%{
 /* C declarations */
#define YYSTYPE double
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
void yyerror(char* s) {
   printf("%s\n", s);
}

int yylex(void);
%}
 /* Bison declarations */
%token NUMBER
%left '+' '-'
%left '*' '/'

%%
 /* grammar rules */
input   :               {}
    	| input line    {}
    	;
line    : '\n'          { exit(0); }
        | expr '\n'     { printf("\t%g\n", $1); }
        ;
expr    : NUMBER        { $$ = $1; }
    	| expr '+' expr { $$ = $1 + $3; }
    	| expr '-' expr { $$ = $1 - $3; }
    	| expr '*' expr { $$ = $1 * $3; }
    	| expr '/' expr { $$ = $1 / $3; }
    	| '(' expr ')'  { $$ = $2; }
    	;
%%
 /* additional C code */
int yylex(void) {
  int c;

  do {
    c = getchar();
  } while (c == ' ' || c == '\t');

  if (isdigit(c) || c == '.') {
    ungetc(c, stdin);
    scanf("%lf", &yylval);
    return NUMBER;
  } else if (c == EOF) {
    return 0;
  }
  return c;
}

int main(void) {
  printf("Exit with Ctrl-c\n");
  yyparse();
  return 0;
}