diff --git a/theory/data_structure/binary_trees.cpp b/theory/data_structure/binary_trees.cpp
new file mode 100644
index 0000000..4ef7480
--- /dev/null
+++ b/theory/data_structure/binary_trees.cpp
@@ -0,0 +1,94 @@
+#include <iostream>
+#include <vector>
+#include <string>
+#include <algorithm>
+
+// Implementation of binary search tree
+class Node {
+
+    public:
+        int value;
+        int height;
+        Node *left;
+        Node *right;
+
+        // constructor 
+        Node(int value) {
+            this->value = value;
+            this->left = nullptr;
+            this->right = nullptr;
+            this->height = 0;
+        }
+};
+
+// Creating new nodes, the first'll be the root
+Node *newNode(int n) {
+    return new Node(n);
+}
+
+// insert nodes
+void insert(Node *&root, int n) {
+
+    // if the root is empty we create a new tree, n being root
+    if(root == nullptr) {
+        newNode(n);
+        return;
+    }
+
+    // else, check if n is greater than or lesser than actual node
+    Node *tmp = root;
+
+    // check the left case
+    if(n < tmp->value) {
+        if(tmp->left == nullptr) {
+            tmp->left = newNode(n);
+            return;
+        } else
+            insert(tmp->left,n);
+    } else if(n > tmp->value) // check the right case
+        if(tmp->right == nullptr) {
+            tmp->right = newNode(n);
+            return;
+        } else
+            insert(tmp->right,n);
+
+}
+
+// printing tree values in pre-order method
+void print(Node *root) {
+
+    // base case
+    if(root == nullptr)
+        return;
+    
+    // recursion calls
+    std::cout << root->value << " ";
+    print(root->left);
+    print(root->right);
+
+}
+
+// Balancing Binary tree
+
+
+
+
+
+
+
+int main(void){
+
+    Node *tree = newNode(12);
+    insert(tree,9);
+    insert(tree,7);
+    insert(tree,10);
+    insert(tree,13);
+    insert(tree,14);
+
+    print(tree);
+
+
+}
+
+
+
diff --git a/theory/data_structure/extract_digit.cpp b/theory/data_structure/extract_digit.cpp
new file mode 100644
index 0000000..9960bc8
--- /dev/null
+++ b/theory/data_structure/extract_digit.cpp
@@ -0,0 +1,18 @@
+#include <iostream>
+
+// i is the digit that want
+// the order is right to left
+int extract_digit(int n, int i) {
+
+    if (i == 1)
+        return n%10;
+
+    return extract_digit(n/10,i-1);
+
+}
+
+int main(void){
+
+    std::cout << extract_digit(1223456789,2);
+
+}
\ No newline at end of file
diff --git a/theory/data_structure/linked_list.cpp b/theory/data_structure/linked_list.cpp
new file mode 100644
index 0000000..373b3b0
--- /dev/null
+++ b/theory/data_structure/linked_list.cpp
@@ -0,0 +1,160 @@
+#include <iostream>
+#include <vector>
+#include <list>
+
+// Singled linked list
+class Node {
+    public:
+        int data;
+        int size = 0;
+        Node *next;
+
+    // methods
+    void head(Node *head) {
+        if(head != nullptr)
+            std::cout << head->data << std::endl;
+        else
+            std::cout << "NULL" << std::endl;
+    }
+
+    void tail(Node *head) {
+
+        if(head == nullptr) {
+            std::cout << "NULL" << std::endl;
+            return;
+        }
+        
+        Node *tmp = head;
+        while(tmp->next != nullptr)
+            tmp = tmp->next;
+
+        std::cout << tmp->data << std::endl;
+
+    }
+
+    int getSize(Node *head) {
+        Node *tmp = head;
+        while(tmp->next != nullptr) {
+            head->size++;
+            tmp = tmp->next;
+        }
+        return head->size;
+    }
+
+
+    // constructor
+        Node(int data) {
+            this->data = data;
+            next = nullptr;
+        }
+};
+
+// Creating a new node
+// initialy, adding to the first position, but this function
+// is called to add at the final
+void addFinal(Node *&head, int n) {
+
+    Node *newNode = new Node(n);
+    Node *tmp = head;
+    while(tmp->next != nullptr)
+        tmp = tmp->next;
+
+    tmp->next = newNode;
+
+}
+
+// Adding elements at the first position
+void addFirst(Node *&head, int n) {
+
+    if(head == nullptr) {
+        addFinal(head,n);
+        return;
+    }
+
+    Node *newNode = new Node(n);
+    Node *tmp = head;
+    head = newNode;
+    head->next = tmp;
+
+}
+
+// Adding element at an i position 
+void addAt(Node *&head, int n, int i) {
+
+    if(head == NULL)
+        return;
+    
+    Node *tmp = head;
+    int index = 0;
+    while(index < i-1) {
+        tmp = tmp->next;
+        index++;
+    }
+
+    Node *tmp2 = tmp->next;
+    Node *newNode = new Node(n);
+    tmp->next = newNode;
+    newNode->next = tmp2;
+
+}
+
+// Function to print list
+void printList(Node *head) {
+
+    Node *tmp = head;
+    while(tmp != nullptr) {
+        std::cout << tmp->data << "->";
+        tmp = tmp->next;
+    }
+    std::cout << "NULL" << std::endl;
+
+}
+
+
+int main(){
+
+    // Statically lists
+    Node n1(1);
+    Node n2(2);
+    n1.next = &n2;
+
+    // Dinamically lists
+    Node *n3 = new Node(3);
+    Node *n4 = new Node(4);
+    n3->next = n4;
+
+    //Creating a linked list with n nodes
+    Node *node = new Node(10);
+    addFinal(node,12);
+    addFinal(node,122);
+    addFinal(node,1112);
+    addFinal(node,3412);
+    addFinal(node,2);
+
+    printList(node);
+
+    std::cout << "Atual head: ";
+    node->head(node);
+
+    std::cout << "Atual tail: ";
+    node->tail(node);
+
+    addFirst(node,20);
+    addAt(node,1,2);
+
+    printList(node);
+    std::cout << node->getSize(node) << std::endl;
+
+}
+
+
+
+
+
+
+
+
+
+
+
+