This program implements a doubly linked list to print the list forward and backward. It defines a Node struct with data, next and prev pointers. It inserts nodes at the head of the list using InsertAtHead() and prints the list forward using Print() and backward using ReversePrint(). It initially inserts two nodes and prints the list both ways. It then inserts three more nodes at the head and prints the list again forward and backward.

1. 4. Example Programs
Compile these C++programsand figure outwhatthe outputis andwhyis it appearedlike that.
4.1 Example Program 1: Add/Insertnode infront / at the beginningof a linkedlist
#include <cstdlib>
#include <iostream>
using namespace std;
struct Node
{
int data;
Node* next;
};
Node* head;
void Insert(int x)
{
Node* temp = new Node();
temp->data = x;
temp->next = head;
head = temp;
}
void Print()
{
Node* temp = head;
cout<<"List is : ";
while(temp!=NULL)
{
cout<<temp->data<<"t";
temp=temp->next;
}
cout<<endl;
}
int main()
{
head=NULL;
cout<<"How many no?n";
int n,i,x;
cin>>n;
for(i=0;i<n;i++)
{
cout<<"Enter no: n";
cin>>x;
Insert(x);
Print();
}

2. }
Output:
Comment:
Thisprogram receivesuserinputandliststheminorderof newestfirstbyreplacingthe mostrecent
inputwithlatestinputanddisplayingthem

3. 4.2 Example Program 2 : Add/Insert node at nth positionin the linkedlist.
#include <cstdlib>
#include <iostream>
using namespace std;
// A linked list Node
struct Node {
int data;
struct Node* next;
};
// Size of linked list
int size = 0;
// function to create and return a Node
Node* getNode(int data)
{
// allocating space
Node* newNode = new Node();
// inserting the required data
newNode->data = data;
newNode->next = NULL;
return newNode;
}
// function to insert a Node at required position
void insertPos(Node** current, int pos, int data)
{
// This condition to check whether the
// position given is valid or not.
if (pos < 1 || pos > size + 1)
cout << "Invalid position!" << endl;
else {
// Keep looping until the pos is zero
while (pos--) {
if (pos == 0) {
// adding Node at required position
Node* temp = getNode(data);
// Making the new Node to point to
// the old Node at the same position
temp->next = *current;
// Changing the pointer of the Node previous
// to the old Node to point to the new Node
*current = temp;
}
else
// Assign double pointer variable to point to the
// pointer pointing to the address of next Node

4. current = &(*current)->next;
}
size++;
}
}
// This function prints contents
// of the linked list
void printList(struct Node* head)
{
while (head != NULL) {
cout << " " << head->data;
head = head->next;
}
cout << endl;
}
// Driver Code
int main()
{
// Creating the list 3->5->8->10
Node* head = NULL;
head = getNode(3);
head->next = getNode(5);
head->next->next = getNode(8);
head->next->next->next = getNode(10);
size = 4;
cout << "Linked list before insertion: ";
printList(head);
int data = 12, pos = 3;
insertPos(&head, pos, data);
cout << "Linked list after first insertion is: ";
printList(head);
// front of the linked list
data = 1, pos = 1;
insertPos(&head, pos, data);
cout << "Linked list after second insertion is: ";
printList(head);
// insertion at end of the linked list
data = 15, pos = 7;
insertPos(&head, pos, data);
cout << "Linked list after third insertion is: ";
printList(head);
return 0;
}

5. Output:
Comment:
ThisProgram insertsanumberintoa premade listat a specificposition(1st
,3rd
,7th
) usingspecificvalues
to representthem(dataandpos)

6. 4.3 Example Program 3 : Delete node at nth positioninthe linked list
#include <cstdlib>
#include <iostream>
using namespace std;
struct Node
{
int data;
Node* next;
};
Node* head;
void Insert(int x)
{
Node* temp = new Node();
temp->data = x;
temp->next = head;
head = temp;
}
//temp1 points to (n-1)th node
void Delete (int n)
{
Node* temp1=head;
if(n==1)
{
head=temp1->next;
free(temp1);
return;
}
int i;
for(i=0;i<n-2;i++)
{
temp1=temp1->next;
}
Node* temp2=temp1->next;
temp1->next=temp2->next;
free(temp2);
}
void Print()
{
Node* temp = head;
cout<<"Linked List is : ";
while(temp!=NULL)
{
cout<<temp->data<<"t";
temp=temp->next;

7. }
cout<<endl;
}
int main()
{
head=NULL;
Insert(24);
Insert(38);
Insert(14);
Insert(59);
Print();
Delete(2);
Print();
}
Output:
Comment:
Thisprogram deletesanumberfroma predeterminedlinkedlistusingvoid(Delete) call

8. 4.4 Example Program 4 : Reverse a linkedlist.
#include <cstdlib>
#include <iostream>
using namespace std;
struct Node
{
int data;
Node* next;
};
Node* Insert(Node* head,int x)
{
Node* temp = new Node();
temp->data = x;
temp->next = head;
head = temp;
return head;
}
Node* Reverse (Node* head)
{
Node *c,*p,*n;
c=head;
p=NULL;
while(c!=NULL)
{
n=c->next;
c->next=p;
p=c;
c=n;
}
head=p;
return head;
}
void Print(Node* head)
{
cout<<"Linked List is : ";
while(head!=NULL)
{
cout<<head->data<<"t";
head=head->next;
}
cout<<endl;
}
int main()
{

9. Node* head=NULL;
head=Insert(head,2);
head=Insert(head,3);
head=Insert(head,4);
head=Insert(head,5);
Print(head);
head=Reverse(head);
Print(head);
}
Output:
Comment:
Thisprogram reversesthe orderof a predeterminedlinkedlistthrough head=Reverse(head) command
thisrearrangesthe “head”or order of numberpositionsstartingfromlasttofirst

10. 4.5 Example Program 5 : Print a linkedListForward and Backward using recursion.
#include <cstdlib>
#include <iostream>
using namespace std;
struct Node
{
int data;
Node* next;
};
Node* Insert(Node* head,int data)
{
Node* temp = new Node();
temp->data = data;
temp->next = NULL;
if (head==NULL)head=temp;
else
{
Node* temp1=head;
while (temp1->next != NULL) temp1=temp1->next;
temp1->next=temp;
}
return head;
}
void Print(Node* p)
{
if(p==NULL) return; //exit condition
cout<<p->data<<" "; //print data in node
Print(p->next); //recursive function
}
void ReversePrint (Node* p)
{
if(p==NULL) return;
ReversePrint(p->next);
cout<<p->data<<" ";
}
int main()
{
Node* head=NULL;
head=Insert(head,2);
head=Insert(head,3);
head=Insert(head,4);
head=Insert(head,5);
cout<<"nPrint forward : ";
Print(head);

11. cout<<"nnPrint Reverse/Backward : ";
ReversePrint(head);
cout<<endl<<endl;
}
Output:
Comment:
Thisprogram issimilartoExample program4.4 whereasthe linkedlistisprinted,reversed,andprinted
againto displaythe listinitsinitial andreversedform

12. 4.6 Example Program 6 : Implementationdoublylinkedlist– to print forward and backward
#include <cstdlib>
#include <iostream>
using namespace std;
struct Node
{
int data;
Node* next;
Node* prev;
};
Node* head;
Node* GetNewNode(int x)
{
Node* newNode = new Node();
newNode->data=x;
newNode->next=NULL;
newNode->prev=NULL;
return newNode;
}
void InsertAtHead(int x)
{
Node* newNode = GetNewNode(x);
if(head==NULL)
{
head=newNode;
return;
}
head->prev=newNode;
newNode->next=head;
head=newNode;
}
void Print()
{
Node* temp = head;
cout<<"Forward: ";
while(temp!=NULL)
{
cout<<temp->data<<"t";
temp=temp->next;
}
cout<<endl;
}
void ReversePrint()
{

13. Node* temp = head;
if(temp==NULL)return;
while(temp->next!=NULL)
{
temp=temp->next;
}
cout<<"Reverse: ";
while(temp!=NULL)
{
cout<<temp->data<<"t";
temp=temp->prev;
}
cout<<endl;
}
int main()
{
head=NULL;
InsertAtHead(22);
InsertAtHead(71);
Print();
ReversePrint();
InsertAtHead(38);
InsertAtHead(53);
InsertAtHead(75);
Print();
ReversePrint();
}
Output:
Comment:
Thisprogram isa combinationof Example program4.4and 4.5 but utilizestwolinkedlistsbyadding
another3 nodesafterthe initial forwardandreverse display