namespace ConsoleApp6

{

    internal class Program

    {

        static void Main(string[] args)

        {

            Console.WriteLine("Start application...");

​

            PrintMenu();

            var exit = true;

​

            var courses = new List<Course>();

​

            var students = new List<Student>();

​

            do

            {

                var selectedMenu = Console.ReadLine();

                switch (selectedMenu)

                {

                    case "1":

                        Console.WriteLine("Enter multiple course names, split by ',':");

                        var courseNames = (Console.ReadLine() ?? "").Split(',');

                        foreach (var courseName in courseNames)

                        {

                            if (courses.Any(w => w.CourseName == courseName))

                            {

                                Console.WriteLine($"Course already exist: {courseName}");

                                continue;

                            }

                            courses.Add(new Course { CourseName = courseName });

                        }

​

                        Console.WriteLine($"Courses added: {string.Join(',', courses.Select(s => s.CourseName))}");

​

                        break;

                    case "2":

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

                        var student = new Student();

                        student.Id = Console.ReadLine();

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

                        student.Name = Console.ReadLine();

                        students.Add(student);

​

                        Console.WriteLine($"Student added: {student}");

                        break;

                    case "3":

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

                        var findStudentId = Console.ReadLine();

                        var findStudent = students.Find(w => w.Id == findStudentId);

                        if (findStudent == null)

                        {

                            Console.WriteLine($"Cannot find student with Id: {findStudentId}"); break;

                        }

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

                        var course = Console.ReadLine();

                        if (courses.All(w => w.CourseName != course))

                        {

                            Console.WriteLine($"Cannot find course: {course}");

                            break;

                        }

                        Console.WriteLine("Enter Student course score (score must be a number):");

                        var scoreInString = Console.ReadLine();

                        var score = double.Parse(scoreInString ?? "0");

​

                        if (findStudent.CourseResults.All(w => w.Course.CourseName != course))

                        {

                            findStudent.CourseResults.Add(new StudentCourseResult { Course = new Course { CourseName = course }, Score = score });

                        }

                        else

                            foreach (var studentCourse in findStudent.CourseResults)

                            {

                                if (studentCourse.Course.CourseName != course)

                                {

                                    Console.WriteLine($"Cannot find student course: {course}");

                                    break;

                                }

                                studentCourse.Score = score;

                            }

​

                        Console.WriteLine($"Student score: course: {course}, score: {findStudent.GetScoreByCourse(course)}");

​

                        break;

​

                    case "quit":

                        exit = false;

                        break;

                }

​

                if (selectedMenu != "quit")

                    PrintMenu();

            } while (exit);

        }

​

        static void PrintMenu()

        {

            Console.WriteLine("1. Set courses");

            Console.WriteLine("2. Add student");

            Console.WriteLine("3. Add student score");

            Console.WriteLine("4. Get student average score");

            Console.WriteLine("5. Get student with max average score");

            Console.WriteLine("100. Enter 'quit' to exit");

        }

    }

​

    public class Student

    {

        public Student()

        {

            CourseResults = new List<StudentCourseResult>();

        }

​

        public string Id { get; set; }

        public string Name { get; set; }

​

        public List<StudentCourseResult> CourseResults { get; set; }

​

        public override string ToString()

        {

            return $"Id: {Id}, Name: {Name}";

        }

​

        public double? GetScoreByCourse(string course)

        {

            return CourseResults.Where(w => w.Course.CourseName == course).Select(s => s.Score).FirstOrDefault();

        }

    }

​

    public class Course

    {

        public string CourseName { get; set; }

    }

​

    public class StudentCourseResult

    {

        public Course Course { get; set; }

        public double Score { get; set; }

    }

}