Assignment3.java

import java.util.InputMismatchException;
import java.util.Scanner;

class InvalidMarksException extends Exception {
    public InvalidMarksException(String message) {
        super(message);
    }
}

class Student {
    private int rollNumber;
    private String studentName;
    private int[] marks;

    public Student(int rollNumber, String studentName, int[] marks) throws InvalidMarksException {
        this.rollNumber = rollNumber;
        this.studentName = studentName;
        this.marks = marks;
        validateMarks();
    }

    private void validateMarks() throws InvalidMarksException {
        for (int i = 0; i < marks.length; i++) {
            if (marks[i] < 0 || marks[i] > 100) {
                throw new InvalidMarksException("Invalid marks for subject " + (i + 1) + ": " + marks[i]);
            }
        }
    }

    public double calculateAverage() {
        if (marks == null || marks.length == 0) {
            return 0.0;
        }
        int sum = 0;
        for (int mark : marks) {
            sum += mark;
        }
        return (double) sum / marks.length;
    }

    public void displayResult() {
        System.out.println("Roll Number: " + rollNumber);
        System.out.println("Student Name: " + studentName);
        
        System.out.print("Marks: ");
        for (int mark : marks) {
            System.out.print(mark + " ");
        }
        System.out.println();
        
        double avg = calculateAverage();
        System.out.println("Average: " + avg);

        String resultStatus = avg >= 40.0 ? "Pass" : "Fail";
        System.out.println("Result: " + resultStatus);
    }

    public int getRollNumber() {
        return rollNumber;
    }
}

public class Main {
    private Student[] students;
    private int studentCount;
    private Scanner scanner;
    private static final int MAX_STUDENTS = 10; 

    public Main() {
        students = new Student[MAX_STUDENTS];
        studentCount = 0;
        scanner = new Scanner(System.in);
    }

    public void addStudent() {
        int rollNumber = 0;
        String studentName = "";
        int[] marks = new int[3]; 

        System.out.print("Enter Roll Number: ");
        try {
            rollNumber = scanner.nextInt();
            scanner.nextLine(); 
        } catch (InputMismatchException e) {
            System.out.println("Error: Invalid input for Roll Number. Must be an integer.");
            scanner.nextLine(); 
            return; 
        }

        System.out.print("Enter Student Name: ");
        try {
             studentName = scanner.nextLine();
        } catch (Exception e) {
            System.out.println("Error: Could not read student name.");
            return;
        }
       

        for (int i = 0; i < marks.length; i++) {
            System.out.print("Enter marks for subject " + (i + 1) + ": ");
            try {
                marks[i] = scanner.nextInt();
            } catch (InputMismatchException e) {
                System.out.println("Error: Invalid input for marks. Must be an integer.");
                scanner.nextLine(); 
                return; 
            }
        }
        scanner.nextLine(); 

        try {
            Student newStudent = new Student(rollNumber, studentName, marks);
            students[studentCount++] = newStudent;
            System.out.println("Student added successfully. Returning to main menu...");
        } catch (InvalidMarksException e) {
            System.out.println("Error: " + e.getMessage() + " Returning to main menu...");
        } catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("Error: Maximum student limit reached (" + MAX_STUDENTS + ").");
        }
    }

    public void showStudentDetails() {
        System.out.print("Enter Roll Number to search: ");
        try {
            int searchRoll = scanner.nextInt();
            scanner.nextLine(); 

            Student foundStudent = null;
            for (int i = 0; i < studentCount; i++) {
                if (students[i].getRollNumber() == searchRoll) {
                    foundStudent = students[i];
                    break;
                }
            }

            if (foundStudent != null) {
                foundStudent.displayResult();
            } else {
                System.out.println("Error: Student with Roll Number " + searchRoll + " not found.");
            }
            System.out.println("Search completed.");
        } catch (InputMismatchException e) {
            System.out.println("Error: Invalid input for Roll Number. Must be an integer.");
            scanner.nextLine(); 
        }
    }

    public void mainMenu() {
        int choice = 0;
        do {
            System.out.println("\n===== Student Result Management System =====");
            System.out.println("1. Add Student");
            System.out.println("2. Show Student Details");
            System.out.println("3. Exit");
            System.out.print("Enter your choice: ");

            try {
                choice = scanner.nextInt();
                scanner.nextLine(); 

                switch (choice) {
                    case 1:
                        addStudent();
                        break;
                    case 2:
                        showStudentDetails();
                        break;
                    case 3:
                        System.out.println("Exiting program. Thank you!");
                        break;
                    default:
                        System.out.println("Invalid choice. Please enter 1, 2, or 3.");
                }
            } catch (InputMismatchException e) {
                System.out.println("Error: Invalid input. Please enter a number (1, 2, or 3).");
                choice = 0; 
                scanner.nextLine(); 
            }
        } while (choice != 3);
    }

    public static void main(String[] args) {
        Main manager = new Main();
        try {
            manager.mainMenu();
        } finally {
            if (manager.scanner != null) {
                manager.scanner.close(); 
                System.out.println("Scanner resource released."); 
            }
        }
    }
}