How to implement user input in a linked list?

Question

For this code I need to be able to use user input of books they have read and put them in a linked list. I have most of the code done but when I try putting books in the list the code isn't adding the books to the list. How can I fix this? this is the function.cpp file

void displayMenu()
{
  cout << "[1]  Add Book\n"
       << "[2]  Size Of List\n"
       << "[3]  Display List\n"
       << "[4]  Remove Last Book\n"
       << "[5]  Delete List\n"
       << "[6]  Quit Program\n"
       << "Enter Choice:  ";
}
int getChoice(int & choice1)
{
  cin >> choice1;   
    while (choice1 < 1 || choice1 > 6) {
      cout << endl;
      cout << "Invalid Entry!!" << endl;
      cout << "Enter Choice:  ";
      cin >> choice1; 
    }
  return choice1;
}
int endProgram(bool & start2)
{
  start2 = false;
  cout << "\n\n\t\tThank you for using this system!!\n\n";
  return start2;
}

void clear()
{
  system("clear");
}

void linkedList::addBook()
{
  Book *ptr;
  bool quit = false;
  string temp = "";
  while (!quit)
    {
      cout << "Enter a book(enter quit to stop): ";
      cin >> temp;

      if (temp == "quit")
      {
        quit = true;
        return;
      }
      ptr = new Book;
      ptr->data = temp;
      ptr->next = NULL;
      if(head == NULL)
      {
        head = ptr;
        tail = ptr;
      }
      else
      {
        tail->next = ptr;
        tail = tail->next;
      }
    }
  return;
}

void linkedList::displayList()
{
  Book *ptr;
  ptr = head;
  while (ptr != NULL)
  {
    cout << ptr->data << endl;
    ptr = ptr->next;
  }
}

void linkedList::listSize()
{
  Book *ptr;
  int counter = 0;
  ptr = head;
  while (ptr != NULL)
  {
    ptr = ptr->next;
    counter++;
  }
  cout << "Number of books in the list: " << counter;
}

void linkedList::deleteLast()
{
  if (head == NULL)
    return;
  if (head->next == NULL) 
  {
    delete head;
    head = NULL;
    return;
  }
  // Find the second last node
  Book* ptr = head;
  while (ptr->next->next != NULL)
    ptr = ptr->next;
  // Delete last node
  delete (ptr->next);
  // Change next of second last
  ptr->next = NULL;
  if(ptr == NULL)
    cout << "Last book is cleared!" << endl;
}

void linkedList::deleteList()
{
  Book *ptr;
  while (head != NULL)
  {
    ptr = head->next;
    delete head;
    head = ptr;
  }
 
  if(head == NULL)
  cout <<"List is cleared!" << endl; 
}

This is the main.cpp file

int main() {
  int choice = 0;
  bool start = true;
  linkedList a;
  while(start != false)
  {
    while(choice != 6)
    {
      displayMenu();
      getChoice(choice);
      if(choice == 1)
      {
        clear();
        a.addBook();
      }
      if(choice == 2)
      {
        clear();
        a.listSize();
      }
      if(choice == 3)
      {
        clear();
        a.displayList();
        cout << endl;
      } 
      if(choice == 4)
      {
        clear();
        a.deleteLast();
      }
      if(choice == 5)
      {
        clear();
        a.deleteList();
      }
      if(choice == 6)
      {
        clear();
        endProgram(start);
      }
    }
  }
}

Last is the function.h file

#include <iostream>
#include <string>
using namespace std;

struct Book
{
  string data;
  Book *next;
};

class linkedList
{
private:
    Book *head,*tail;
public:
  linkedList()
  {
      head = NULL;
      tail = NULL;
  }
  void addBook();
  void displayList();
  void listSize();
  void deleteList();
  void deleteLast();
};

void displayMenu();
int getChoice(int & choice1);
int endProgram(bool & start2);
void clear();

Answer 1

OK got it

In deleteLast

if (head->next == NULL)
{
    delete head;
    return;
}

You forgot to update head

if (head->next == NULL)
{
    delete head;
    head = NULL; <<<<=====
    return;
}

also in the delete function you don't update tail, you need

Book* ptr = head;
while (ptr->next->next != NULL)
    ptr = ptr->next;
// Delete last node
delete (ptr->next);
tail = ptr;<<<<<<<<<<<===================
// Change next of second last
ptr->next = NULL;

You really need to learn to use your debugger