u013052928 于 2016.02.28 23:11 提问

bison简易计算器 新手问题

``````这是1.l:
%{
# include "2.tab.h"
%}
%%
"-"         { return SUB; }
"*"         { return MUL; }
"/"         { return DIV; }
"|"         { return ABS; }
[0-9]+  {yylval=atoi(yytext); return NUMBER;}
\t     {/* ignore whitespace */}
.       {printf("character %c\n",*yytext);}
\n      {return EOL;}

%%
int yywrap(void){
return 0;
}

``````
``````%{
#include <stdio.h>
int yylex (void);
void yyerror (char const *);
%}
/* declare tokens */
%token NUMBER
%token ADD SUB MUL DIV ABS
%token EOL
%%
calclist: /* nothing */
| calclist exp EOL { printf("= %d\n", \$1); }
;
exp: factor
| exp ADD factor { \$\$ = \$1 + \$3; }
| exp SUB factor { \$\$ = \$1 - \$3; }
;
factor: term
| factor MUL term { \$\$ = \$1 * \$3; }
| factor DIV term { \$\$ = \$1 / \$3; }
;
term: NUMBER
| ABS term { \$\$ = \$2 >= 0? \$2 : - \$2; }
;
%%
main(int argc, char **argv)
{
yyparse();
}
void yyerror(char const *s)
{
fprintf(stderr, "error: %s\n", s);
}

``````

1个回答

devmiao      2016.02.28 23:23