How to insert integers number to doubly linked list from a text file

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C++

This's program will display the integers numbers from the text file

1 2 3 4 5 6


and ask the user to

1- Add a number "
2- Delete a number from the list \n";
3- Show the list.

Can someone help me to implement the following step:
1- How to insert the integers numbers from the text file to the doubly linked list.
1- if the user added a number, the number should be added to the text file.
2- if the user delete a number, the number should be deleted from the text file.

#include <iostream>
#include <string>
#include <fstream>

using namespace std;
struct  node
{
	int number; 
	node *next; 
	node *prev; 
}*start;

class double_llist
{
public:
	bool isEmpty(node *head);
	char menu();
	void insertAsFirstElement(node *&head, node *&last, int number);
	void inser(node*&head, node*&last, int number);
	void remove(node *&head, node *&last);
	void showlist(node *current);
	int numIntElement(ifstream&x);
private:

};

int main() {

	string filename;
	cout << " Please enter the name of the file = "; 
	cin >> filename; 
	ifstream myfile; 
	myfile.open(filename); 
	if (!myfile.is_open()) {
		cout << endl << " failed to open file, check that it exists and you have access \n" << "\n" << endl; 

	}
	else if (myfile.is_open())
	{
		ifstream x;
		double_llist dl;
		dl.numIntElement(x); 
		int int1 = 0; 
		cout << " File exists \n";

		////
		node * head = NULL;
		node *last = NULL;
		char choice;
		int number;
		do {
			choice = dl.menu();
			switch (choice)
			{
			case '1':
				cout << " Please enter number : ";
				cin >> number;
				dl.inser(head, last, number);
				break;
			case '2':
				dl.remove(head, last);
			case '3':
				dl.showlist(head);
				break;
			default:
				break;
			}
		} while (choice != '4');
		{

		}
	}
	
	system("pause");
	return 0; 
}
int double_llist::numIntElement(ifstream&x) {

	int n = 0;
	int m; 
	ifstream myfile("file.txt");
	int countsingfie = 0;

	while (!myfile.eof())
	{
		myfile >> n;
		//if (countsingfie == 0) {
		//	cout << "Error : file exist but no data " << endl;
		//}
		cout << "The numbers in the file are  " << n<< "" << endl;
	}
	return countsingfie;
}
bool double_llist::isEmpty(node *head) {
	if (head == NULL) {
		return true; 
	}
	else
	{
		return false;
	}
}
char double_llist::menu() {
	char choice; 
	cout << " Main Menu \n"; 
	cout << " 1 . Add a number \n";
	cout << " 2 . Delete a number from the list \n";
	cout << " 3 . Show the list \n"; 
	cout << " 4.  Exit \n";
	cin >> choice; 
	return choice;
}
void  double_llist::insertAsFirstElement(node *&head, node *&last, int number) {
	node *temp = new node; 
	temp->number = number; 
	temp->next = NULL; 
	head = temp; 
	last = temp; 
}
void double_llist::inser(node*&head, node*&last, int number) {
	if (isEmpty(head)>0){
		insertAsFirstElement(head, last, number); 
	}
	else if (isEmpty(head) < 0)
	{
		cout << " Please enter a number above 0 " << endl;
	}
	else
	{
		node *temp = new node;
		temp->number = number;
		temp->next = NULL;
		last->next = temp;
		last = temp;
	}
}
void  double_llist::remove(node *&head, node *&last) {
	if (isEmpty(head)) {
		cout << " Sorry, The list is already empty \n"; 

	}
	else if (head == last)
	{ 
		delete head; 
		head = NULL;
		last = NULL; 

	}
	else
	{
		node *temp = head; 
		head = head->next; 
		delete temp; 
	}
}
void double_llist::showlist(node *current) {

	if (isEmpty(current)) {
		cout << " The list is empty \n";
	}
	else
	{
		cout << " The list contains: \n "; 
		while (current != NULL)
		{
			cout << current->number << endl; 
			current = current->next; 

		}
	}
}

What I have tried:

1- How to insert the integers numbers from the text file to the doubly linked list.
1- if the user added a number, the number should be added to the text file.
2- if the user delete a number, the number should be deleted from the text file.