import javax.swing.JOptionPane;

import javax.swing.JOptionPane;

public class LetterConversion
{
    public static void main(String [ ] args)
    {
        //You must first declare the necessary constants needed
        //to run the program.
        
        //MAX_GRADE is important to declare because you need to ensure invalid
        //input will not receive a letter grade.
        final int MAX_GRADE = 100;
        
        //Minimum letter grades must be declared to ensure the complete 
        //range of grades are accounted for.
        final int MIN_A = 80;
        final int MIN_B = 70;
        final int MIN_C = 60;
        final int MIN_D = 50;
        final int MIN_F = 0;
        
        //The actual char of each letter grade.  This must be declared 
        //to prevent from bad programming practice.
        final char LET_A = 'A';
        final char LET_B = 'B';
        final char LET_C = 'C';
        final char LET_D = 'D';
        final char LET_F = 'F';
        
        //String constants are also declared for efficiency.
        final String COLON = ": ";
        final String ABOVE_AVG = "The grade is above average.";
        final String AVG = "The grade is average.";
        final String BELOW_AVG = "The grade is below average.";
        
        String input;             //The string that the user inputs will be stored here.
        int grade=0;              //An int is needed to convert the String input for integer comparison.
        String result="";         //The String of items needed for output.
        
        //The program asks the user for a numerical grade.
        input = JOptionPane.showInputDialog("Please enter the numerical grade to be converted: ");
        
        //Integer.parseInt converts a String to an int.
        grade = Integer.parseInt(input);
        
        //This first if statement ensures that the grade provided by the 
        //user is valid.  Note the use of constants here.
        if(MAX_GRADE >= grade && grade >= MIN_F) 
        {
            //The second layer of nested if statements determine
            //what category the numerical grade is in.  This layer
            //is nested inside a validity check to ensure that any
            //invalid input will not generate a valid output.
            if(grade >= MIN_A)
            {
                System.out.print(LET_A);
                result= ABOVE_AVG;
            }
            else if(grade >= MIN_C)
            {
                //The third layer of nested if statements determine
                //the letter grade value of the numerical grade.  The
                //letter is printed out without the next line so the
                //output looks continuous.
                if(grade >= MIN_B)
                {
                    System.out.print(LET_B);
                }
                else
                {
                    System.out.print(LET_C);
                }
                result = AVG;
            }
            else if(grade >= MIN_F)
            {
                if(grade >= MIN_D)
                {
                    System.out.print(LET_D);
                }
                else
                {
                    System.out.print(LET_F);
                }
                result = BELOW_AVG;
            }
            System.out.print(COLON);
        }
        else
        {
            result += "Error: not a valid numerical grade.";
        }
        
            
        System.out.println(result);
        
    }
}