update

Server App/Program.cs

@@ -0,0 +1,50 @@
+using System.Net;
+using System.Net.Sockets;
+using System.Text;
+
+class Server
+{
+    static void Main()
+    {
+        TcpListener server = new TcpListener(IPAddress.Any, 8888);
+
+        try
+        {
+            server.Start();
+            Console.WriteLine("Сервер запущен");
+
+            while (true)
+            {
+                TcpClient client = server.AcceptTcpClient();
+                NetworkStream stream = client.GetStream();
+
+                byte[] buffer = new byte[1024];
+                int bytes = stream.Read(buffer, 0, buffer.Length);
+
+                string text = Encoding.UTF8.GetString(buffer, 0, bytes);
+                Console.WriteLine($"Получено: {text}");
+
+                string response = $"OK: {StrProc(text)}";
+                byte[] data = Encoding.UTF8.GetBytes(response);
+                stream.Write(data, 0, data.Length);
+
+                stream.Close();
+                client.Close();
+            }
+        }
+        catch (Exception e)
+        {
+            Console.WriteLine($"Ошибка: {e.Message}");
+        }
+        finally
+        {
+            server.Stop();
+        }
+    }
+
+    //18 вариант
+    private static string StrProc(string str)
+    {
+        return str.Replace('y', 'o');
+    }
+}

Server App/Server App.csproj

@@ -0,0 +1,11 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <RootNamespace>Server_App</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>