Why my calculator always reports "syntax error"?

It's based on this article but uses lex instead of implement it myself.

But I've tried various expressions like 2+3,all failed...

lex:

0   {
        yylval = atoi(yytext);
    }

[1-9][0-9]* {
                yylval = atoi(yytext);
                return NUM;
            }

[-+*/()]    {
                return *yytext;
            }

[ \t\n]+    ;

.           yyerror("Unknown character");

yacc:

%start prob

%token NUM

%%

prob开发者_StackOverflow社区 : expr '\n'
{
    printf("\t=%X\n", $1);
    return 0;
}
;

expr : expr '+' term
{
    $$ = $1 + $3;
}
| expr '-' term
{
    $$ = $1 - $3;
}
| term
{
    $$ = $1;
}
;

term : term '*' NUM
{
    $$ = $1 * $3;
}
| term '/' NUM
{
    $$ = $1/$3;
}
| '(' expr ')'
{
    $$ = $2;
}
| NUM
{
    $$ = $1;
}
;

%%

It's because of :

[ \t\n]+    ; 

Move \n to [-+*/()].

first upon remove test for 0 i.e.

0   {
    yylval = atoi(yytext);
}

this wont help you.this should work now.