Add linkedlist

[BhumikaMeghani]

Singly Linked List in C++ (Menu-Driven)

This program implements a singly linked list in C++ using a class-based approach.
It provides operations for insertion, deletion, display, and counting of nodes.
The program is menu-driven, allowing users to interactively perform operations.

Class: linkedlist

• Maintains a pointer start to the head node.
• Constructor: Initializes an empty list.
• addatbeg(int num): Insert at beginning.
• append(int num): Insert at end.
• addatloc(int loc, int num): Insert at a specific location.
• del(int num): Delete a node by value.
• display(): Print all nodes.
• count(): Return total number of nodes.
• Destructor: Frees allocated memory.

Menu Options

1. Add at beginning
2. Append at end
3. Add at a specific location
4. Delete a node
5. Display the list
6. Count nodes
7. Exit

This PR adds a complete implementation of singly linked list with a menu-driven interface.