import java.util.*;

public class PostfixExpressionEvaluater {
	//Data for all objects
	private static final String operators = "+-*/";

	//Private method
	private static boolean isOperator(char arg) {
		return operators.indexOf(arg) != -1;
	}

	//Public method
	public int evaluate(String str) throws ArithmeticException {
		StackOfIntegers stack = new StackOfIntegers(str.length());
		
		for(int i = 0; i < str.length(); i++) {
			try {
				char c = str.charAt(i);
				int number = -1;
				if(c >= '0' && c <= '9') {
					number = 0;
					while(c != ' ') {
						number = number * 10 + (c - '0');
						i++;
						c = str.charAt(i);
					}
					stack.push(number);
					System.out.println("Pushed constant " + number);
				}
				else if (isOperator(c)) {
					int x,y,answer=0;
                	y = stack.pop();
                	System.out.println("Popped the right operand " + y + " of the " + c);
                	x = stack.pop();
               		System.out.println("Popped the left operand " + x + " of the " + c);
                	switch (c) {
                		case '+':	answer = x + y;
                					break;
                		case '-':	answer = x - y;
                					break;
                		case '*':	answer = x * y;
                					break;
                		case '/':	answer = x / y;
                					break;
                	}
                	stack.push(answer);
                	System.out.println("Evaluated " + c +" and pushed "+ answer);	
				}
				else
					throw new ArithmeticException("Invalid operator found: " + c);
			}catch(EmptyStackException e) {
				throw new ArithmeticException("Not enough numbers in expression!");}
		}//for
		
		if(stack.isEmpty())
			throw new ArithmeticException("No expression provided!");
		int value = stack.pop();
		System.out.println("Popped " + value + " at end of expression.");		
		if (!stack.isEmpty()) 
			throw new ArithmeticException("Not enough operators for all the numbers!");
		return value; 
	}//method
}//class

class TestPostfixExpressionEvaluater {
	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		System.out.println("To stop testing enter: No more");
		System.out.println("Starting...");
		while(true) {
			System.out.print("     Expression: ");
			String expression = s.nextLine();
			if(expression.equals("No more")) {
				System.out.println("End of test!");
				break;
			}
			else {
				try {
					PostfixExpressionEvaluater w = new PostfixExpressionEvaluater();
					System.out.println("Value = "+w.evaluate(expression));
				}catch(ArithmeticException e) {
					System.out.println(e.getMessage()); }
			}
		}
	}	
}
/*

1 2 +7 +
10 5 2 3 +/
1 2 +++
1 2 &
10 2 15 3 12 +/*-
2 15 12 -17 *-
1 2 3 4 5 6 7 ++++++
12 0 /
*/