%{
#include <math.h>
#include <stdio.h>
double akku = 0, eingabe = 0;
char op = '+';
void operiere();
%}
%option main
DIGIT  [0-9]
%%
-?{DIGIT}+(\.)?{DIGIT}*   { eingabe = atof(yytext);
                          operiere();
                        }
-?{DIGIT}*\.{DIGIT}+      { eingabe = atof(yytext);
                          operiere();
                        }
"+"                     |
"-"                     |
"*"                     |
"/"                     op = *yytext;
c                       { akku = 0;
                          op = '+';
                        }
.|\n                    /* nixx */
%%
void operiere() {
  double result = akku;
  switch(op){
    case '+': result = akku+eingabe;
              printf(" => %g", result);              
              break;
    case '-': result = akku-eingabe;
              printf(" => %g", result);
              break;
    case '*': result = akku*eingabe;
              printf(" => %g", result);
              break;
    case '/': result = akku/eingabe;
              printf(" => %g", result);
              break;
  }
  op = ' ';
  akku = result;
}