// minimal comments, postfix.cc, Owen Astrachan, 9/3/93
// modified 9/16/94, modified 1/27/96 for stack/class changes

#include <iostream.h>
#include <ctype.h>                    // for isspace
#include <stdlib.h>                   // for exit
#include "apstack.h"                  

int Operate(char op,const int & left, const int & right);

int main()
{
    apstack<int> s;
    int left,right;
    char c;
    
    while (cin.get(c))              // one char at a time
    {
	if (isdigit(c))
	{
	    cin.putback(c);         // back onto stream for reading
	    cin >> left;            // read number, push it
	    s.push(left);
	}
	else if (isspace(c))        // skip
	{
	    continue;
	}
	else                        // operate char: '*', etc., push
	{
	    s.pop(right);
	    s.pop(left);
	    s.push(Operate(c,left,right));
	}
    }
    // get result (on top of stack)
    if (s.isEmpty())
    {
	cerr << "malformed postfix, stack empty" << endl;
	exit(1);
    }
    s.pop(left);                  // final answer
    if (!s.isEmpty())
    {
	cerr << "malformed postfix, stack not empty" << endl;
    }
    else
    {
	cout << "result = " << left << endl;
    }
}

int Operate(char c,const int & left, const int & right)
// precondition: c in ['+','*','-','/'], represents corresponding op
// postcondition: returns left op right
{
    int result;
    switch(c)
    {
      case '+':
	result = left+right;
	break;
      case '*':
	result =  left*right;
	break;
      case '-':
	result =  left-right;
	break;
      case '/':
	result = left/right;
	break;
      default:
	result = 0;
	break;
    }
    return result;
}