What is a linked list?

class node {
public:
	int data;
	node* link;
};

	node* head, *tail =new node();
	head = NULL, tail=NULL;

#include<iostream>
using namespace std;
class node {	//Creating a class of node
public:	
	node* link=NULL;
	int data=0;
};
class singly_link_list {  //This class stores the nodes of the list
public:
	node* head = NULL,*tail=NULL;
	void add_node(int p_data) { //function for adding new nodes into list
		node* temp_node=new node(); //temp_node stores the data temporary
		temp_node->data = p_data;
		temp_node->link = NULL;
		if (head == NULL) {    //Creating head
			head = temp_node;
			tail = temp_node;
		}
		else {                  //For insertion of all nodes other than head  
			
			tail->link = temp_node;
			tail = tail->link;
				
		}
	}
    	void display() {		//Function to print linked list
		
		node* temp_node = head;
		cout << "Link List : ";
		while (temp_node != NULL)  //Traversing each element and printing them
		{
			cout << temp_node->data << "  ";
			temp_node = temp_node->link;
		}
	}
};
//Driver code
int main()
{
	singly_link_list list;
	list.add_node(2); //Inserting head
	list.add_node(4); //Inserting other nodes
    list.add_node(6);
    list.display();   //printing list
}

void singly_link_list::search(int p_data) { //Function for searching
	node* temp = head;   //temporary node 
  int counter=0;
	while (temp != NULL) {  //traversing list
    
    counter++;
		if (temp->data == p_data) { //Value found
			cout << "\nValue has been found at position: " << counter<<endl;
			return;
		}
		else {						//Traverse next element
			temp = temp->link;
		}
	}
	cout << "\nValue doesn't exist in link list" << endl;
}
//Driver code
int main()
{
	singly_link_list list;
	list.add_node(2);
	list.add_node(4);
  	list.add_node(6);
  	list.display();
  	list.search(4);
}

#include<iostream>
using namespace std;
void singly_link_list::delete_node(int p_data){ //function for deletion
		node* current = new node(),*prev=new node(); //temporary nodes for keeping the track
		
		current = head;
		prev = tail;
		//Deleting Head
		
		if (p_data == head->data)
		{
			
			head = head->link;
			delete current;
			return;
		}
		while (current!=NULL) 
		{
			if (current->data == p_data)
				break;
			prev = current;
			current = current->link;
		}
		//Deleting Tail
		if (p_data == tail->data)
		{
			tail = prev;
			prev->link = NULL;
			delete current;
			return;
		}
		else if (current==NULL) //Element is not found
		{
			cout << endl << p_data << " doesn't exist in link list" << endl;
		}
		else					//Traversing next node
		{
			prev->link = current->link;
			delete current;
		}
}
//Driver code
int main()
{
	singly_link_list list;
	list.add_node(2);
	list.add_node(4);
  	list.add_node(6);
  	cout<<"Before Delete, ";
  	list.display();
  	list.delete_node(4);
  	cout<<"\nAfter Delete, ";
  	list.display();
}