MarksAverager

import java.util.Scanner;
import java.util.ArrayList;

public class MarksAverager3
{

	public static void main(String[] args)
	{

		// Display a title or description
		System.out.println("The Marks Averager (version 3)\n");
		System.out.println("Enter all your marks and then enter a negative mark to finish...\n");

		// Create a Scanner object for obtaining user inputs
		Scanner input = new Scanner(System.in);

		// Create an ArrayList to hold ALL the marks, each mark is type Double
		// Note that 'Double' is like 'double' except it's an object instead of a primitive
		ArrayList<Double> marksArray = new ArrayList<Double>();

		// Loop to enter marks
		double mark;
		do
		{
			System.out.print("Enter another mark: ");
			mark = input.nextDouble();

			if( mark >= 0 )
			{
				// Not the sentinel value, so add this mark to the ArrayList
				marksArray.add( mark );
			}

		} while( mark >= 0 );

		// Report the number of marks
		System.out.println("\nYou've entered " + marksArray.size() + " marks.");

		// Calculate and report the average
		double total = 0;
		for(int i = 0; i < marksArray.size(); i++)
		{
			total += marksArray.get(i);	// Gets the element at index i
		}
		double average = total / marksArray.size();
		System.out.println("The average mark is " + average + ".");

		// Close the Scanner object
		input.close();
	}

}