using System;

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using System.Collections.Generic;

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public struct Student

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{

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    public int StudentID;

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    public string FirstName;

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    public string LastName;

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    public Student(int id, string firstName, string lastName)

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    {

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        StudentID = id;

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        FirstName = firstName;

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        LastName = lastName;

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    }

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    public string GetName()

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    {

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        return FirstName + " " + LastName;

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    }

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}

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public class StudentManager

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{

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    private List<Student> students;

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    public StudentManager()

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    {

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        students = new List<Student>();

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    }

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    public void AddStudent(int id, string name)

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    {

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        string[] nameParts = name.Split(',');

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        if (nameParts.Length != 2)

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        {

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            Console.WriteLine("Invalid name format. Name must have a single comma.");

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            return;

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        }

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        students.Add(new Student(id, nameParts[1].Trim(), nameParts[0].Trim()));

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    }

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    public void DisplayEncodedStudentIDs()

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    {

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        students.Sort((x, y) => y.StudentID.CompareTo(x.StudentID));

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        foreach (var student in students)

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        {

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            Console.WriteLine(student.StudentID);

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        }

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    }

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    public void DisplayNamesAlphabetically()

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    {

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        students.Sort((x, y) => (x.FirstName + x.LastName).CompareTo(y.FirstName + y.LastName));

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        foreach (var student in students)

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        {

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            Console.WriteLine(student.FirstName + " " + student.LastName);

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        }

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    }

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    public void DisplayStudentIDAndName()

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    {

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        for (int i = 0; i < students.Count; i++)

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        {

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            Console.WriteLine("{i + 1}: {students[i].StudentID} {students[i].GetName()}");

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        }

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    }

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}

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public class Program

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{

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    public static void Main()

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    {

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        StudentManager manager = new StudentManager();

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        int action = -1;

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        while (action != 0)

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        {

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            Console.WriteLine("1. New Student\n2. Student ID\n3. First Name and Last Name\n4. Student ID and Name\nAction:>");

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            action = Convert.ToInt32(Console.ReadLine());

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            switch (action)

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            {

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                case 1:

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                    Console.WriteLine("Enter Student ID:");

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                    int id = Convert.ToInt32(Console.ReadLine());

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                    Console.WriteLine("Enter Name:");

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                    string name = Console.ReadLine();

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                    manager.AddStudent(id, name);

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                    break;

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                case 2:

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                    Console.WriteLine("Encoded Student IDs (in Descending Order)");

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                    manager.DisplayEncodedStudentIDs();

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                    break;

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                case 3:

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                    Console.WriteLine("First Name and Last Name (alphabetical)");

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                    manager.DisplayNamesAlphabetically();

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                    break;

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                case 4:

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                    Console.WriteLine("Student ID and Name");

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                    manager.DisplayStudentIDAndName();

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                    break;

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                case 0:

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                    Console.WriteLine("Thank You");

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                    break;

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                default:

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                    Console.WriteLine("Invalid action. Please enter a valid action.");

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                    break;

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            }

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        }

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    }

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}