4.1

using System;

namespace FifthProject
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] fio = new string[0];
            string[] post = new string[0];

            bool exit = false;

            while (!exit)
            {
                ShowMenu();
                switch (MenuInput())
                {
                    case '1':
                        Console.Write("Введите ФИО через пробел: ");
                        AddNewFile(ref fio, Console.ReadLine());
                        Console.Write("Введите пост: ");
                        AddNewFile(ref post, Console.ReadLine());
                        break;
                    case '2':
                        ShowAllFiles(fio, post);
                        Console.ReadKey();
                        break;
                    case '3':
                        Console.Write($"Выбрать досье: \n");
                        ShowAllFiles(fio, post);
                        SelectFileForDelete(ref fio,  ref post, ConvertToInt());
                        break;
                    case '4':
                        Console.Write("Введите фамилию: ");
                        FindFile(Console.ReadLine(), fio, post);
                        Console.ReadKey();
                        break;
                    case '5':
                        exit = true;
                        break;
                    default:
                        Console.WriteLine("Incorrect enter");
                        break;
                }

                Console.Clear();
            }
        }

        static void ShowMenu()
        {
            Console.WriteLine("\tMenu\n" +
                              "1. Add new file\n" +
                              "2. Show all files\n" +
                              "3. Delete file\n" +
                              "4. Find file\n" +
                              "5. Exit");
        }

        static char MenuInput()
        {
            char menuInput = Console.ReadKey(true).KeyChar;
            return menuInput;
        }

        static void AddNewFile(ref string[] arr, string str)
        {
            string[] tempArr = new string[arr.Length + 1];
            for (int i = 0; i < arr.Length; i++)
            {
                tempArr[i] = arr[i];
            }

            tempArr[tempArr.Length - 1] = str;

            arr = tempArr;
        }

        static void ShowAllFiles(string[] arr, string[] arr2)
        {
            if (arr.Length == 0)
            {
                Console.WriteLine("Empty list");
            }
            else
            {
                for (int i = 0; i < arr.Length; i++)
                {
                    Console.WriteLine($"{i + 1}. {arr[i]} - {arr2[i]}");
                }
            }
        }

        static void FindFile(string surname, string[] arr, string[] arr2)
        {
            for (int i = 0; i < arr.Length; i++)
            {
                string[] tempArr = arr[i].Split(' ');
                if (tempArr[1].ToLower() == surname.ToLower())
                {
                    Console.WriteLine($"{i + 1}. {arr[i]} - {arr2[i]}");
                }
            }
        }

        static void SelectFileForDelete(ref string[] arr, ref string[] arr2, int userInput)
        {

            DeleteFile(ref arr, userInput - 1);
            DeleteFile(ref arr2, userInput - 1);
        }

        static void DeleteFile(ref string[] arr, int userInput)
        {
            string[] tempArr = new string[arr.Length - 1];
            arr[userInput] = null;
            for (int i = 0; i < arr.Length - 1; i++)
            {
                if (arr[i] != null)
                {
                    tempArr[i] = arr[i];
                }
                else
                {
                    tempArr[i] = arr[i+1];
                }

            }

            arr = tempArr;
        }
        static int ConvertToInt()
        {
            Console.WriteLine("Enter file number");
            int output;
            bool enterIsCorrect = false;
            do
            {
                string input = Console.ReadLine();
                enterIsCorrect = int.TryParse(input, out output);
                if (!enterIsCorrect)
                {
                    Console.WriteLine("Error enter. Try again");
                }
            } while (!enterIsCorrect);

            return output;
        }
    }
}