',
          array(
         'labels' => array(
            'name' => __($tags_arr[0]),
            'singular_name' => __($tags_arr[0])
         ),
         'public' => true,
         'has_archive' => true,
      )
   );
}

is created.

<?php
   /*
      Plugin Name: Plugin-test.
      Plugin URI: Url del plugin.
      Description:  Descripcion.
      Version: Numero de versiones 1,2,..10.
      Author: Nombre del autor.
      Author URI: Pagina personal del autor.
   */

function cus_post(){

 while(have_posts()) : the_post();
   $posttags = get_the_tags();
   if($posttags){
      foreach($posttags as $tag){
         $tags_arr[] = $tag -> name;
      }
   }
endwhile;

for ($i=0; $i < sizeof($tags_arr) ; $i++) { 

   if(countRepeat($tags_arr[$i],$tags_arr)== 5){
          register_post_type('prueba',
          array(
         'labels' => array(
            'name' => __($tags_arr[0]),
            'singular_name' => __($tags_arr[0])
         ),
         'public' => true,
         'has_archive' => true,
      )
   );
      }

function countRepeat($value, array $array){
$count = 0;
   foreach($array as $k => $v)
   {
      if((string)$v == (string)$value)
      {
         ++$count;
      }
   }
   return $count;
}
   }

add_action('init','cus_post');

?>