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

// procedure list
struct list * init();
void print(struct list * head);
int length(struct list * head);
int search(struct list * head, int key);

// list data type
struct list
{
  int value;
  struct list *next;
};


// init a list interacting with the user
struct list * init()
{
  // a pointer to the head, to be returned
  struct list * head;

  // a pointer always pointing to the end of the list
  struct list * list_pointer = NULL;

  // auxiliary variabiles
  int input = -1;

  // ask for input, untill it is "0"
  while( input  != 0 )
    {
      // ask input
      printf("Inserisci un numero (0 per terminare) : ");
      scanf("%d", &input);

      // if it is not 0, add it to the list, otherwise exit from while
      if(input != 0)
	{
	  // special care for empty list when list_pointer is NULL
	  if(list_pointer == NULL)
	    {
	      // create the head object
	      head  = (struct list *) malloc( sizeof(struct list *) );
	
	      // and point to the head
	      list_pointer = head;
	    }
	  else // the general case, when the list is not empty, and list_pointer points to the last inserted element
	    {
	      // allocate memory for a new record
	      list_pointer->next = (struct list *) malloc( sizeof(struct list *) );
	      
	      // shift the pointer
	      list_pointer = list_pointer->next;
	    }
	  
	  // store input value
	  list_pointer->value = input;
	}
    }

  // set the end of the list
  list_pointer->next = NULL; 

  // return the pointer to the head
  return head;
}


// print a list
void print(struct list * head)
{
  // declare a pointer pointing to the head
  struct list * list_pointer = head;
  
  // loop over whole list
  printf("[");
  while (list_pointer != 0)
    {
      // print the pointed value
      printf ("\t%d", list_pointer->value);

      // shift the pointer
      list_pointer = list_pointer->next;
    }
  printf("\t]\n");
}


// search for an element in a list, if it is found, return its index in the list, otherwise return -1
int search(struct list * head, int key)
{
  // declare a pointer pointing to the head
  struct list * list_pointer = head;
  int i = 0;

  // loop over whole list
  while (list_pointer != 0)
    {
      // if it is found
      if(list_pointer->value == key)
	return i; // then return its index
      else // otherwise shift the pointer
	{
	  i++;
	  list_pointer = list_pointer->next;
	}
    }

  return -1;
}

// compute the length of a list
int length(struct list * head)
{
  // declare a pointer pointing to the head
  struct list * list_pointer = head;
  int count = 0;
    
  // loop over whole list
  while (list_pointer != 0)
    {
   count++; // update counter
      // and shift the pointer
            list_pointer = list_pointer->next;
    }
  
  return count;
}

/*****************************************/
void main ()
{
  
  struct list *list_pointer;
  int i, j;

  printf("Questo e' un programma semplice che dovete essere in grado di capire alla fine di questo semplice corso sulla programmazione in C. \n\nAdesso tu, caro utente, interagirai con me per creare una lista di interi...\n");

  list_pointer = init();

  printf("\nBenissimo, ti stampo un riepilogo della lista che hai inserito: ");

  print(list_pointer);

  printf("Hai inserito %d elementi.\n", length(list_pointer));

  printf("Adesso inserisci un valore intero qualunque, ed io lo cerchero nella lista: ");
  scanf("%d",&i);

  j = search(list_pointer,i);
  
  if(j == -1)
    printf("\nElemento NON trovato nella lista!!");
  else
    {
      printf("\nElemento trovato in posizione %d nella lista!!",j);
    }
  
}