diff --git a/05. Arrays/Reverse an array.cpp b/05. Arrays/Reverse an array.cpp
index e4aba831..bc48ce7f 100644
--- a/05. Arrays/Reverse an array.cpp	
+++ b/05. Arrays/Reverse an array.cpp	
@@ -1,5 +1,27 @@
 #include <iostream>
 using namespace std;
+
+//fun reverse array using while loop -start here
+void reverse_array(int arr[],int n)
+{
+	int start=0;
+	int end=n-1;
+	while(start<end)
+	{
+		int temp=arr[start];
+		arr[start]=arr[end];
+		arr[end]=temp;
+	}
+	cout<<"array is reversed using while loop:"<<endl;
+	//out put of the array
+	for(int i=0;i<n;i++)
+	{
+		cout<<arr[i]<< " ";
+	}
+	cout<<endl;
+	cout<<"array reversed using for loop"<<endl;
+}
+/*--------------------------------end here--------------------------------*/
 int main() {
   
   //number of test cases
@@ -18,6 +40,7 @@ int main() {
          //Input array elements
 	        cin>>A[i];
 	    }
+		reverse_array(A,n);
 	    for(int begin=0;begin<(n/2);begin++)
 	    {
      
diff --git a/11. Linked List/doubly_linked_list.cpp b/11. Linked List/doubly_linked_list.cpp
index e6c2a89c..b0360275 100644
--- a/11. Linked List/doubly_linked_list.cpp	
+++ b/11. Linked List/doubly_linked_list.cpp	
@@ -1,89 +1,258 @@
-#include<iostream>
+#include <iostream>
 using namespace std;
-
-class Node
-{
-    public:
-    Node *back;
-    int data;
-    Node *next;
+  
+// A doubly linked list node
+struct Node {
+   int data;
+   struct Node* next;
+   struct Node* prev;
 };
-
-Node *first=NULL;
-
-void create_dll(int A[],int n)
+  
+//inserts node at the front of the list
+void insert_front(struct Node** head, int new_data)
 {
-     first=new Node;
-     first->back=NULL;
-     first->data=A[0];
-     first->next=NULL;
-
-     Node *current_ptr=first;
-
-     for(int i=1;i<n;i++)
-     {
-         Node *temp=new Node;
-         temp->data=A[i];
-
-         temp->back=current_ptr;
-         temp->next=NULL;
-         current_ptr->next=temp;
-         current_ptr=temp;
-     }
+   //allocate memory for New node
+   struct Node* newNode = new Node;
+  
+   //assign data to new node
+   newNode->data = new_data;
+  
+   //new node is head and previous is null, since we are adding at the front
+   newNode->next = (*head);
+   newNode->prev = NULL;
+  
+   //previous of head is new node
+   if ((*head) != NULL)
+   (*head)->prev = newNode;
+  
+   //head points to new node
+   (*head) = newNode;
 }
-
-
-void Display()
+/* Given a node as prev_node, insert a new node after the given node */
+void insert_After(struct Node* prev_node, int new_data)
+{
+   //check if prev node is null
+   if (prev_node == NULL) {
+   cout<<"Previous node is required , it cannot be NULL";
+   return;
+}
+   //allocate memory for new node
+   struct Node* newNode = new Node;
+  
+   //assign data to new node
+   newNode->data = new_data;
+  
+   //set next of newnode to next of prev node
+   newNode->next = prev_node->next;
+  
+   //set next of prev node to newnode
+   prev_node->next = newNode;
+  
+   //now set prev of newnode to prev node
+   newNode->prev = prev_node;
+  
+   //set prev of new node's next to newnode
+   if (newNode->next != NULL)
+   newNode->next->prev = newNode;
+}
+  
+//insert a new node at the end of the list
+void insert_end(struct Node** head, int new_data)
 {
-   Node *ptr=first;
-   while(ptr)
-   {
-       cout<<"<-"<<ptr->data<<"->";
-       ptr=ptr->next;
+   //allocate memory for node
+   struct Node* newNode = new Node;
+  
+   struct Node* last = *head; //set last node value to head
+  
+   //set data for new node
+   newNode->data = new_data;
+  
+   //new node is the last node , so set next of new node to null
+   newNode->next = NULL;
+  
+   //check if list is empty, if yes make new node the head of list
+   if (*head == NULL) {
+   newNode->prev = NULL;
+   *head = newNode;
+    return;
+}
+  
+//otherwise traverse the list to go to last node
+while (last->next != NULL)
+last = last->next;
+  
+//set next of last to new node
+last->next = newNode;
+  
+//set last to prev of new node
+newNode->prev = last;
+return;
+}
+  
+// This function prints contents of linked list starting from the given node
+void displayList(struct Node* node) {
+   struct Node* last;
+  
+   while (node != NULL) {
+      cout<<node->data<<"<==>";
+      last = node;
+      node = node->next;
+   }
+   if(node == NULL)
+   cout<<"NULL";
    }
-   cout<<endl;
+  
+//main program
+int main() {
+   /* Start with the empty list */
+   struct Node* head = NULL;
+  
+   // Insert 40 as last node
+   insert_end(&head, 40);
+  
+   // insert 20 at the head
+   insert_front(&head, 20);
+  
+   // Insert 10 at the beginning.
+   insert_front(&head, 10);
+  
+   // Insert 50 at the end.
+   insert_end(&head, 50);
+  
+   // Insert 30, after 20.
+   insert_After(head->next, 30);
+  
+   cout<<"Doubly linked list is as follows: "<<endl;
+   displayList(head);
+   return 0;
 }
+Output:
 
+Doubly linked list is as follows:
 
-int deletion(int pos)
-{
-    int x=-1;
-    if(pos==1)
-    {
-        Node *ptr=first;
-        first=first->next;
-        x=ptr->data;
-        delete(ptr);
-        first->back=NULL;
-    }
-
-    else
-    {
-        Node *q=first;
-        for(int i=0;i<pos-1;i++)
-        {
-            q=q->next;
-        }
-        if(q!=NULL)
-        {
-            q->back->next=q->next;
-            q->next->back=q->back;
+10<==>20<==>30<==>40<==>50<==>NULL
 
-            x=q->data;
-            delete(q);
-        }
-    }
-    return x;
-}
+The above program constructs a doubly linked list by inserting the nodes using three insertion methods i.e. inserting the node at the front, inserting the node at the end and inserting the node after the given node.
 
+Next, we demonstrate the same operation as a Java implementation.
 
-int main()
+// Java Class for Doubly Linked List
+class Doubly_linkedList {
+   Node head; // list head
+  
+    /* Doubly Linked list Node*/
+   class Node {
+      int data;
+      Node prev;
+      Node next;
+  
+      //create a new node using constructor
+      Node(int d) { data = d; }
+   }
+  
+// insert a node at the front of the list
+public void insert_front(int new_data)
 {
-    int A[]={1,2,3,4,5};
-    int n ;
-    n= sizeof(A)/sizeof(A[0]);
-    create_dll(A,n);
-    Display();
-    cout<<deletion(3)<<endl;
-    Display();
-}
\ No newline at end of file
+   /* 1. allocate node
+   * 2. put in the data */
+   Node new_Node = new Node(new_data);
+  
+   /* 3. Make next of new node as head and previous as NULL */
+   new_Node.next = head;
+   new_Node.prev = null;
+  
+   /* 4. change prev of head node to new node */
+   if (head != null)
+   head.prev = new_Node;
+  
+   /* 5. move the head to point to the new node */
+   head = new_Node;
+}
+//insert a node after the given prev node
+public void Insert_After(Node prev_Node, int new_data)
+{
+   //check that prev node is not null
+   if (prev_Node == null) {
+   System.out.println("The previous node is required,it cannot be NULL ");
+   return;
+}
+  
+   //allocate new node and set it to data
+   Node newNode = new Node(new_data);
+  
+   //set next of newNode as next of prev node
+   newNode.next = prev_Node.next;
+  
+   //set new node to next of prev node
+   prev_Node.next = newNode;
+  
+   //set prev of newNode as prev node
+   newNode.prev = prev_Node;
+  
+   //set prev of new node's next to newnode
+   if (newNode.next != null)
+   newNode.next.prev = newNode;
+}
+  
+// Add a node at the end of the list
+void insert_end(int new_data)   {
+   //allocate the node and set the data
+   Node newNode = new Node(new_data);
+   Node last = head; //set last as the head
+   //set next of new node to null since its the last node
+   newNode.next = null;
+  
+   //set new node as head if the list is null
+   if (head == null) {
+      newNode.prev = null;
+      head = newNode;
+      return;
+   }
+   //if list is not null then traverse it till the last node and set last next to last
+   while (last.next != null)
+   last = last.next;
+  
+   last.next = newNode;           //set last next to new node
+  
+   newNode.prev = last;           //set last as prev of new node
+}
+// display the contents of linked list starting from the given node
+public void displaylist(Node node)
+{
+   Node last = null;
+   while (node != null) {
+      System.out.print(node.data + "<==>");
+      last = node;
+      node = node.next;
+   }
+   if(node == null)
+   System.out.print("null");
+   System.out.println();
+  
+   }
+}
+class Main{
+   public static void main(String[] args)
+      {
+      /* Start with the empty list */
+      Doubly_linkedList dll = new Doubly_linkedList();
+  
+      // Insert 40.
+      dll.insert_end(40);
+  
+      // Insert 20 at the beginning.
+      dll.insert_front(20);
+  
+      // Insert 10 at the beginning.
+      dll.insert_front(10);
+  
+      // Insert 50 at the end.
+      dll.insert_end(50);
+  
+      // Insert 30, after 20.
+      dll.Insert_After(dll.head.next, 30);
+  
+      System.out.println("Doubly linked list created is as follows: ");
+      dll.displaylist(dll.head);
+      }
+}
diff --git a/stock_buy_and_sell_variations/stock_first_type b/stock_buy_and_sell_variations/stock_first_type
new file mode 100644
index 00000000..e69de29b