GradeCalculatorSystem.java

import java.util.Scanner;

// The Grader Class
class Grader {
    // Instance variable
    private double score;

    // Suitable constructor
    public Grader(double score) {
        this.score = score;
    }

    // Method to calculate and return the letter grade
    public char letterGrade() {
        if (score >= 90 && score <= 100) {
            return 'O'; // Outstanding
        } else if (score >= 80 && score < 90) {
            return 'E'; // Excellent
        } else if (score >= 70 && score < 80) {
            return 'A'; // Very Good
        } else if (score >= 60 && score < 70) {
            return 'B'; // Good
        } else if (score >= 50 && score < 60) {
            return 'C'; // Fair
        } else {
            return 'F'; // Fail (0 to 49)
        }
    }
}

// Sample Testing Class (PascalCase)
public class GradeCalculatorSystem {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("--- Student Grading System ---");

        double validScore = -1;
        boolean isValid = false;

        // Loop until a valid score between 0 and 100 is provided
        while (!isValid) {
            System.out.print("Please enter a score (0 - 100): ");
            validScore = getValidDouble(scanner);

            // Confirming the value is between 0 and 100
            if (validScore >= 0 && validScore <= 100) {
                isValid = true;
            } else {
                System.out.println("Error: Score must be between 0 and 100. Please try again.");
            }
        }

        // Generate the Grader object once confirmed
        Grader studentGrader = new Grader(validScore);

        // Obtain and print the Grade
        char finalGrade = studentGrader.letterGrade();
        System.out.println("\n==================================");
        System.out.println("Score Entered: " + validScore);
        System.out.println("Final Letter Grade: " + finalGrade);
        System.out.println("==================================");

        scanner.close();
    }

    // Helper method to ensure program doesn't crash on invalid (non-numeric) input
    private static double getValidDouble(Scanner scanner) {
        while (!scanner.hasNextDouble()) {
            System.out.print("Invalid input. Please enter a valid number: ");
            scanner.next(); // Consume invalid input
        }
        return scanner.nextDouble();
    }
}