Добавьте файлы проекта.

CollectionUtils.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq; 
+using System.Text;
+
+namespace First_week
+{
+    internal static class CollectionUtils
+    {
+        public static bool IsNullOrEmpty<T>(this IEnumerable<T> collection)
+        {
+            return collection == null || !collection.Any();
+        }
+        public static List<T> ToSafeList<T>(this IEnumerable<T> collection)
+        {
+            return collection?.ToList() ?? new List<T>();
+        }
+
+        public static void Shuffle<T>(this IList<T> list)
+        {
+            if (list == null)
+                return;
+
+            Random rng = new Random();
+            int n = list.Count;
+            while (n > 1)
+            {
+                n--;
+                int k = rng.Next(n + 1);
+                T value = list[k];
+                list[k] = list[n];
+                list[n] = value;
+            }
+        }
+    }
+}

First week.slnx

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+<Solution>
+  <Project Path="../ContactsApp/ContactsApp.csproj" Id="a2bc9165-c669-4d35-8a64-2c0bbeff9da4" />
+  <Project Path="UtilityLibrary.csproj" />
+</Solution>

StringUtils.cs

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+namespace First_week
+{
+    internal class StringUtils
+    {
+        public static bool IsPalindrome(string s)
+        {
+            if (string.IsNullOrEmpty(s))
+                return false;
+
+            string cleaned = new string(s.Where(c => char.IsLetterOrDigit(c)).ToArray()).ToLower();
+            string reversed = new string(cleaned.Reverse().ToArray());
+
+            return cleaned == reversed;
+        }
+
+        public static string ReverseWords(string sentence)
+        {
+            if (string.IsNullOrEmpty(sentence))
+                return sentence;
+
+            var words = sentence.Split(' ');
+            var reversedWords = words.Select(word => new string(word.Reverse().ToArray()));
+
+            return string.Join(" ", reversedWords);
+        }
+
+        public static string RemovePunctuation(string s)
+        {
+            if (string.IsNullOrEmpty(s))
+                return s;
+
+            return new string(s.Where(c => !char.IsPunctuation(c)).ToArray());
+        }
+
+        public static bool IsAlphaNumeric(string s)
+        {
+            if (string.IsNullOrEmpty(s))
+                return false;
+
+            return s.All(char.IsLetterOrDigit);
+        }
+    }
+}

Test.cs

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+using System.Net.Mail;
+using First_week;
+
+User nekit = new User("Nikita", "Polyanin", new MailAddress("polyanin@mail.ru"), new DateOnly(2004, 12, 8));
+Console.WriteLine(nekit.GetFullName());
+
+nekit.UpdateEmail(new MailAddress("lox@mail.ru"));
+Console.WriteLine(nekit.Email);
+
+nekit.UpdateDate(new DateOnly(2024,12, 8));
+Console.WriteLine(nekit.Date);
+
+CollectionUtils.Shuffle()

User.cs

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+using System;
+using System.Collections.Generic;
+using System.Dynamic;
+using System.Net.Mail;
+using System.Runtime.CompilerServices;
+using System.Text;
+
+namespace First_week
+{
+    internal class User
+    {
+        public Guid Id { get; }
+        public string Name { get; private set; }
+        public string Surname { get; private set; }
+        public MailAddress? Email { get; private set; }
+        public DateOnly Date { get; private set; }
+        public bool IsActive { get; private set; }
+
+        public User(string name, string surname, MailAddress email, DateOnly date)
+        {
+            if (name == null || name.Length > 100)
+                throw new Exception("Incorrect name");
+
+            if (surname == null || surname.Length > 100)
+                throw new Exception("Incorrect surname");
+
+            if (date.CompareTo(DateOnly.FromDateTime(DateTime.Now)) > 0)
+                throw new Exception("Incorrect birthdate");
+
+            Id = Guid.NewGuid();
+            Name = name;
+            Surname = surname;
+            Email = email;
+            Date = date;
+            IsActive = true;
+        }
+
+        public string GetFullName()
+        {
+            return ($"{Surname} {Name}");
+        }
+
+        public void UpdateEmail(MailAddress newMail)
+        {
+            Email = newMail;
+        }
+
+        public void UpdateDate(DateOnly date)
+        {
+            if (date.CompareTo(DateOnly.FromDateTime(DateTime.Now)) > 0)
+                throw new Exception("Wrong date");
+
+            Date = date;
+        }
+
+        public void Deactivate()
+        {
+            IsActive = false;
+        }
+    }
+}

UserManager.cs

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+using Microsoft.Win32;
+using System;
+using System.Collections.Generic;
+using System.Net.Mail;
+using System.Text;
+
+namespace First_week
+{
+    internal class UserManager
+    {
+        public List <User> Registory = new();
+
+        public void AddUser(User user)
+        {
+            CheckUniqe(user);
+            Registory.Add(user); 
+        }
+
+        public void RemoveUser(Guid id)
+        {
+            User? user = Registory.Find(x => x.Id == id);
+            if (user == null)
+                return;
+
+            Registory.Remove(user);
+        }
+
+        public User Find(Guid id)
+        {
+            User? user = Registory.Find(x => x.Id == id);
+            if (user == null)
+                throw new Exception("Not found");   
+
+            return user;
+        }
+
+        public User Find(MailAddress email)
+        {
+            User? user = Registory.Find(x => x.Email == email);
+            if (user == null)
+                throw new Exception("Not found");
+
+            return user;
+        }
+
+        private void CheckUniqe(User user)
+        {
+            if (Registory.FirstOrDefault(x => x.Equals(user)) != null)
+                throw new Exception("Such a user already exists");
+        }
+
+        public void Show()
+        {
+            foreach (var user in Registory)
+            {
+                Console.WriteLine($"{user.GetFullName} {user.Id}");
+            }
+        }
+    }
+}

UtilityLibrary.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <RootNamespace>First_week</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>