Аквариум

using System;
using System.Collections.Generic;

namespace aquarius
{
    class Program
    {
        private const int CommandAddFish = 1;
        private const int CommandRemoveFish = 2;
        private const int CommandWait = 3;
        private const int CommandShowInfo = 4;
        private const int CommandExit = 5;

        static void Main(string[] args)
        {
            Aquarium aquarium = new Aquarium();
            bool isRunning = true;

            while (isRunning)
            {
                Console.Clear();
                Console.WriteLine($"{CommandAddFish} Добавить рыбу");
                Console.WriteLine($"{CommandRemoveFish} Извлечь рыбу");
                Console.WriteLine($"{CommandWait} Подождать");
                Console.WriteLine($"{CommandShowInfo} Показать информацию");
                Console.WriteLine($"{CommandExit} Выйти из программы");
                int userCommand = UserUtils.GetNumberFromUser();

                switch (userCommand)
                {
                    case CommandAddFish:
                        aquarium.AddFish();
                        break;

                    case CommandRemoveFish:
                        aquarium.RemoveFish();
                        break;

                    case CommandWait:
                        aquarium.Wait();
                        break;

                    case CommandShowInfo:
                        aquarium.ShowInfo();
                        break;

                    case CommandExit:
                        isRunning = false;
                        break;
                }
            }
        }
    }

    class UserUtils
    {
        public static int GetNumberFromUser()
        {
            string userInput;
            int userNumber;
            bool isNumber = false;

            do
            {
                userInput = Console.ReadLine();
                isNumber = int.TryParse(userInput, out userNumber);
            }
            while ((isNumber == false) || (userNumber < 0));

            return userNumber;
        }
    }

    class Aquarium
    {
        private List<Fish> _fish;

        public Aquarium()
        {
            _fish = new List<Fish>();
        }

        public void AddFish()
        {
            Console.WriteLine("Рыбку какого вида вы хотите добавить?");
            string species = Console.ReadLine();
            Console.WriteLine("Каков возраст рыбки?");
            int age = UserUtils.GetNumberFromUser();
            Fish newFish = new Fish(species, age);
            _fish.Add(newFish);
        }

        public void RemoveFish()
        {
            Console.WriteLine("Рыбку с каким индексом удалить?");
            int index = UserUtils.GetNumberFromUser() - 1;

            if (index < _fish.Count)
                _fish.RemoveAt(index);
            else
                Console.WriteLine("Рыбки с таким индексом в аквариуме нет");
        }

        public void Wait()
        {
            Console.WriteLine("Сколько времени подождать?");
            int waitingTime = UserUtils.GetNumberFromUser();

            foreach (Fish fish in _fish)
                fish.GrowOld(waitingTime);
        }

        public void ShowInfo()
        {
            for (int i = 0; i < _fish.Count; i++)
                Console.WriteLine($"{i + 1} {_fish[i].GetInfo()}");

            Console.ReadKey();
        }
    }

    class Fish
    {
        private int _maxLifetime = 100;
        private int _age;
        private int _maxAge;

        public Fish(string species, int age = 0)
        {
            Random random = new Random();
            _maxAge = random.Next(_maxLifetime);
            _age = 0;
            Species = species;
            GrowOld(age);
        }

        public bool IsAlive => _age <= _maxAge;
        public string Species { get; private set; }

        public void GrowOld(int time)
        {
            if (IsAlive == false)
                return;

            _age += time;
        }

        public string GetInfo()
        {
            string info;

            if (IsAlive)
                info = string.Format($"{Species}, возраст: {_age}");
            else
                info = string.Format($"{Species}, неживая");

            return info;
        }
    }
}