Notes

import javax.swing.*;

public class GradeCalculator {
private JFrame frame;
private int totalGrades;
private int sumGrades;

public static void main(String[] args) {
GradeCalculator calculator = new GradeCalculator();
calculator.createGUI();
}

public void createGUI() {
frame = new JFrame("Grade Calculator");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

while (true) {
String input = JOptionPane.showInputDialog(frame, "Enter 1, 2, or 3:n1 - Enter student gradesn2 - Calculate averagen3 - Exit");

if (input == null || input.equals("3")) {
// Exit the program
System.exit(0);
} else if (input.equals("1")) {
enterGrades();
} else if (input.equals("2")) {
calculateAverage();
}
}
}

private void enterGrades() {
int numStudents = Integer.parseInt(JOptionPane.showInputDialog(frame, "Enter the number of students:"));
for (int i = 1; i <= numStudents; i++) {
String studentName = JOptionPane.showInputDialog(frame, "Enter student " + i + "'s name:");
int grade = -1;
while (grade < 0 || grade > 100) {
try {
grade = Integer.parseInt(JOptionPane.showInputDialog(frame, "Enter " + studentName + "'s grade (0-100):"));
if (grade < 0 || grade > 100) {
JOptionPane.showMessageDialog(frame, "Grade must be between 0 and 100.");
}
} catch (NumberFormatException e) {
JOptionPane.showMessageDialog(frame, "Invalid input. Please enter a number.");
}
}
totalGrades++;
sumGrades += grade;
}
}

private void calculateAverage() {
if (totalGrades == 0) {
JOptionPane.showMessageDialog(frame, "No grades submitted yet.");
} else {
double average = (double) sumGrades / totalGrades;
JOptionPane.showMessageDialog(frame, "Average grade: " + average);
}
}
}