Question about Lexx & Yacc

[Nattapong]

Hello there!,

I hope I send my question to the right place. If not, I apologize for that.

The question is about my simple program on Lex & Yac ... (well actually 
flex and yacc).

please take a look at my "ch1-05.y". I compiled the code without any 
problem. But
the error hit me when I tried to run it. "Segmentation Fault"

Listing === ch1-05.y
------------------------------------------------------------------
%{
#include <stdio.h>
%}

%token NOUN PRON VERB ADV ADJ PREP CONJ

%%

sentence: subject VERB object { printf ("Sentence is valid.\n"); }
  ;

subject:     NOUN
      |    PRON
      ;
object:        NOUN
      ;
%%

extern FILE *yyin;

main ()
{
  while (!feof(yyin)) {
          yyparse ();
  }
}

yyerror (s)
char *s;
{
  fprintf (stderr, "%s\n", s);
}
------------------------------------------------------------------

The program terminated when it hit "feof ()".
This problem only occur when running on linux but not solaris.
I guess that is because the lex and yacc program on the two systems are 
different.

Below is my lex file "ch1-05.l"
------------------------------------------------------------------
%{
/*
* Word recognizer with a symbol table
*/

#include "y.tab.h"

#define LOOKUP 0

int state;

int add_word (int type, char *word);
int lookup_word (char *word);

%}

%%
\n { state = LOOKUP; }

\.\n { state = LOOKUP;
return 0;
}

^verb { state = VERB; }
^adj { state = ADJ; }
^adv { state = ADV; }
^noun { state = NOUN; }
^prep { state = PREP; }
^pron { state = PRON; }
^conj { state = CONJ; }

[a-zA-Z]+ {
  if (state != LOOKUP) {
      add_word (state, yytext);
  }
  else {
      switch (lookup_word (yytext)) {
          case VERB:
              return (VERB);
          case ADJ:
              return (ADJ);
          case ADV:
              return (ADV);
          case NOUN:
              return (NOUN);
          case PREP:
              return (PREP);
          case PRON:
              return (PRON);
          case CONJ:
              return (CONJ);

          default:
              printf ("%s: don't recognize\n", yytext);
      }
  }
}

.     ;

%%
struct word {
  char *word_name;
  int word_type;
 };

struct word *word_list; /* first element in word list */

extern void *malloc();

int add_word (int type, char *word)
{
struct word *wp;

if (lookup_word (word) != LOOKUP) {
printf ("!!! warning: word %s already defined \n", word);
return 0;
}

/* word not there, allocate a new entry and link it on the list */

wp = (struct word *) malloc (sizeof (struct word));

wp->next = word_list;

/* have to copy the word itself as well */

wp->word_name = (char *) malloc (strlen (word) + 1);
strcpy (wp->word_name, word);
wp->word_type = type;
word_list = wp;
return 1; /* it worked! */

}

int lookup_word (char *word)
{
struct word *next;
struct word *wp = word_list;

for (;wp;wp = wp->next) {
if (strcmp (word, wp->word_name) == 0) {
return wp->word_type;
}
}

return LOOKUP; /* word not found */
}

--------------------------------------------------------------------