diff --git a/src/Chapter_04_Queues/CircularLinkedListUDF.c b/src/Chapter_04_Queues/CircularLinkedListUDF.c
new file mode 100644
index 0000000..b1d914f
--- /dev/null
+++ b/src/Chapter_04_Queues/CircularLinkedListUDF.c
@@ -0,0 +1,188 @@
+#include<stdio.h>
+#include<stdlib.h>
+struct node
+{
+int data;
+struct node *next;
+};
+typedef struct node NODE;
+NODE *LLnode,*head,*temp,*prev,*second;
+NODE* insert_at_front(NODE *);
+NODE* insert_at_end(NODE *);
+NODE* delete_at_front(NODE *);
+NODE* delete_at_end(NODE *);
+void display(NODE *);
+
+
+main()
+{
+int ch;
+head=NULL;
+
+do
+{
+    printf("1--insert node at the front\n");
+    printf("2--insert node at the end\n");
+    printf("3--delete a node at the front\n");
+    printf("4--delete a node at the end\n");
+    printf("5--display the linked list\n");
+   printf("6--close the program\n");
+
+printf("enter your choice\n");
+scanf("%d",&ch);
+switch(ch)
+{
+case 1:  head=insert_at_front(head);
+
+                break;
+case 2: head=insert_at_end(head);
+
+                break;
+case 3:head=delete_at_front(head);
+
+                 break;
+case 4: head=delete_at_end(head);
+
+                 break;
+case 5:   display(head);
+                break;
+case 6: exit(0);break;
+default:printf("Invalid choice\n");
+                break;
+}
+}while(ch!=6);
+
+
+}
+NODE* insert_at_front(NODE *head)
+{
+    LLnode=(NODE *)malloc(sizeof(NODE));
+                printf("enter the data\n");
+                scanf("%d",&LLnode->data);
+
+                if(head==NULL)
+                {
+                    head=LLnode;
+                    head->next=head;
+                }
+                else
+                {
+                  temp=head;
+                  while(temp->next!=head)
+            {
+            temp=temp->next;
+            }
+                  LLnode->next=head;
+                  head=LLnode;
+            temp->next=head;
+                }
+        return(head);
+
+}
+
+NODE* insert_at_end(NODE *head)
+{
+    LLnode=(NODE *)malloc(sizeof(NODE));
+                printf("enter the data\n");
+                scanf("%d",&LLnode->data);
+
+                if(head==NULL)
+                {
+                    head=LLnode;
+            head->next=head;
+                }
+                else
+                {
+                    temp=head;
+                    while(temp->next!=head)
+                    {
+                        temp=temp->next;
+                    }
+                    temp->next=LLnode;
+            LLnode->next=head;
+                }
+        return(head);
+
+}
+
+NODE* delete_at_front(NODE *head)
+{
+    if(head==NULL)
+                {
+                    printf("Linked list is empty...cant delete a node\n");
+                 }
+                 else
+                 {
+
+                    if(head->next==head)
+            {
+            printf("node deleted=%d\n",head->data);
+            free(head);
+            head=NULL;
+            }
+            else
+            {
+            second=head->next;
+            temp=head;
+            while(temp->next!=head)
+            {
+            temp=temp->next;
+            }
+             printf("node deleted=%d\n",head->data);
+            free(head);
+            head=second;
+            temp->next=head;
+            }
+
+                 }
+                return(head);
+}
+
+NODE*  delete_at_end(NODE *head)
+{
+    if(head==NULL)
+                {
+                    printf("Linked list is empty...cant delete a node\n");
+                 }
+                 else if(head->next==head)
+                 {
+                     printf("node deleted=%d\n",head->data);
+                     free(head);
+                     head=NULL;
+                 }
+                 else
+                 {
+                     temp=head;
+                     while(temp->next!=head)
+                     {
+                         prev=temp;
+                         temp=temp->next;
+                     }
+                     printf("node deleted=%d\n",temp->data);
+                     free(temp);
+                     prev->next=head;
+                 }
+                 return(head);
+}
+
+
+void display(NODE *head)
+{
+    if(head==NULL)
+                {
+                    printf("Linked list is empty\n");
+                }
+                else
+                {
+                printf("the linked list is as below\n");
+                   temp=head;
+                   while(temp->next!=head)
+                   {
+                       printf("%d->",temp->data);
+                       temp=temp->next;
+                   }
+            printf("%d->",temp->data);
+
+                   printf("\n");
+                }
+}
diff --git a/src/Chapter_04_Stacks/Linked list program(UDF).c b/src/Chapter_04_Stacks/Linked list program(UDF).c
new file mode 100644
index 0000000..47fabb4
--- /dev/null
+++ b/src/Chapter_04_Stacks/Linked list program(UDF).c	
@@ -0,0 +1,164 @@
+ #include<stdio.h>
+#include<stdlib.h>
+struct CET
+{
+char name[20];
+int marks;
+char city[20];
+int phone;
+struct CET *next;
+};
+typedef struct CET NODE;
+NODE *LLnode,*head,*temp,*prev;
+NODE* insert_at_front(NODE *);
+NODE* insert_at_end(NODE *);
+NODE* delete_at_front(NODE *);
+NODE* delete_at_end(NODE *);
+void display(NODE *);
+
+
+main()
+{
+int ch;
+head=NULL;
+
+do
+{
+    printf("1--insert node at the front\n");
+    printf("2--insert node at the end\n");
+    printf("3--delete a node at the front\n");
+    printf("4--delete a node at the end\n");
+    printf("5--display the linked list\n");
+   printf("6--close the program\n");
+
+printf("enter your choice\n");
+scanf("%d",&ch);
+switch(ch)
+{
+case 1:  head=insert_at_front(head);
+
+                break;
+case 2: head=insert_at_end(head);
+
+                break;
+case 3:head=delete_at_front(head);
+
+                 break;
+case 4: head=delete_at_end(head);
+
+                 break;
+case 5:   display(head);
+                break;
+case 6: exit(0);break;
+default:printf("Invalid choice\n");
+                break;
+}
+}while(ch!=6);
+
+
+}
+NODE* insert_at_front(NODE *head)
+{
+    LLnode=(NODE *)malloc(sizeof(NODE));
+                printf("enter the name, marks, city, phone\n");
+                scanf("%s%d%s%d",&LLnode->name,&LLnode->marks,&LLnode->city,&LLnode->phone);
+
+                if(head==NULL)
+                {
+                    head=LLnode;
+                    head->next=NULL;
+                }
+                else
+                {
+                  LLnode->next=head;
+                  head=LLnode;
+                }
+        return(head);
+
+}
+
+NODE* insert_at_end(NODE *head)
+{
+    LLnode=(NODE *)malloc(sizeof(NODE));
+                printf("enter the name, marks, city, phone\n");
+                scanf("%s%d%s%d",&LLnode->name,&LLnode->marks,&LLnode->city,&LLnode->phone);
+                LLnode->next=NULL;
+                if(head==NULL)
+                {
+                    head=LLnode;
+                }
+                else
+                {
+                    temp=head;
+                    while(temp->next!=NULL)
+                    {
+                        temp=temp->next;
+                    }
+                    temp->next=LLnode;
+                }
+        return(head);
+
+}
+
+NODE* delete_at_front(NODE *head)
+{
+    if(head==NULL)
+                {
+                    printf("Linked list is empty...cant delete a node\n");
+                 }
+                 else
+                 {
+                     temp=head;
+                     printf("node deleted=%s%d%s%d\n",temp->name,temp->marks,temp->city,temp->phone);
+                     head=head->next;
+                     free(temp);
+                 }
+                return(head);
+}
+
+NODE*  delete_at_end(NODE *head)
+{
+    if(head==NULL)
+                {
+                    printf("Linked list is empty...cant delete a node\n");
+                 }
+                 else if(head->next==NULL)
+                 {
+                     printf("node deleted=%s%d%s%d\n",temp->name,temp->marks,temp->city,temp->phone);
+                     free(head);
+                     head=NULL;
+                 }
+                 else
+                 {
+                     temp=head;
+                     while(temp->next!=NULL)
+                     {
+                         prev=temp;
+                         temp=temp->next;
+                     }
+                     printf("node deleted=%s%d%s%d\n",temp->name,temp->marks,temp->city,temp->phone);
+                     free(temp);
+                     prev->next=NULL;
+                 }
+                 return(head);
+}
+
+
+void display(NODE *head)
+{
+    if(head==NULL)
+              {
+                    printf("Students data list is empty\n");
+                }
+                else
+                {
+                printf("Students information is as below\n");
+                   temp=head;
+                   while(temp!=NULL)
+                   {
+                       printf("name= %s\nmarks= %d\ncity= %s\nphone= %d\n",temp->name,temp->marks,temp->city,temp->phone);
+                       temp=temp->next;
+                   }
+                   printf("\n");
+                }
+}
diff --git a/src/Chapter_04_Stacks/StacksLinkedListUDF.c b/src/Chapter_04_Stacks/StacksLinkedListUDF.c
new file mode 100644
index 0000000..0851d32
--- /dev/null
+++ b/src/Chapter_04_Stacks/StacksLinkedListUDF.c
@@ -0,0 +1,110 @@
+#include<stdio.h>
+#include<stdlib.h>
+struct stack
+{
+int data;
+struct stack *next;
+};
+typedef struct stack NODE;
+NODE *top,*temp,*LLnode,*nnode;
+NODE *push(NODE *);
+NODE *pop(NODE*);
+void display(NODE*);
+NODE *get_node();
+main()
+{
+int ch;
+top=NULL;
+do
+{
+   printf("1--push\n");
+   printf("2--pop\n");
+   printf("3--display\n");
+   printf("4--exit\n");
+   printf("enter the choice\n");
+   scanf("%d",&ch);
+   switch(ch)
+   {
+   case 1:  top=push(top);
+                       break;
+    case 2: if(top==NULL)
+                    printf("stack is empty\n");
+                    else
+                    {
+                       top=pop(top);
+                    }
+                    break;
+    case 3: display(top);break;
+    case 4: exit(0);break;
+    default: printf("Invalid choice\n");break;
+   }
+}while(ch!=4);
+}
+
+NODE *get_node()
+{
+   nnode=(NODE*)malloc(sizeof(NODE));
+    if(nnode==NULL)
+    {
+     printf("memory not allocated\n");
+     exit(0);
+    }
+    else
+    {
+      printf("enter the element\n");
+      scanf("%d",&nnode->data);
+    }
+     return(nnode);
+
+}
+
+NODE *push(NODE *top)
+{
+    LLnode=get_node();
+    if(top==NULL)
+    {
+   top=LLnode;
+    LLnode->next=NULL;
+    }
+    else
+    {
+    LLnode->next=top;
+    top=LLnode;
+    }
+    return(top);
+
+
+}
+
+NODE *pop(NODE *top)
+{
+    printf("the element poped=%d\n",top->data);
+    if(top->next==NULL)
+    {
+      free(top);
+      top=NULL;
+    }
+    else
+    {
+       temp=top;
+       top=top->next;
+       free(temp);
+    }
+    return(top);
+}
+
+void display(NODE *top)
+{
+    if(top==NULL)
+    printf("stack is empty\n");
+    else
+    {
+       temp=top;
+       printf("stack elements are\n");
+       while(temp!=NULL)
+       {
+          printf("%d\n",temp->data);
+          temp=temp->next;
+       }
+    }
+}