diff --git a/Binary Search Tree/README.md b/Binary Search Tree/README.md
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+++ b/Binary Search Tree/README.md	
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+# Binary Search Tree (BST)
+
+This directory contains the implementation of a Binary Search Tree (BST) in C. The BST allows efficient storage and retrieval of data in a sorted manner.
+
+## Files
+
+- `bst-definition.c`: This file contains the implementation of various functions related to the BST, including `getnode()`, `insert()`, `inorder()`, `preorder()`, `postorder()`, `delete()`, and `minvaluenode()`.
+- `bst-main.c`: This file provides a user interface to interact with the BST. It allows users to insert elements into the tree, delete elements from the tree, and perform tree traversals.
+- `bst.h`: This header file contains the structure definition for the `bstree` node and function prototypes for the BST operations.
+
+## Compilation
+
+To compile the program, you can use the following commands:
+
+```bash
+gcc -c bst-definition.c -o bst-definition.o
+gcc -c bst-main.c -o bst-main.o
+gcc bst-definition.o bst-main.o -o program
+```
+
+## Usage
+
+After compiling the program, you can run it using the following command:
+
+```bash
+./program
+```
+Once the program starts, you will be presented with a menu to perform different operations on the BST:
+
+1. Insert Element in Tree: This option allows you to insert a new element into the BST.
+2. Delete Element from Tree: This option allows you to delete an element from the BST.
+3. Tree Traversals: This option displays the pre-order, in-order, and post-order traversals of the BST.
+4. EXIT: This option exits the program.
+
+## Note
+
+Ensure that all the necessary files (bst-definition.c, bst-main.c, bst.h) are present in the same directory before compiling and running the program.
+
+Feel free to explore and modify the code to suit your requirements. Enjoy working with Binary Search Trees!
diff --git a/Stack ADT/using opaque pointer/README.md b/Stack ADT/using opaque pointer/README.md
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+++ b/Stack ADT/using opaque pointer/README.md	
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+# Implementation of stack using opaque pointer in C
+
+This showcases an implementation of a stack using the `opaque pointer` concept in the `C` programming language. It consists of three files:
+
+- `stack.h`: This is the header file that contains the declarations of the functions and data structures used in the stack implementation.
+- `stack.c`: This file contains the actual implementation of the stack functions defined in the header file.
+- `main.c`: This is the driver code that demonstrates how to use the stack functions.
+
+### > How to compile & run
+
+- Compile with `gcc stack.c main.c`.
+- Run with `./a.out` (Linux environment) or `.\a.exe` (Windows environment).
diff --git a/Stack ADT/using opaque pointer/array based implementation/main.c b/Stack ADT/using opaque pointer/array based implementation/main.c
new file mode 100644
index 0000000..0a95c01
--- /dev/null
+++ b/Stack ADT/using opaque pointer/array based implementation/main.c	
@@ -0,0 +1,15 @@
+#include "stack.h"
+#define create(stack) Stack*stack=create()
+
+int main()
+{
+    create(stack);
+    
+    for (int i = 1; i <= 10; push(stack, i++));
+    pop(stack);
+    pop(stack);
+    pop(stack);
+    top(stack);
+    
+    return 0;
+}
\ No newline at end of file
diff --git a/Stack ADT/using opaque pointer/array based implementation/stack.c b/Stack ADT/using opaque pointer/array based implementation/stack.c
new file mode 100644
index 0000000..d33aadb
--- /dev/null
+++ b/Stack ADT/using opaque pointer/array based implementation/stack.c	
@@ -0,0 +1,54 @@
+#include "stack.h"
+#include <stdlib.h>
+#define length(arr) (sizeof (arr) / sizeof *(arr))
+
+struct Stack
+{
+    int arr[10];
+    int top;
+};
+
+Stack *create(void)
+{
+    Stack *stack = malloc(sizeof(Stack));
+    if (!stack)
+        return NULL;
+    stack->top = -1;
+    return stack;
+}
+
+inline static _Bool overflow(Stack *stack)
+{
+    return length(stack->arr) - 1 == stack->top;
+}
+
+inline static _Bool underflow(Stack *stack)
+{
+    return -1 == stack->top;
+}
+
+int printf(const char *, ...);
+
+void push(Stack *stack, int data)
+{
+    if (overflow(stack))
+        printf("Stack overflow!\n");
+    else
+        stack->arr[++(stack->top)] = data;
+}
+
+void pop(Stack *stack)
+{
+    if (underflow(stack))
+        printf("Stack underflow!\n");
+    else
+        printf("%d\n", stack->arr[(stack->top)--]);
+}
+
+void top(Stack *stack)
+{
+    if (underflow(stack))
+        printf("Stack underflow!\n");
+    else
+        printf("%d\n", stack->arr[stack->top]);
+}
\ No newline at end of file
diff --git a/Stack ADT/using opaque pointer/array based implementation/stack.h b/Stack ADT/using opaque pointer/array based implementation/stack.h
new file mode 100644
index 0000000..b11999c
--- /dev/null
+++ b/Stack ADT/using opaque pointer/array based implementation/stack.h	
@@ -0,0 +1,10 @@
+#ifndef STACK_H
+#define STACK_H
+
+typedef struct Stack Stack;
+Stack *create(void);
+void push(Stack *, int);
+void pop(Stack *);
+void top(Stack *);
+
+#endif
\ No newline at end of file
diff --git a/Stack ADT/using opaque pointer/linked list based implementation/main.c b/Stack ADT/using opaque pointer/linked list based implementation/main.c
new file mode 100644
index 0000000..d2957b7
--- /dev/null
+++ b/Stack ADT/using opaque pointer/linked list based implementation/main.c	
@@ -0,0 +1,16 @@
+#include "stack.h"
+#define create(stack) Stack*stack=create()
+
+int main()
+{
+    create(stack);
+    
+    for (int i = 1; i <= 10; push(stack, i++));
+    pop(stack);
+    pop(stack);
+    pop(stack);
+    top(stack);
+    
+    
+    return 0;
+}
\ No newline at end of file
diff --git a/Stack ADT/using opaque pointer/linked list based implementation/stack.c b/Stack ADT/using opaque pointer/linked list based implementation/stack.c
new file mode 100644
index 0000000..6bca677
--- /dev/null
+++ b/Stack ADT/using opaque pointer/linked list based implementation/stack.c	
@@ -0,0 +1,78 @@
+#include "stack.h"
+#include <stdlib.h>
+#define capacity 10
+
+struct Node
+{
+    int data;
+    Node *next;
+};
+
+struct Stack
+{
+    Node *top;
+    int count;
+};
+
+Stack *create(void)
+{
+    Stack *stack = malloc(sizeof(Stack));
+    if (!stack)
+        return NULL;
+    stack->top = NULL;
+    stack->count = 0;
+    return stack;
+}
+
+inline static _Bool overflow(Stack *stack)
+{
+    return capacity == stack->count;
+}
+
+inline static _Bool underflow(Stack *stack)
+{
+    return !stack->count;
+}
+
+int printf(const char *, ...);
+
+void push(Stack *stack, int data)
+{
+    if (overflow(stack))
+        printf("Stack overflow!\n");
+    else
+    {
+        Node *newNode = malloc(sizeof(Node));
+        if (!newNode)
+            return;
+        if (!stack->count) // for the first inserted node
+            newNode->next = NULL;
+        newNode->data = data;
+        newNode->next = stack->top;
+        stack->top = newNode;
+        stack->count++;
+    }
+}
+
+void pop(Stack *stack)
+{
+    if (underflow(stack))
+        printf("Stack underflow!\n");
+    else
+    {
+        printf("%d\n", stack->top->data);
+
+        Node *del = stack->top;
+        stack->top = stack->top->next;
+        free(del);
+        stack->count--;
+    }
+}
+
+void top(Stack *stack)
+{
+    if (underflow(stack))
+        printf("Stack underflow!\n");
+    else
+        printf("%d\n", stack->top->data);
+}
\ No newline at end of file
diff --git a/Stack ADT/using opaque pointer/linked list based implementation/stack.h b/Stack ADT/using opaque pointer/linked list based implementation/stack.h
new file mode 100644
index 0000000..6ab45f9
--- /dev/null
+++ b/Stack ADT/using opaque pointer/linked list based implementation/stack.h	
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+#ifndef STACK_H
+#define STACK_H
+
+typedef struct Node Node;
+typedef struct Stack Stack;
+Stack *create(void);
+void push(Stack *, int);
+void pop(Stack *);
+void top(Stack *);
+
+#endif
\ No newline at end of file