1#include "stack.h"
 2#include <stdlib.h>
 3
 4Node *node_init(void *data) {
 5  Node *node = malloc(sizeof(Node));
 6  node->next = NULL;
 7  node->data = data;
 8  return node;
 9}
10
11Stack *stack_init() {
12  Stack *stack = malloc(sizeof(Stack));
13  stack->head = NULL;
14  return stack;
15}
16
17int stack_size(Stack *self) {
18  if (!self || !self->head)
19    return 0;
20
21  int count = 0;
22  Node *current = self->head;
23  while (current) {
24    ++count;
25    current = current->next;
26  }
27
28  return count;
29}
30
31void *stack_peek(Stack *self) {
32  if (self->head)
33    return self->head->data;
34  return NULL;
35}
36
37void stack_push(Stack *stack, void *data) {
38  Node *node = node_init(data);
39  node->next = stack->head;
40  stack->head = node;
41}
42
43void *stack_pop(Stack *self) {
44  if (self->head) {
45    Node *tmp = self->head;
46    void *data = tmp->data;
47    self->head = self->head->next;
48    free(tmp);
49    return data;
50  }
51  return NULL;
52}