Why do I get a syntax error in my program made with flex and yacc? - grammar

Question

I made a program that is supposed to recognize a simple grammar. When I input what I think is supposed to be a valid statement, I get an error. Specifically, if I type
int a;
int b;
it doesn't work. After I type int a; the program echoes ; for some reason. Then when I type int b; I get syntax error.
The lex file:
%{
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#include "y.tab.h"
%}
else ELSE
if IF
int INT|int
return RETURN
void VOID
while WHILE
id [a-zA-Z]*
num [0-9]*
lte <=
gte >=
equal ==
notequal !=
%%
{else} { return ELSE; }
{if} { return IF; }
{int} { return INT; }
{return} { return RETURN; }
{void} { return VOID; }
{while} { return WHILE; }
{id} { return ID; }
{num} { return NUM; }
{lte} { return LTE; }
{gte} { return GTE; }
{equal} { return EQUAL; }
{notequal} { return NOTEQUAL; }
%%
The yacc file:
/* C-Minus BNF Grammar */
%token ELSE
%token IF
%token INT
%token RETURN
%token VOID
%token WHILE
%token ID
%token NUM
%token LTE
%token GTE
%token EQUAL
%token NOTEQUAL
%%
program : declaration_list ;
declaration_list : declaration_list declaration | declaration ;
declaration : var_declaration | fun_declaration ;
var_declaration : type_specifier ID ';'
| type_specifier ID '[' NUM ']' ';' ;
type_specifier : INT | VOID ;
fun_declaration : type_specifier ID '(' params ')' compound_stmt ;
params : param_list | VOID ;
param_list : param_list ',' param
| param ;
param : type_specifier ID | type_specifier ID '[' ']' ;
compound_stmt : '{' local_declarations statement_list '}' ;
local_declarations : local_declarations var_declaration
| /* empty */ ;
statement_list : statement_list statement
| /* empty */ ;
statement : expression_stmt
| compound_stmt
| selection_stmt
| iteration_stmt
| return_stmt ;
expression_stmt : expression ';'
| ';' ;
selection_stmt : IF '(' expression ')' statement
| IF '(' expression ')' statement ELSE statement ;
iteration_stmt : WHILE '(' expression ')' statement ;
return_stmt : RETURN ';' | RETURN expression ';' ;
expression : var '=' expression | simple_expression ;
var : ID | ID '[' expression ']' ;
simple_expression : additive_expression relop additive_expression
| additive_expression ;
relop : LTE | '<' | '>' | GTE | EQUAL | NOTEQUAL ;
additive_expression : additive_expression addop term | term ;
addop : '+' | '-' ;
term : term mulop factor | factor ;
mulop : '*' | '/' ;
factor : '(' expression ')' | var | call | NUM ;
call : ID '(' args ')' ;
args : arg_list | /* empty */ ;
arg_list : arg_list ',' expression | expression ;

Answer 1

Ok...you need to add a semi-colon as a token as well in your language spec...as a fyi, do a google search on this ...there are a few lex/yacc files for C programming language as well...and there are plenty of tutorials on this...flex/bison are not exactly forgiving on program spec errors...you really need to understand the elements of how it works...Look for Jack Crenshaw's famous tutorial on how to build a compiler.

Answer 2

Lex:
id [a-zA-Z]*
num [0-9]*
both cases can meet empty strings, use '+' instead