/* Copyright (C) 2014 by Alexandru Cojocaru */

/* This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>. */


#include <stdio.h>
#include <stdlib.h>
#include <error.h>
#include <errno.h>

#define STRINGIZE(m) #m
#define STRINGIZE2(m) STRINGIZE(m)

#define N_MAXDIGS 10
enum {
  STMAXDEPTH = 100,
};

static double stack[STMAXDEPTH];
static int stackind = 0;

static int
checkargs (int needed)
{
  if (stackind < needed)
    error (1, 0, "stack underflow: args present %d, args needed %d\n",
	   stackind, needed);
}
	     
static int
skipws (FILE *in)
{
  int c;
  do
    c = getc (in);
  while (isspace (c));
  ungetc (c, in);
}

static int
getnum (FILE *in)
{
  double v;
  char buf[N_MAXDIGS + 1];
  char *tailp = NULL;
  char *p = buf;
  int c;
  
  fscanf (in, "%" STRINGIZE2 (N_MAXDIGS) "s", buf);

  errno = 0;
  v = strtod (buf, &tailp);

  if (errno != 0 || (tailp != NULL && *tailp != '\0'))
    error (1, errno, "can't decode number: `%s'\n", buf, tailp);

  printf ("v: %f\n", v);

  stack[stackind] = v;

  return 1;
}
   
/* return: EOF on EOF, 0 on failure, 1 on success */

static int
next (FILE *in)
{
  int c;
  int r = 1;

  if (stackind == STMAXDEPTH)
    error (1, 0, "exceded stack limit of %u\n", STMAXDEPTH);
 
  skipws (in);

  c = getc (in);

  switch (c) {
  case '0' ... '9':
    ungetc (c, in);
    r = getnum (in);
    break;
  case '+':; case '-':;
    int nextc = getc (in);
    ungetc (nextc, in);
    if (isdigit (nextc)) {
      r = getnum (in);
      break;
    }
  case '*': case '/':  /* fail trough */
    checkargs (2);
    double res;
    switch (c) {
    case '+': res = stack[stackind - 2] + stack[stackind - 1]; break;
    case '-': res = stack[stackind - 2] - stack[stackind - 1]; break;
    case '*': res = stack[stackind - 2] * stack[stackind - 1]; break;
    case '/': res = stack[stackind - 2] / stack[stackind - 1]; break;
    }
    stackind -= 2;
    stack[stackind] = res;
    break;
  case EOF:
    return EOF;
  default:
    printf ("unknown character: %c\n", c);
    break;
  }

  ++stackind;
  return r;
}

int
main (void)
{
  int r;
  while ((r = next (stdin)) == 1)
    ;

  if (r == EOF)
    puts ("EOF");

  if (stackind == 0)
    error (1, 0, "the stack must contain at least one element\n");
  printf ("%f\n", stack[stackind-1]);
}