Call by function structures

[adv100]

I am trying to create a linked list dequeed. I have created my add a word which adds a word. Because i change the head and the tail of list i was trying to use call by reference so i could change both the head and the tail of the list. I am not sure what i am doing wrong because it isn't changing the address outside of the function. Head and tail are NULL when they are sent. Head and Tail get addresses while in the functions and then after leaving the function HEAD and TAIL become NULL again. I dont understand why this is happening? Thanks for any help. I could add all my code but i was hoping someone would be able to help with just this? Thanks

Call to the function

    #include <iostream>
#include <cstdlib>
#include <fstream>
#include <stdio.h>
#include <cstring>
#include <strings.h>
#include <cctype>

struct node
{
char word [10];
node *next;
node *prev;
};


using namespace std;


int display ();
void switcheroo (int, struct node*, struct node*);
void  add_Word (char [], struct node**, struct node**);
void delete_Word (char [], struct node **, struct node **);
void display_Queue (struct node*);
void display_Stack (struct node*);
void search_List (char[], struct node*);
struct node* makeNode (void);

int main ( )
{

system ("clear");
int pick;
struct node *head;
struct node *tail;
head = NULL;

cout << endl << head << " first call"<< endl;

while (pick != 6)
{
cout << endl << head << " 888888"  << endl;
pick = display ();
switcheroo (pick, head, tail);
}

return 0;
}

/*******************************************************************/

int display ()
{

int user_choice;

  cout <<"What would you like to do?\n\n";  
  cout <<"Press 1   Add a word\n";
  cout <<"Press 2   Delete a word\n";
  cout <<"Press 3   Display the data in Queue order\n";
  cout <<"Press 4   Display the data in stack order\n"; 
  cout <<"Press 5   Search the list for a word\n";
  cout <<"Press 6   Quit\n";
  cin >> user_choice;

  return user_choice;
}
/********************************************************************/
void switcheroo (int pick, struct node* head, struct node*tail)
{
  char word [10];
  switch (pick)
        {
    case 1:
        cout << "Please enter a word:\n";
        cin  >> word;
        add_Word(word, &head, &tail);
        break;
    case 2:
        display_Queue(head);
        cout << "\n\nEnter a word to delete\n";
        cin >> word;
        delete_Word(word, &head, &tail);
        break;
    case 3:
        display_Queue(head);
        break;
    case 4:
        display_Stack(tail);
        break;
    case 5: 
        display_Queue(head);
        cout << "\n\nWhat word would you like to search for?\n";
        cin >> word;
        search_List(word, tail);
        break;
    case 6:
        return;
        }
}

/*******************************************************************/
void  add_Word ( char word[], struct node **head, struct node **tail)
{
  struct node *var, *temp;
  var = makeNode();
  strcpy (var->word, word);
  
  cout << endl << *head << endl;
   cout << endl << *tail << endl;

  if (*head == NULL)
  {
  *head = var;
  cout << *head << endl;
  (*head)->prev = NULL;
  (*head)->next = NULL;
  tail = head;
  

  cout << endl << "00000" << *head << endl;
  }
  else 
  {
  cout << "--------------" << endl;
  temp = var;
  temp->prev = NULL;
  temp->next = *head;
  (*head)->prev = temp;
  *head = temp;
  }
   
}
/*******************************************************************/


struct node* makeNode (void)
{
  struct node* newptr;

  newptr = new struct node;
  if (newptr)
    newptr->next = NULL;

  return newptr;
}

/*******************************************************************/

void display_Queue(struct node * x)
{
  int n = 01;
  while (x != NULL)
  {
  cout << "---" << x->word << "---" << n << endl;
  n++;
  x = x->prev;
  }

  return;
} 
/*******************************************************************/
void display_Stack (struct node *x)
{
  int n=1;
  while (x != NULL)
  {
  cout << "---" << x->word << "---" << n << endl;
  n++;
  x = x->next;
  }
  
  return;
}
/*******************************************************************/
void delete_Word(char word [], struct node **head, struct node **tail) 
{

  struct node *palabra, *x;
  int n = 0; 
  x = *head; 
  char copy [10];
  while (x != NULL)
  {
  strcpy (copy,x->word); 
   cout << "!!!!!!!!!!" << x->word << endl;  
  if (strcasecmp (x->word, word)==0)
    {
        cout << "**********"<< endl;
    palabra = x;
    n++;
    }
  x = x->next;
  }

  if (n==0)
  cout << "NO word to delete!!! try again";

 
  if (n==1)
{  
  if ((palabra->next == NULL) && (palabra->prev == NULL))
    { 
    delete (palabra);
    *head = NULL;
    *tail = NULL;
    }
  else if (palabra->next == NULL)
    {
    *tail = palabra->prev;
    (*tail)->next = NULL;
    delete (palabra);
    }
  else if(palabra->prev == NULL)      
    {
    *head = palabra->next;
    (*head)->prev = NULL;
    delete (palabra);
    }
  else if((palabra->next != NULL)&&(palabra->prev!= NULL))
    {
    palabra->next->prev = palabra->prev;
    palabra->prev->next = palabra->next;
    delete (palabra);
    }
}
}
/*******************************************************************/
void search_List (char word[], struct node *x)
{
  int n =1;
  cout << endl << word << endl;
   

  while (x != NULL)
  {
    if (strcasecmp (x->word, word)==0)
        {
        cout << "Your word has been found\n";
        cout << word << " is number:  " << n << " in the list\n\n";
        }
    n++;
    x = x->prev;
  }
}

[ak16]

What is this?????????

[adv100]

What does that mean? what is this?
it is a doubly linked list written in c++ that doesn't work because i switched from global variables to local varibles and am trying to pass by reference but my pass by references are not changing anyhting out side of the function.
I need to understand what i am doing wrong. specifically i want to understand why my pass by references of HEAD and TAIL in the add_Word function and delete_Word function are not passing by reference. Why are they not changing the variables outside of the function.