用Lex(flex)和yacc(bison)写的简单计算器(1)

Lex文件如下：
  %{
#include "cal.tab.h"
%}
%option noyywrap
integer      [0-9]+
dreal        ([0-9]*"."[0-9]+)
ereal        ([0-9]*"."[0-9]+[EedD][+-]?[0-9]+)
real         {dreal}{ereal}
nl           \n
plus         "+"
minus        "-"
times        "*"
divide       "/"
lp           "("
rp           ")"
module       "%"
power        "^"
%%
[ \t]        ;  /*skip any blanks */
{integer}    { sscanf(yytext, "%d", &yylval.integer);
               return INTEGER;
             }
{real}       { sscanf(yytext, "%lf", &yylval.real);/*yylval = atof(yytext);  it doesn't work under MSVSC*/
               return REAL;
              }

{plus}       { return PLUS;}
{minus}      { return MINUS;}
{times}      { return TIMES;}
{divide}     { return DIVIDE;}
{module}     { return MODULE;}
{power}      { return POWER;}
{lp}         { return LP;}