Syntax error in lex & yacc file

Question

I am pretty new to lex and yacc. I was trying out a grammar to recognize the input text: ESCREVER 1; or ESCREVER 1+2; but everytime I try it shows me syntax error , I think the problem is parsing the number or the word ESCREVER.

Here is my flex/lex code

%{
#include "gram.h"

int yyerror(const char *s);

%}



/* letras [A-Za-z]+ */


/* id     ({letras})({letras}|{digito})* */

%%

"ESCREVER" {return   ESCREVER; }                                
"TERMINAR" {return TERMINAR; }

[0-9]+     { yylval.num =atoi(yytext);
             return NUM; }


[A-Za-z0-9]* { yylval.str=strdup(yytext);
                return TEXTO;}


"/" | 
"-" |
"+" |
"*" |
"=" |
.          {return yytext[0];}
[ \n\t]    {  }


%%


int yywrap(){ return 1; }

YACC code:

%{

  #include <stdio.h>
  int yylex(void);
  int yyerror(const char *s);


%}
%union{
        char *str; /* para strings*/
        int num; /* para inteiros */
     }

%token TERMINAR ESCREVER
%token SUBTRACAO 
%token MULTIPLICACAO 
%token DIVISAO 
%token SOMA
%token<num> NUM /*para inteiros*/
%token<str> TEXTO /*MUDAR PARA VAR*/
%type<num> elemento
%type<num> expr 
%type<num> lista
%start s

%%

s:linha s
 |TERMINAR ';' {return 0;}
 ;

linha: ESCREVER lista';' {printf("%d",$2);}                       
     | VARS
     ;

lista: lista ',' elemento
     | elemento
     ;

elemento:NUM
        |expr
        ;





VARS :
     | NUM 
     | TEXTO
     | expr
     | TEXTO '=' VARS ';' /* para delcaracoes */
     ;



expr     : NUM  SOMA expr                {$$=$1+$3;}
         | NUM  SUBTRACAO expr           {$$=$1-$3;}
         | NUM  MULTIPLICACAO expr       {$$=$1*$3;}
         | NUM  DIVISAO expr             {$$=$1/$3;}
     | NUM  '+' expr                 {$$=$1+$3;}
         | NUM  '=' expr                 {$$=$1=$3;}
         | NUM  '-' expr                  {$$=$1-$3;}
         | NUM  '*' expr                 {$$=$1*$3;}
         | NUM  '/' expr                  {$$=$1/$3;}
         | NUM                           {$$=$1;   }
         ;             


%%


int yyerror(char const *s) {
    fprintf(stderr,"Erro: %s\n",s); 
    return 0;
}

int main(int argc, char *argv[]) {
    extern FILE *yyin;

    if (argc > 1) {
        if((yyin=fopen(argv[1],"r"))==NULL){
            fprintf(stderr,"erro ao abrir o ficheiro \"%s\".\n",argv[1]);
            return 1;   
        }
    } else 
        printf("introduza comandos: \n");
    yyparse(); 
    return 0;
}

Answer 1

These two rows in your scanner specification both match space:

.          {return yytext[0];}
[ \n\t]    {  }

When you type ESCREVER 1; the space is interpreted by the first rule. Since Flex uses the rules in the order they are written, you can just move the blank-ignoring rule up, so it is checked first.