[請益] yacc與lex 四則運算

[aa1727 (Sean)]

先附上程式碼：
Lex:
%{
#include <stdio.h>
#include "y.tab.h"

%}

%option noyywrap

%%

[0-9]+ { yylval = atoi(yytext); return INTEGER; }
[\+\-\*\/\(\)\n] { return *yytext; }
[\t] {}
. { yyerror("invalid char."); }
%%

Yacc:
%{
#include <stdio.h>
#include <stdlib.h>
#include "y.tab.h"
int yylex();

%}

%token INTEGER
%left '+' '-'
%left '*' '/'
%nonassoc UMINUS
%%

program:
    |program expression '\n' { printf("Ans : %d\n\n", $2); }
    ;

expression :
    INTEGER { $$ = $1; }
    | expression  '+' expression  { $$ = $1 + $3;
                printf("%d + %d = %d \n",$1,$3,$$);}
    | expression  '-' expression  { $$ = $1 - $3;
                printf("%d - %d = %d \n",$1,$3,$$);}
    | expression  '*' expression  { $$ = $1 * $3;
                printf("%d * %d = %d \n",$1,$3,$$);}
    | expression  '/' expression  { $$ = $1 / $3;
                printf("%d / %d = %d \n",$1,$3,$$);}
    | '-' expression  %prec UMINUS { $$ = -$2; }
    | '(' expression  ')' { $$ = $2; }
    | { yyerror("invalid input.\n"); }
    ;

%%
int main()
{
    yyparse();
    return 0;
}
void yyerror(char *msg)
{
   printf("Error: %s \n",msg);
}


要實現 +-*/()和負數四則運算

不知道為什麼最後會出現
syntax error

https://i.imgur.com/PkahB5J.jpg

搞整個週末了實在沒辦法只能求大神了



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※ 編輯: aa1727 (39.10.237.189), 12/17/2018 02:59:02
推 CindyLinz: 你 program 沒有可以結束的 rule 啊