我收到一个错误，说"Not decaled in scope"

这是一个链表程序的作业，我相信我几乎完成了这个程序。在主方法的这几行中，我一直得到4个错误。我想知道是否有人能告诉我瞄准镜出了什么问题。谢谢

错误:' addFirst '未在此范围内声明addFirst(书目);

错误:' addLast '未在此范围内声明addLast(书目);

错误:' isInTheList '未在此范围内声明isInTheList(书目);

错误:' deleteBook '未在此范围内声明deleteBook(书目);

#include <iostream>
    #include <string>
    #include "Program3.h"
    #include <limits>       // for numeric limits
    using namespace std;
//Implementation for class BookList START
void BookList::addFirst(BookNode * book){ //To add a new head node
        book -> setNext(head);
        head = book;
    }
void BookList::addLast(BookNode * book){ //To add a new node at the end
        if(!head){
            addFirst(book);
        }
        else{
            BookNode * temp = head;
            while(temp->getNext() != NULL){
                    temp = temp->getNext();
                }
            temp -> setNext(book);
        }
    }   
void BookList::traverse(){  //TO go through the whole linked list
        BookNode * temp = head;
        while(temp != NULL){
            std::cout << temp -> getTitle()<<std::endl;
            temp = temp -> getNext();
        }
    }

bool BookList::isInTheList(std::string title){  //To check the linked list for a specific title
        BookNode * temp = head;
        while(temp != NULL){
            if(temp -> getTitle() == title){
                return true;
            }
            temp = temp -> getNext();
        }
        return false;
    }

bool BookList::deleteBook(std::string title){   //to delete a book/title

        if(head == NULL){ // or if(!head)  To check if the linked list is empty
            return false;
        }
        BookNode * prev = NULL;
        BookNode * cur = head;

        if( cur -> getTitle() == title){    //Checking if the title is the first node
            head = head -> getNext();
            delete cur;
            return true;
        }
        while(cur != NULL && cur -> getTitle() != title){   //Checking through the linked list for the title
            prev = cur;                                     //The while loop will stop when it has gone though the whole linked list or if it matches with the title
            cur = cur -> getNext();
        }
        if(cur == NULL){        //There is no matching entry
            return false;
        }
        else{
            prev -> setNext( cur -> getNext() );
            delete cur;
            return true;
        }
    }
BookList::~BookList(){

        while( head != NULL){
            string tempTitle = head->getTitle();
            deleteBook(tempTitle);
            cout << "Book " << tempTitle << "has been deleted" <<endl;

        }


    }   

int getUserChoice(){
    int choice = 0;
    cout << "Welcome to the e-library, please make a choice from the menu below" << endl;
    cout << "1. Add a book at the beginning" << endl;
    cout << "2. Add a book at the end" << endl;
    cout << "3. Find a book in the list" << endl;
    cout << "4. Delete a book in the list" << endl;
    cout << "5. Print all the books in the list" << endl;
    cout << "6. Exit " << endl;
    if(cin >> choice){  //confirming that cin succeeded
        if(choice > 0 && choice < 7){
            cin.ignore(); //dump newline character
            return choice;
        }
        else{
            cin.ignore();//dump newline character
            return 0;
        }
    }
    else{
        cin.clear(); //bring cin back from failed status
        cin.ignore(std::numeric_limits<std::streamsize>::max(), 'n');
        return 0;
    }
}




int main(){

    BookList booklist;  //Create an object of ArrayList
    int choice = getUserChoice();   //Prompting user for an input
    while (choice != 6 ){   
        switch(choice){
            case 0: 
                cout << "Invalid choice. Please Choose between 1 and 6." <<endl; // 0 is not a given choice, loop reruns
                break;
            case 1: 
                addFirst(booklist);     
                break;
            case 2:
                addLast(booklist);
                break;
            case 3:
                isInTheList(booklist);
                break;
            case 4:
                deleteBook(booklist);
                break;
            case 5:
                booklist.traverse();
                break;
            default:
                break;
        }
        choice = getUserChoice(); // prompt user to enter the choice again

    return 0;
    }       
}   

，然后我的头文件保存为Program.h在同一文件夹中，代码如下

#ifndef PGM_03_H//<-
#define PGM_03_H//<- both these need to have the same name
#include <string>

using namespace std;
/*class definition for BookNode
 * which is non-compatible. i.e it has a pointer to the next BookNode
 */

class BookNode{
    private : 
        std::string bookTitle;
        BookNode * next;
    public : 
        //default constructor
        BookNode(){bookTitle = "";next = NULL;} 
        //custom constructor
        //it initializes book with title        
        BookNode(string title){
            bookTitle = title;
            next = NULL;
        }
        //getter functions
        std::string getTitle(){
            return bookTitle;
        }
        BookNode * getNext(){
            return next;
        }
        //setter functions
        void setTitle(std::string newTitle){
            bookTitle = newTitle;
        }
        void setNext(BookNode * newNext){
            next = newNext;
        }
};

/*
* class definition for BookList
* which is a linked list that uses object of BookNode as node.
* it has only one variable: head, which is a BookNode pointer.
*/
class BookList{
    private:
        BookNode * head;

    public:
        //default constructor
        BookList(){
            head = NULL;
        }

        //destructor, which will be called automatically
        //it deletes all nodes in the linkedlist
        ~BookList();
        //add new node as the first node in the booklist
        void addFirst(BookNode *);

        //add new node as the last node in the booklist
        void addLast(BookNode *);

        //traverse function. It will print out info on BookNode
        void traverse();

        //check if the given book is in the list
        bool isInTheList(std::string);
        //delete the given book
        //return true if it was deleted
        //return false if it was not found
        bool deleteBook(std::string);

};


#endif