Linked list error

typedef struct node {
int num;
struct node *next;
}message;
int main ()
{
   FILE *file;
   char array[5];
   message *temp *head, *ptr, *previous;
   head = 0;  
 
   if ((file=fopen(argv[1],"r")) == NULL)
   printf("nofile\n");

   while (fgets(array, sizeof(array),file)!= NULL)
   {
      temp = malloc (sizeof(struct node));
      temp -> num = atoi(array);
         
      previous = 0;

      while ((ptr != 0) && ( (atoi(array)) > (ptr -> num)))
      {
          previous = ptr;
          ptr = ptr -> next;
      }

      temp -> next = ptr;

      if (previous != 0 )
          previous -> next = temp;
      else
          head = temp;

      /*im not so sure of how to not add the same value. For example, if num = a previous node,
         it wouldn't append that num to the list. */

      }
   return 0;
}