Bison:syntax error at the end of parsing -

hello bison grammar file mini-programming language:

    %{  #include <stdlib.h>  #include <stdio.h>  #include <math.h>  #include "projectbison.tab.h"   void yyerror(char const *);    extern file *yyin;  extern file *yyout;   extern int yylval;  extern int yyparse(void);  extern int n;  int errnum = 0;  int fornum = 0; %}  %left plus minus %left mult div mod %nonassoc equal nequal less greater lequal gequal   %token integer boolean string void  %token id %token ,  %token beginp  %token endp %token extern  %token comma %token eq %token return1 %token if1 else1 while1 for1 do1  %token lor land lnot %token true false %token equal nequal less greater lequal gequal %token lb1 rb1              %token lcb1 rcb1 %token semic %token newline %token plus minus  %token mult div mod %token digit string1 %start program  %%   /*50*/ program : external-decl program-header defin-field command-field          ; external-decl : external-decl external-prototype                |                ; external-prototype : extern prototype-func newline                                 ; program-header : void id lb1 rb1 newline                    ; defin-field : defin-field definition              |               ; definition : variable-defin            | func-defin            | prototype-func            ; variable-defin : data-type var-list semic newline                ; data-type : integer                          | boolean           | string           ; var-list : id extra-ids           ; extra-ids : comma var-list       |        ; func-defin : func-header defin-field  command-field             ; prototype-func : func-header semic                   ; func-header : data-type id lb1 lists rb1 newline              ; lists: list-typ-param     |      ; list-typ-param : typical-param typical-params               ; typical-params : comma list-typ-param           |          ; typical-param : data-type , id         ; command-field : beginp  commands newline endp newline     ; commands : commands newline command      |      ; command : simple-command semic          | struct-command         | complex-command         ; complex-command : lcb1 newline command newline rcb1                   ; struct-command  : if-command                 | while-command                 | for-command                 ; simple-command : assign               | func-call               | return-command               | null-command               ; if-command : if1 lb1 gen-expr rb1 newline command else-clause           ; else-clause: else1 newline command                ; while-command : while1 lb1 gen-expr rb1 do1 newline rcb1 command lcb1                ; for-command : for1 lb1 conditions rb1 newline rcb1 command lcb1               ; conditions : condition semic condition semic condition semic        ; condition : gen-expr       |        ; assign : id eq gen-expr           ; func-call  : id lb1 real-params-list rb1           | id lb1 rb1           ; real-params-list : real-param real-params                  ; real-params : comma real-param real-params          |          ; real-param : gen-expr          ; return-command : return1 gen-expr               ; null-command :              ; gen-expr : gen-terms gen-term          ; gen-terms : gen-expr lor           |            ;  gen-term : gen-factors gen-factor          ; gen-factors : gen-term land           |          ; gen-factor : lnot first-gen-factor                 |  first-gen-factor                  ; first-gen-factor : simple-expr comparison                  | simple-expr                  ; comparison : compare-operator simple-expr             ; compare-operator : equal                           | nequal                  | less                  | greater                  | lequal                  | gequal                  ; simple-expr : expresion simple-term     ; expresion : simple-expr plus         |simple-expr minus     |      ; simple-term : mul-expr simple-parag             ; mul-expr: simple-term mult     | simple-term div     | simple-term mod     |      ; simple-parag : simple-prot-oros              | minus simple-prot-oros              ; simple-prot-oros : id                  | constant                  | func-call                  | lb1 gen-expr rb1                  ; constant : digit          | string1          | true          | false          ; newline:newline     |      ;    %%  void yyerror(char const *msg)  { errnum++; fprintf(stderr, "%s\n", msg);  } int main(int argc, char **argv)  { ++argv; --argc; if ( argc > 0 )  {yyin= fopen( argv[0], "r" ); } else  {yyin = stdin;   yyout = fopen ( "output", "w" );}  int = yyparse(); if(a==0) {printf("done parsing\n");} else {printf("yparxei lathos sti grammi: %d\n", n);}  printf("estimated number of errors: %d\n", errnum);  return 0; } 

for simple input :

void main() integer k; boolean l; begin aek=32; end 

i following :

$ ./myparser.exe file2.txt void , id ,left bracket , right bracket integer , id ,semicolon boolean , id ,semicolon begin program id ,equals , digit ,semicolon end program syntax error yparxei lathos sti grammi: 8 estimated number of errors: 1 

and whatever change make input file syntax error @ end....why , can do??thanks lot in advance!here flex file in case needs :

%{ #include "projectbison.tab.h" #include <stdio.h> #include <stdlib.h> #include <string.h>  int n=1; %} %option noyywrap   digit   [0-9]+ id      [a-za-z][a-za-z0-9]*    %%  "(" {printf("left bracket , "); return lb1;} ")" {printf("right bracket\n"); return rb1;} "{" {printf("left curly bracket , "); return lcb1;} "}" {printf("right curly bracket\n"); return rcb1;} "==" {printf("isotita ,"); return equal;} "!=" {printf("diafora ,"); return nequal;} "<" {printf("less_than ,"); return less;} ">" {printf("greater_than ,"); return greater;} "<=" {printf("less_eq ,"); return lequal;} ">=" {printf("greater_eq ,"); return gequal;} "||" {printf("lor\n"); return lor;} "&&" {printf("land\n"); return land;} "&" {printf("and ,"); return and;} "!" {printf("lnot ,"); return lnot;} "+" {printf("plus ,"); return plus; } "-" {printf("minus ,"); return minus;} "*" {printf("multiply ,"); return mult;} "/" {printf("division ,"); return div;} "%" {printf("mod ,"); return mod;} ";" {printf("semicolon \n"); return semic;} "=" {printf("equals , "); return eq;} "," {printf("comma ,"); return comma;} "\n" {n++; return newline;} void {printf("void ,"); return void;} return {printf("return ,"); return return1;} extern {printf("extern\n"); return extern;} integer {printf("integer ,"); return integer;} boolean {printf("boolean ,"); return boolean;} string {printf("string ,"); return string;} begin {printf("begin program\n"); return beginp;} end {printf("end program\n"); return endp;} {printf("for\n"); return for1;} true {printf("true ,"); return true;} false {printf("false ,"); return false;} if {printf("if\n"); return if1; } else {printf("else\n"); return else1; } while {printf("while\n"); return while1;} {id} {printf("id ,"); return id;} {digit}  {printf("digit ,"); return digit;} [a-za-z0-9]+  {return string1;} ` {/*catchcall*/ printf("mystery character %s\n", yytext); } <<eof>> { static int once = 0; return once++ ? 0 : '\n'; }  %% 

your scanner pretty guarantees 2 newline characters sent @ end of input: 1 newline present in input, , 1 result of trapping <<eof>>. however, grammar doesn't appear accept unexpected newlines, second newline trigger syntax error.

the simplest solution remove <<eof>> rule, since text files without terminating newline rare, , entirely legitimate consider them syntax errors. more general solution allow number of newline characters appear newline expected, defining like:

newlines: '\n' | newlines '\n'; 

(using actual characters single-character tokens makes grammar much more readable, , simplifies scanner. that's side issue.)

you might ask whether need enforce newline terminators, since grammar seems use ; statement terminator, making newline redundant (aside stylistic considerations). removing newlines grammar (and ignoring them, other whitespace, in scanner) simplify code.