[Eranga]

Not only that root. If you take that line of code outside of the while loop the correct one should be,

Code:

average = (sum + 1)/(counter - 1) ;

because he update the counter also inside the while loop and for the input -1 also counter updates by one.

Here is much better way, which I really loved to used in my programming.

Code:

import java.util.*;

public class ex {

    public static void main(String[] args) {

        double sum = 0;
        int counter = 0;
        double input = 0;

        do {
            System.out.print("ENTER A GRADE (OR ENTER -1 TO EXIT) ");
            input = new Scanner(System.in).nextDouble();
        
            if(input != -1) {
                sum += input;
                counter++;
            }
            else {
                break;
            }
        }while (true);
        System.out.println("\nThe average is " + (sum/counter) );
    }
}