Initial data commit

Task/Doubly-linked-list-Definition/C-sharp/doubly-linked-list-definition.cs

@@ -0,0 +1,26 @@
+using System.Collections.Generic;
+
+class Program
+{
+    static void Main(string[] args)
+    {
+        LinkedList<string> list = new LinkedList<string>();
+        list.AddFirst(".AddFirst() adds at the head.");
+        list.AddLast(".AddLast() adds at the tail.");
+        LinkedListNode<string> head = list.Find(".AddFirst() adds at the head.");
+        list.AddAfter(head, ".AddAfter() adds after a specified node.");
+        LinkedListNode<string> tail = list.Find(".AddLast() adds at the tail.");
+        list.AddBefore(tail, "Betcha can't guess what .AddBefore() does.");
+
+        System.Console.WriteLine("Forward:");
+        foreach (string nodeValue in list) { System.Console.WriteLine(nodeValue); }
+
+        System.Console.WriteLine("\nBackward:");
+        LinkedListNode<string> current = tail;
+        while (current != null)
+        {
+            System.Console.WriteLine(current.Value);
+            current = current.Previous;
+        }
+    }
+}