linked_list.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

struct list_item {
  struct list_item *next;
  int data;
};

typedef struct list_item ListItem;

ListItem *head;
ListItem *tail;

ListItem *allocate_list_item() {
  return (ListItem*) malloc(sizeof(ListItem));
}

void init_linked_list() {
  head = allocate_list_item();
  tail = allocate_list_item();
}

void push(int data) {
  ListItem *new_item = allocate_list_item();
  new_item->data = data;

  if(tail->next == NULL) {
    tail->next = new_item;
    head->next = new_item;
  }
  else {
    ListItem *current_tail = tail->next;
    tail->next = new_item;
    current_tail->next = new_item;
  }
}

int first() {
  if(head->next == NULL) {
    printf("No items yet missy.\n");
    return -1;
  }
  else {
    ListItem *to_be_next = head->next->next;
    int data = head->next->data;
    free(head->next);

    if(to_be_next != NULL) {
      head->next = to_be_next;
    }
    else {
      head->next = NULL;
      tail->next = NULL;
    }
    return data;
  }
}

int main() {
  init_linked_list();
  push(33);
  printf("Firsty: %d\n", first());
  return 0;
}