diff --git a/2.c b/2.c
index 67c49c2..1f35bb2 100644
--- a/2.c
+++ b/2.c
@@ -82,9 +82,10 @@ int main() {
   delete (&head, 2);
   reverse(&head);
 
-  while (head != NULL) {
-    printf("%d ", head->sid);
-    head = head->next;
+  student *cur = head;
+  while (cur != NULL) {
+    printf("%d ", cur->sid);
+    cur = cur->next;
   }
 
   // free
diff --git a/3.c b/3.c
new file mode 100644
index 0000000..e12f5aa
--- /dev/null
+++ b/3.c
@@ -0,0 +1,76 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct Employee employee;
+struct Employee {
+  int eid;
+  struct Employee *next;
+  struct Employee *prev;
+};
+
+typedef struct Employees employees;
+struct Employees {
+  uint len;
+  struct Employee *head;
+  struct Employee *tail;
+};
+
+employees *init() {
+  employees *list = malloc(sizeof(employees));
+  list->len = 0;
+  list->head = NULL;
+  list->tail = NULL;
+
+  return list;
+}
+
+void insert(employees *list, uint eid) {
+  employee *new = malloc(sizeof(employee));
+  new->eid = eid;
+  new->prev = NULL;
+  new->next = list->head;
+
+  if (list->head)
+    list->head->prev = new;
+  else
+    list->tail = new;
+
+  list->head = new;
+  list->len++;
+}
+
+void delete (employees *list) {
+  employee *prev = list->tail->prev;
+
+  free(list->tail);
+
+  if (prev) {
+    prev->next = NULL;
+    if (prev->prev == NULL)
+      list->head = prev;
+  }
+
+  list->tail = prev;
+  list->len--;
+}
+
+int main() {
+  employees *list = init();
+  insert(list, 4);
+  insert(list, 20);
+  insert(list, 300);
+  insert(list, 44);
+  delete (list);
+
+  employee *cur = list->head;
+  while (cur != NULL) {
+    printf("%d ", cur->eid);
+    cur = cur->next;
+  }
+
+  // free
+  while (list->tail != NULL)
+    delete (list);
+
+  free(list);
+}
diff --git a/3.png b/3.png
new file mode 100644
index 0000000..29e18cd
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diff --git a/5.c b/5.c
new file mode 100644
index 0000000..5b08256
--- /dev/null
+++ b/5.c
@@ -0,0 +1,72 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct Stacks stacks;
+struct Stacks {
+  int *stack;
+  uint s1, s2;
+  uint l1, l2;
+};
+
+stacks *init(uint s1, uint s2) {
+  stacks *s = malloc(sizeof(stacks));
+  s->stack = malloc(sizeof(int) * (s1 + s2));
+  s->s1 = s1, s->s2 = s2;
+  s->l1 = s->l2 = 0;
+
+  return s;
+}
+
+void push(uint stack, stacks *s, int elem) {
+  if (stack != 1 && stack != 2)
+    fprintf(stderr, "Invalid stack number\n");
+
+  if (stack == 1) {
+    if (s->l1 == s->s1) {
+      fprintf(stderr, "Stack 1 Overflow");
+      return;
+    }
+    s->stack[s->l1++] = elem;
+    return;
+  }
+
+  if (s->l2 == s->s2) {
+    fprintf(stderr, "Stack 2 Overflow");
+    return;
+  }
+  s->stack[s->s1 + s->l2++] = elem;
+}
+
+int pop(uint stack, stacks *s) {
+  if (stack != 1 && stack != 2)
+    fprintf(stderr, "Invalid stack number\n");
+
+  if (stack == 1) {
+    if (!s->l1) {
+      fprintf(stderr, "Stack 1 Underflow");
+      exit(1);
+    }
+    return s->stack[--s->l1];
+  }
+
+  if (!s->l2) {
+    fprintf(stderr, "Stack 2 Underflow");
+    exit(1);
+  }
+  return s->stack[s->s1 + --s->l2];
+}
+
+int main() {
+  int s1 = 8, s2 = 4; // sizes
+  stacks *s = init(s1, s2);
+  push(1, s, 3);
+  push(1, s, 99);
+  push(2, s, 6);
+  push(1, s, 4);
+
+  printf("%d ", pop(1, s));
+  printf("%d", pop(2, s));
+
+  free(s->stack);
+  free(s);
+}
diff --git a/5.png b/5.png
new file mode 100644
index 0000000..c77221e
Binary files /dev/null and b/5.png differ
diff --git a/6.c b/6.c
new file mode 100644
index 0000000..2b77b1e
--- /dev/null
+++ b/6.c
@@ -0,0 +1,48 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct Node node;
+struct Node {
+  int id;
+  struct Node *next;
+};
+
+int peek(node *stack) { return stack->id; }
+
+void push(node **stack, int id) {
+  node *new = malloc(sizeof(node));
+  new->id = id;
+
+  new->next = *stack;
+  *stack = new;
+}
+
+int pop(node **stack) {
+  int id = (*stack)->id;
+  node *next = (*stack)->next;
+  free(*stack);
+  *stack = next;
+  return id;
+}
+
+void traverse(node *stack) {
+  while (stack != NULL) {
+    printf("%d ", stack->id);
+    stack = stack->next;
+  }
+  printf("\n");
+}
+
+int main() {
+  node *stack = NULL;
+  push(&stack, 4);
+  push(&stack, 99);
+  push(&stack, 23);
+  printf("Pop: %d\n", pop(&stack));
+  printf("Traverseal: ");
+  traverse(stack);
+
+  // free
+  while (stack != NULL)
+    pop(&stack);
+}
diff --git a/6.png b/6.png
new file mode 100644
index 0000000..7388627
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diff --git a/7.c b/7.c
new file mode 100644
index 0000000..471c022
--- /dev/null
+++ b/7.c
@@ -0,0 +1,66 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct Node node;
+struct Node {
+  int id;
+  struct Node *next;
+};
+
+typedef struct Queue queue;
+struct Queue {
+  node *head;
+  node *tail;
+};
+
+int peek(queue *q) { return q->head->id; }
+
+void insert(queue *q, int id) {
+  node *new = malloc(sizeof(node));
+  new->id = id;
+  new->next = NULL;
+
+  if (q->tail)
+    q->tail->next = new;
+  else
+    q->head = new;
+
+  q->tail = new;
+}
+
+void delete (queue *q) {
+  if (!q->head)
+    return;
+
+  node *next = q->head->next;
+
+  free(q->head);
+
+  q->head = next;
+
+  if (!q->head)
+    q->tail = NULL;
+}
+
+void display(queue *q) {
+  node *cur = q->head;
+  while (cur != NULL) {
+    printf("%d ", cur->id);
+    cur = cur->next;
+  }
+  printf("\n");
+}
+
+int main() {
+  queue *q = malloc(sizeof(queue));
+  insert(q, 56);
+  insert(q, 3);
+  insert(q, 99);
+  delete(q);
+  display(q);
+
+  // free
+  while (q->head != NULL)
+    delete(q);
+  free(q);
+}
diff --git a/7.png b/7.png
new file mode 100644
index 0000000..730f0cd
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