// Prog: rpn_template.cpp
// Author: ...
// evaluates expressions in reverse polish notation (RPN)

#include<iostream>
#include<sstream>
#include<stack>
#include<cassert>

// POST: leading whitespace characters are extracted
//       from is, and the first non-whitespace character
//       is returned (0 if there is no such character)
char lookahead (std::istream& is)
{
  is >> std::ws;         // skip whitespaces
  if (is.eof())
    return 0;            // end of stream
  else
    return is.peek();    // next character in is
}

// PRE:  in = e, an expression in RPN
// POST: in is empty, and the value of e is returned
double evaluate (std::istream& in)
{
  return 0; // ... to do!
}

int main() 
{
  std::stringstream input1 ("1 2 +");                 // 3
  std::stringstream input2 ("4 2 - 5 4 + *");         // 18
  std::stringstream input3 ("3.0 1.5 * 1.5 3.0 * -"); // 0
  std::cout << evaluate (input1) << "\n";
  std::cout << evaluate (input2) << "\n";
  std::cout << evaluate (input3) << "\n";
  
  return 0;
}