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

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

struct node* head = NULL;
struct node* current = head;

// insert link at the first location
//
void insert(int data) {

  // create a link
  //
  struct node *link = (struct node*) malloc(sizeof(struct node));
  if (link == (struct node*)NULL) {
    fprintf(stdout, "**> Error: memory allocation failed\n");
    exit(-1);
  }
  //  struct node *link = new struct node;

  // link->key = key;
  //
  link->data = data;

  // point it to old first node
  //
  link->next = head;

  // point first to new first node
  //
  head = link;
}

// display the list
//
void printList() {

  struct node *ptr = head;
  printf("\n[head] =>");

  // start from the beginning
  //
  while(ptr != NULL) {
    printf(" %d =>", ptr->data);
    ptr = ptr->next;
  }

  printf(" [null]\n");
}

int main() {

  fprintf(stdout, "initial:\n");
  printList();
  insert(10);
  fprintf(stdout, "after first insertion:\n");
  printList();

  insert(20);
  fprintf(stdout, "after second insertion:\n");
  printList();

  insert(30);
  insert(1);
  insert(40);
  insert(56);
  printList();


  return 0;
}