Explain the principle of operation of a linked list and its main features.

A linked list is a data structure consisting of nodes, where each node contains data and a reference to the next node (in a singly linked list) or to both the next and previous nodes (in a doubly linked list). Main features:

• Dynamic resizing without the need for contiguous memory allocation.
• Fast addition and removal of elements at the beginning or middle of the list.
• No direct access by index; access requires traversing the list sequentially.

Example of a singly linked list in C#:

class Node {
    public int Data;
    public Node Next;
}

class LinkedList {
    private Node head;

    public void AddFirst(int value) {
        Node newNode = new Node { Data = value, Next = head };
        head = newNode;
    }
}