import java.util.Scanner;

/**
 * Simple calculator that reads infix expressions and evaluates them.
 *   @author Dave Reed
 *   @version 4/13/05
 */
public class Calculator
{
	public static void main(String[] args)
	{
	    Scanner input = new Scanner(System.in);

        System.out.print("Enter an expression (or hit RETURN to stop): ");
	    String line = input.nextLine();
	    
	    while (line.length() > 0) {
	        Expression expr = new InfixExpression(line);
	        
	        if (expr.verify()) {
	            System.out.println(expr.evaluate());
	        }
	        else {
	            System.out.println("INVALID EXPRESSION");
	        }
	        
	        System.out.print("Enter an expression (or hit RETURN to stop): ");
	        line = input.nextLine();
	    }
	    
	    System.out.println("DONE");
	}
}