//BooleanTest.java
/*
boolean data type.
only 2 values: true false (reserved words).

Useful for true/false kind of data: checked/unchecked
*/

import java.awt.*;
import javax.swing.*;

public class BooleanTest extends JApplet {    

    public static void main(String[] argv) {
    //public void init() {

	String input;
	char grade;
	boolean badGrade;   //can be true or can be false, no other values.
	
	do {
	    input = JOptionPane.showInputDialog("Enter a grade");
	    grade = input.charAt(0);
	    grade = Character.toUpperCase(grade);
	    badGrade = false;    //assume is valid grade
	    if (grade!='A' && grade!='B' && grade!='C' && 
		grade!='D' && grade!='F' && grade!='S' && 
		grade!='N') {
		
		JOptionPane.showMessageDialog(null,
				 "ERROR invalid grade.  "+
				    "Must be A, B, C, D, F, S, or N\n"+
				    "Reenter this classes' grade.",
				  "Bad input",
				  JOptionPane.ERROR_MESSAGE);
		badGrade = true;   //no, it's bad
	    }
	} while (badGrade);   //loop if true

	JOptionPane.showMessageDialog(null, "Valid grade: " + grade); 

	//*****************************************************
	int year;
	boolean isLeap;

	do {
	    input = JOptionPane.showInputDialog("Enter a year (0 to quit)" );
	    year = Integer.parseInt(input);

	    if (year%4==0 && year%100!=0 || year%400==0)
		isLeap = true;     //remember for later if leap year or not 
	    else
		isLeap = false;
	    
	    if (isLeap)    //if is true
		JOptionPane.showMessageDialog(null, "Is a leap year"); 
	    else           //else is false
		JOptionPane.showMessageDialog(null, "Is not a leap year"); 
	} while (year != 0);
    }
}