import java.util.NoSuchElementException;
   import java.util.StringTokenizer;

/**
 * A 5-function calculator that can evaluate expressions
 * consisting of an integer operand followed by an operator 
 * followed by an integer operand (e.g.,5+3)
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
    public class IntegerCalculator implements ExpressionObserver
   {
      private String         operators;
   
    /**
     * Default Constructor
     */
       public IntegerCalculator()
      {
         operators = new String("%/x-+");
      }
   
   
    /**
     * Evaluate an expression
     *
     * @param  expression   The String containing the expression
     * @return              The result of evaluating the expression
     * @throws ArithmeticException     If an arithmetic problem arises
     * @throws NoSuchElementException  If an operand or operator is missing
     * @throws NumberFormatException   If an operand is not an int
     */
       public int calculate(String expression) throws ArithmeticException, 
       				   NoSuchElementException, 
       				   NumberFormatException
      {
         int                    left, result, right;
         String                 leftS, operator, rightS;
         StringTokenizer        st;
      
      
      // Construct a StringTokenizer that uses the operators
      // as delimiters and returns the delimiters as
      // tokens
         st = new StringTokenizer(expression, operators, true);
      
      
      // Parse the expression
         leftS    = st.nextToken();
         operator = st.nextToken();
         rightS   = st.nextToken();
      
        // Create the left side operand
         left = 0;
      
        // Initialize the left side operand
         left  = Integer.parseInt(leftS);
      
        // Create the right side operand
         right = 0;
      
        // Initialize the right side operand
         right = Integer.parseInt(rightS);
      
      
      // Perform the operation
         if      (operator.equals("%")) result = left % right;
         else if (operator.equals("/")) result = left / right;
         else if (operator.equals("x")) result = left * right;
         else if (operator.equals("-")) result = left - right;
         else                           result = left + right; // "+" 
      
        // Return the result
         return result;
      }
     /**
     * Evaluate an expression and return a String representation of
     * the result (required by ExpressionObserver)
     *
     * @param expression   The expression to evaluate
     * @return             The result (or "Error")
     */
    public String evaluate(String expression)
    {
       String    result;
       

       try
       {
          result = "" + calculate(expression);          
       }
       catch (Exception e)
       {
          result = "Error";          
       }

       return result;       
    }

   }