import java.util.Arrays;

    // A Student with a grades array
    public class StudentGr {   
	private String name;
	private String id;
	private int[] grades;
	
	public StudentGr (String name, String id)
	{
		this.name = name;
		this.id = id;
		grades = new int[0];
	}

	public String getName() {
		return name;
	}
	
	public String getID(){
		return id;
	}
	
	public int numGrades() {
		return grades.length;
	}
	
	public int getGrade(int i){
		if (i < 0 || i >= numGrades()){
			return -1;
		}
		return grades[i];
	}
	
	private double getAverage(){
		double total = 0.0;
		for (int i=0; i<grades.length; i++) {
			total += grades[i];
		}
		return total / grades.length;
	}
	
	public void addGrade (int newGrade)
	{
		int [] newGrades = new int[numGrades() + 1];
		for (int i = 0; i < numGrades(); i++){
			newGrades[i] = grades[i];
		}
		newGrades[numGrades()] = newGrade;
		grades = newGrades;
	}
	
	public void changeGrade(int newGrade, int whichGrade) {
		if ((whichGrade < grades.length) && (whichGrade >= 0)) {
			grades[whichGrade] = newGrade;
		}
	}
	
	public String toString()
	{
		String outputString = "name: " + name + "\t" + "id: " + id + "\t" + 
	                          "average grade: " + getAverage() + "\t" + "grades: " +
				               Arrays.toString(grades);

		return(outputString);
	}
	
	public static void main(String[] args){
		StudentGr jack = new StudentGr("Jack","1234");
		jack.addGrade(85);
		jack.addGrade(90);
		System.out.println("Jack's grade number 0: " + jack.getGrade(0));
		System.out.println(jack);
		
		StudentGr mary = new StudentGr("Mary", "2345");
		mary.addGrade(93);
		mary.addGrade(90);
		mary.addGrade(96);
		System.out.println(mary);
		mary.changeGrade(99,1);
		System.out.println(mary);		
	}
}