# Doubly Linked List - Insert a new node at the end

In this method, a new node is inserted at the end of the doubly linked list. For example - if the given List is 10->20->30 and a new element 100 is added at the end, the List becomes 10->20->30->100.

Inserting a new node at the end of the doubly linked list is very easy. First, a new node with given element is created. It is then added at the end of the list by linking the last node to the new node.

The function push_back is created for this purpose. It is a 6-step process.

```void push_back(int newElement) {

//1. allocate node
Node* newNode = new Node();

//2. assign data element
newNode->data = newElement;

//3. assign null to the next and prev
//   of the new node
newNode->next = NULL;
newNode->prev = NULL;

//4. Check the list is empty or not,
//   if empty make the new node as head
} else {

//5. Else, traverse to the last node
while(temp->next != NULL)
temp = temp->next;

temp->next = newNode;
newNode->prev = temp;
}
}
```
```void push_back(struct Node** head_ref, int newElement) {

//1. allocate node
struct Node *newNode, *temp;
newNode = (struct Node*)malloc(sizeof(struct Node));

//2. assign data element
newNode->data = newElement;

//3. assign null to the next and prev
//   of the new node
newNode->next = NULL;
newNode->prev = NULL;

//4. Check the list is empty or not,
//   if empty make the new node as head
} else {

//5. Else, traverse to the last node
while(temp->next != NULL) {
temp = temp->next;
}

temp->next = newNode;
newNode->prev = temp;
}
}
```
```def push_back(self, newElement):

#1 & 2 & 3. allocate node, assign data element, assign
#          null to the next and prev of the new node
newNode = Node(newElement)

#4. Check the list is empty or not,
#   if empty make the new node as head
return
else:

#5. Else, traverse to the last node
while(temp.next != None):
temp = temp.next

temp.next = newNode
newNode.prev = temp
```
```void push_back(int newElement) {

//1. allocate node
Node newNode = new Node();

//2. assign data element
newNode.data = newElement;

//3. assign null to the next and prev
//   of the new node
newNode.next = null;
newNode.prev = null;

//4. Check the list is empty or not,
//   if empty make the new node as head
} else {

//5. Else, traverse to the last node
Node temp = new Node();
while(temp.next != null)
temp = temp.next;

temp.next = newNode;
newNode.prev = temp;
}
}
```
```public void push_back(int newElement) {

//1. allocate node
Node newNode = new Node();

//2. assign data element
newNode.data = newElement;

//3. assign null to the next and prev
//   of the new node
newNode.next = null;
newNode.prev = null;

//4. Check the list is empty or not,
//   if empty make the new node as head
} else {

//5. Else, traverse to the last node
Node temp = new Node();
while(temp.next != null)
temp = temp.next;

temp.next = newNode;
newNode.prev = temp;
}
}
```
```public function push_back(\$newElement) {

//1. allocate node
\$newNode = new Node();

//2. assign data element
\$newNode->data = \$newElement;

//3. assign null to the next and prev
//   of the new node
\$newNode->next = null;
\$newNode->prev = null;

//4. Check the list is empty or not,
//   if empty make the new node as head
} else {

//5. Else, traverse to the last node
\$temp = new Node();
while(\$temp->next != null) {
\$temp = \$temp->next;
}

\$temp->next = \$newNode;
\$newNode->prev = \$temp;
}
}
```

The below is a complete program that uses above discussed concept to insert new node at the end of the doubly linked list.

```#include <iostream>
using namespace std;

//node structure
struct Node {
int data;
Node* next;
Node* prev;
};

private:
public:
}

//Add new element at the end of the list
void push_back(int newElement) {
Node* newNode = new Node();
newNode->data = newElement;
newNode->next = NULL;
newNode->prev = NULL;
} else {
while(temp->next != NULL)
temp = temp->next;
temp->next = newNode;
newNode->prev = temp;
}
}

//display the content of the list
void PrintList() {
if(temp != NULL) {
cout<<"The list contains: ";
while(temp != NULL) {
cout<<temp->data<<" ";
temp = temp->next;
}
cout<<"\n";
} else {
cout<<"The list is empty.\n";
}
}
};

// test the code
int main() {

//Add three elements at the end of the list.
MyList.push_back(10);
MyList.push_back(20);
MyList.push_back(30);
MyList.PrintList();

return 0;
}
```

The above code will give the following output:

```The list contains: 10 20 30
```
```#include <stdio.h>
#include <stdlib.h>

//node structure
struct Node {
int data;
struct Node* next;
struct Node* prev;
};

//Add new element at the end of the list
void push_back(struct Node** head_ref, int newElement) {
struct Node *newNode, *temp;
newNode = (struct Node*)malloc(sizeof(struct Node));
newNode->data = newElement;
newNode->next = NULL;
newNode->prev = NULL;
} else {
while(temp->next != NULL) {
temp = temp->next;
}
temp->next = newNode;
newNode->prev = temp;
}
}

//display the content of the list
printf("The list contains: ");
while (temp != NULL) {
printf("%i ",temp->data);
temp = temp->next;
}
printf("\n");
} else {
printf("The list is empty.\n");
}
}

// test the code
int main() {
struct Node* MyList = NULL;

//Add three elements at the end of the list.
push_back(&MyList, 10);
push_back(&MyList, 20);
push_back(&MyList, 30);
PrintList(MyList);

return 0;
}
```

The above code will give the following output:

```The list contains: 10 20 30
```
```# node structure
class Node:
def __init__(self, data):
self.data = data
self.next = None
self.prev = None

def __init__(self):

#Add new element at the end of the list
def push_back(self, newElement):
newNode = Node(newElement)
return
else:
while(temp.next != None):
temp = temp.next
temp.next = newNode
newNode.prev = temp

#display the content of the list
def PrintList(self):
if(temp != None):
print("The list contains:", end=" ")
while (temp != None):
print(temp.data, end=" ")
temp = temp.next
print()
else:
print("The list is empty.")

# test the code

#Add three elements at the end of the list.
MyList.push_back(10)
MyList.push_back(20)
MyList.push_back(30)
MyList.PrintList()
```

The above code will give the following output:

```The list contains: 10 20 30
```
```//node structure
class Node {
int data;
Node next;
Node prev;
};

}

//Add new element at the end of the list
void push_back(int newElement) {
Node newNode = new Node();
newNode.data = newElement;
newNode.next = null;
newNode.prev = null;
} else {
Node temp = new Node();
while(temp.next != null)
temp = temp.next;
temp.next = newNode;
newNode.prev = temp;
}
}

//display the content of the list
void PrintList() {
Node temp = new Node();
if(temp != null) {
System.out.print("The list contains: ");
while(temp != null) {
System.out.print(temp.data + " ");
temp = temp.next;
}
System.out.println();
} else {
System.out.println("The list is empty.");
}
}
};

// test the code
public class Implementation {
public static void main(String[] args) {

//Add three elements at the end of the list.
MyList.push_back(10);
MyList.push_back(20);
MyList.push_back(30);
MyList.PrintList();
}
}
```

The above code will give the following output:

```The list contains: 10 20 30
```
```using System;

//node structure
class Node {
public int data;
public Node next;
public Node prev;
};

}

//Add new element at the end of the list
public void push_back(int newElement) {
Node newNode = new Node();
newNode.data = newElement;
newNode.next = null;
newNode.prev = null;
} else {
Node temp = new Node();
while(temp.next != null)
temp = temp.next;
temp.next = newNode;
newNode.prev = temp;
}
}

//display the content of the list
public void PrintList() {
Node temp = new Node();
if(temp != null) {
Console.Write("The list contains: ");
while(temp != null) {
Console.Write(temp.data + " ");
temp = temp.next;
}
Console.WriteLine();
} else {
Console.WriteLine("The list is empty.");
}
}
};

// test the code
class Implementation {
static void Main(string[] args) {

//Add three elements at the end of the list.
MyList.push_back(10);
MyList.push_back(20);
MyList.push_back(30);
MyList.PrintList();
}
}
```

The above code will give the following output:

```The list contains: 10 20 30
```
```<?php
//node structure
class Node {
public \$data;
public \$next;
public \$prev;
}

public function __construct(){
}

//Add new element at the end of the list
public function push_back(\$newElement) {
\$newNode = new Node();
\$newNode->data = \$newElement;
\$newNode->next = null;
\$newNode->prev = null;
} else {
\$temp = new Node();
while(\$temp->next != null) {
\$temp = \$temp->next;
}
\$temp->next = \$newNode;
\$newNode->prev = \$temp;
}
}

//display the content of the list
public function PrintList() {
\$temp = new Node();
if(\$temp != null) {
echo "The list contains: ";
while(\$temp != null) {
echo \$temp->data." ";
\$temp = \$temp->next;
}
echo "\n";
} else {
echo "The list is empty.\n";
}
}
};

// test the code

//Add three elements at the end of the list.
\$MyList->push_back(10);
\$MyList->push_back(20);
\$MyList->push_back(30);
\$MyList->PrintList();
?>
```

The above code will give the following output:

```The list contains: 10 20 30
```

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