/******************************************************
 *PRELIMINARY VERSION without exception handling.
 *Simple line-oriented calculator program. The class
 *can also be used to create other calculator programs.
 *****************************************************/
public class PrelimCalculator
{
    private double result;
    private double precision = 0.0001;
    //Numbers this close to zero are treated as if equal to zero.


    public static void main(String[] args)
                                   throws DivideByZeroException,
                                  UnknownOpException
    {
        PrelimCalculator clerk = new PrelimCalculator();

        System.out.println("Calculator is on.");
        System.out.print("Format of each line: ");
        System.out.println("operator number");
        System.out.println("For example: + 3");
        System.out.println("To end, enter the letter e.");
        clerk.doCalculation();

        System.out.println("The final result is "
                      + clerk.resultValue());
        System.out.println("Calculator program ending.");
    }

    public PrelimCalculator()
    {
        result = 0;
    }

    public void reset()
    {
        result = 0;
    }

    public void setResult(double newResult)
    {
        result = newResult;
    }

    public double resultValue()
    {
        return result;
    }

    public void doCalculation() throws DivideByZeroException,
                                      UnknownOpException
    {
        char nextOp;
        double nextNumber;
        boolean done = false;
        result = 0;
        System.out.println("result = " + result);

        while (! done)
        {
            nextOp = SavitchIn.readNonwhiteChar();
            if ((nextOp == 'e') || (nextOp == 'E'))
                done = true;
            else
            {
                nextNumber = SavitchIn.readLineDouble();
                result = evaluate(nextOp, result, nextNumber);
                System.out.println("result " + nextOp + " "
                                    + nextNumber + " = " + result);
                System.out.println("updated result = " + result);
            }
        }
    }


    /*************************************************************
     *Returns n1 op n2, provided op is one of '+', '–', '*',or '/'.
     *Any other value of op throws UnknownOpException.
     *************************************************************/
    public double evaluate(char op, double n1, double n2)
                                   throws DivideByZeroException,
                                        UnknownOpException
    {
        double answer;
        switch (op)
        {
            case '+':
                answer = n1 + n2;
                break;
            case '-':
                answer = n1 - n2;
                break;
            case '*':
                answer = n1 * n2;
                break;
            case '/':
                if ( (-precision < n2) && (n2 < precision))
                    throw new DivideByZeroException();
                answer = n1/n2;
                break;
            default:
                throw new UnknownOpException(op);
       }

       return answer;
    }
}