import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;

public class GolfScores
{
    public static final int MAX_NUMBER_SCORES = 10;

    /**
     Shows differences between each of a list of golf scores and their average.
    */
    public static void main(String[] args) throws IOException
    {
        double[] score = new double[MAX_NUMBER_SCORES];
        int numberUsed = 0;

        System.out.println("This program reads golf scores and shows");
        System.out.println("how much each differs from the average.");

        System.out.println("Enter golf scores:");
        numberUsed = fillArray(score);
        showDifference(score, numberUsed);
    }

    /**
     Reads values into the array a. Returns the number of values placed in the array a.
    */
    public static int fillArray(double[] a) throws IOException
    {
        System.out.println("Enter up to " + a.length
                               + " nonnegative numbers, one per line.");
        System.out.println("Mark the end of the list with a negative number.");
        BufferedReader keyboard = new BufferedReader(
                                       new InputStreamReader(System.in));

        double next;
        int index = 0;
        next = stringToDouble(keyboard.readLine( ));
        while ((next >= 0) && (index < a.length))
        {
            a[index] = next;
            index++;
            next = stringToDouble(keyboard.readLine( ));
           //index is the number of array indexed variables used so far.
        }
       //index is the total number of array indexed variables used.

        if (next >= 0)
             System.out.println("Could only read in "
                                + a.length + " input values.");

        return index;
    } 

    /**
     Precondition: numberUsed <= a.length.
                   a[0] through a[numberUsed-1] have values.
     Returns the average of numbers a[0] through a[numberUsed-1].
    */
    public static double computeAverage(double[] a, int numberUsed)
    {
        double total = 0;
        for (int index = 0; index < numberUsed; index++)
            total = total + a[index];
        if (numberUsed > 0)
        {
            return (total/numberUsed);
        }
        else
        {
            System.out.println("ERROR: Trying to average 0 numbers.");
            System.out.println("computeAverage returns 0.");
            return 0;
        }
     }
 
     private static double stringToDouble(String stringObject)
     {
         return Double.parseDouble(stringObject.trim( ));
     }
 
     /**
      Precondition: numberUsed <= a.length.
                    The first numberUsed indexed variables of a have values.
       Postcondition: Gives screen output showing how much each of the first
       numberUsed elements of the array a differ from their average.
     */
     public static void showDifference(double[] a, int numberUsed)
     {
         double average = computeAverage(a, numberUsed);
         System.out.println("Average of the " + numberUsed
                                              + " scores = " + average);
         System.out.println("The scores are:");
         for (int index = 0; index < numberUsed; index++)
         System.out.println(a[index] + " differs from average by "
                                     + (a[index] - average));
     }
 }