// This simple example shows how to use stack to evaluate
// a postfix expression. This implementation is limited
// to single digit values, both for operands and for results.
// It is easy to expand it to include any integer values, though.
// dec-03-1998
import java.io.*;

class Expression
{
    static public void main(String[] argv) throws IOException
    {
	LStack S = new LStack();
	String x, op1, op2, result;
	BufferedReader br = new BufferedReader(new InputStreamReader
                                              (System.in));
	String expression;
	
	System.out.println(" type a postfix-expression, ending with # ");
	expression = br.readLine();
	int i = 0;
	x = expression.substring(i,i+1);
	while (!x.equals("#"))  // first read the expression into stack
	{
	    if (isOperand(x) == true)
		S.push(x);
	    else
	    {
		op2 = (String)S.pop();
		op1 = (String)S.pop();
		result = doOperation(x,op1,op2);
		S.push(result);
	    }
	    i ++;
	    x = expression.substring(i,i+1);
	}
	System.out.println(" result is : " + (String)S.topValue());
    } // main

    static boolean isOperand(String x)
    {
	if (x.equals("+") || x.equals("-")
            || x.equals("*") || x.equals("/"))
	    return false;
	else
	    return true;
    } // isOperand

    static String doOperation(String x, String op1, String op2)
    {
	int i, j, r;
	i = Integer.parseInt(op1);
	j = Integer.parseInt(op2);
	if (x.equals("+"))
	    return String.valueOf(i+j);
	else if (x.equals("-"))
	    return String.valueOf(i-j);
	else if (x.equals("*"))
	    return String.valueOf(i*j);
	else if (x.equals("/"))
	    return String.valueOf(i/j);
	return null;
    } // doOperation
}