cal.y
%{
#include <stdio.h>
#include "lex.yy.c"
#define YYSTYPE int
int yyparse(void);
%}
%token INTEGER PLUS MINUS TIMES DIVIDE LP RP
%%
command : exp {printf("%d/n",$1);}
exp: exp PLUS term {$$ = $1 + $3;}
|exp MINUS term {$$ = $1 - $3;}
|term {$$ = $1;}
;
term : term TIMES factor {$$ = $1 * $3;}
|term DIVIDE factor {$$ = $1/$3;}
|factor {$$ = $1;}
;
factor : INTEGER {$$ = $1;}
| LP exp RP {$$ = $2;}
;
%%
int main()
{
return yyparse();
}
void yyerror(char* s)
{
fprintf(stderr,"%s",s);
}
int yywrap()
{
return 1;
}
cal.l
%{
#include<string.h>
#include "y.tab.h"
extern int yylval;
%}
numbers ([0-9])+
plus "+"
minus "-"
times "*"
divide "/"
lp "("
rp ")"
delim [ /n/t]
ws {delim}*
%%
{numbers} {sscanf(yytext, "%d", &yylval); return INTEGER;}
{plus} {return PLUS;}
{minus} {return MINUS;}
{times} {return TIMES;}
{divide} {return DIVIDE;}
{lp} {return LP;}
{rp} {return RP;}
{ws} ;
. {printf("Error");exit(1);}
%%
使用方式:
yacc -d cal.y
lex cal.l
g++ -o cal y.tab.c
運行./cal 然後輸入3+4 ctrl+D就可以看到結果了