Problem with While Loop.

Question

Hi guys,
i'm doing a pass exam java question, below is the question criteria.
Write a program that allows a user to enter their mark attained in each unit and displays their grade. After all marks are entered the average mark is displayed.
The main method should:
Prompt the user to enter the number of units taken (check for NumberFormatException)
Write a for loop to repeat for each subject, where each iteration
Prompts the user to enter a mark ( a double) for unit 1, unit 2 etc. This should be in a while loop so if mark entered is less than 0 or greater than 100 the prompt will be repeated.
Pass the mark to a method called getGrade.
Display the returned grade
Accumulate each mark
Print the average mark to 2 decimal places
The getGrade method should:
Accept the parameter passed from the main method
Determine the grade according to the following scale
Return the grade
The words that i highlighted in bold is the criteria.
As you can see from the above question, i create an array , even though the question does not prompt me to create as what i know from tackling JavaQuestions "if it does not prompt me to add a criteria, it is ok to add it" :)
below is my program code , in which the result i get is the same as the question result. BUT, from the above question it ask me to add a while loop, so if mark entered is less than 0 or greater than 100 the prompt will be repeated.
But instead i use a do loop. :(
so can anyone help me or show me how to create the while loop for mark entered is less than 0 or greater than 100 the prompt will be repeated, from my program code below. cause i want to know whether it possible to have a while loop instead of do loop for the my program and the while loop can work with an array criteria.
thanks
htw.
import javax.swing.*;
import java.text.DecimalFormat;
public class Mark
    public static void main (String [] args)
        String unitStr;
        String markEnterStr;
        int validUnit;
        double total = 0;
        boolean validInput = true;
        DecimalFormat fmt = new DecimalFormat("#0.00");
        while (validInput)
        unitStr = JOptionPane.showInputDialog(null,"Enter number of units: ");
        try
        validUnit = Integer.parseInt(unitStr);
        double[] markArray = new double[validUnit];
        validInput = false;
        for (int index = 0;index < validUnit; index++)
            do
            markEnterStr = JOptionPane.showInputDialog("Please enter mark " +(index+1) +":");           
            markArray[index] = Double.parseDouble(markEnterStr);
            while(markArray[index] < 0 || markArray[index] >100);
            String correctMark = getGrade(markArray[index]);
            System.out.println(correctMark);
            total = total + markArray[index];       
        double average = (double)total / validUnit;
        System.out.println("Average = " +fmt.format(average));                   
        catch (NumberFormatException e)
        public static String getGrade(double x)
            String grade;
            if (x < 50)
            grade = "Fail";
            else if (x < 60)
            grade = "Pass";
            else if (x < 70)
            grade = "Credit";
            else if (x < 80)
            grade = "Distinction";
            else grade = "High distinction";
            return grade;
}

Answer 1

Hope u got it.
           markArray[index] = -1;
            while(markArray[index] < 0 || markArray[index] >100);
            markEnterStr = JOptionPane.showInputDialog("Please enter mark " +(index+1) +":");           
            markArray[index] = Double.parseDouble(markEnterStr);
            }VJ