project.exe вызвал точку останова

У меня был круговой список ссылок, в котором есть функции добавления, удаления, печати, поиска и т. Д. Все функции работают правильно, но когда я удаляю все узлы в списке и пытаюсь добавить новые узлы в тот же список, я получаю, что project.exe имеет вызвало сообщение о точке останова.

list.h

#ifndef LIST_H
#define LIST_H

using namespace std;

class list {
public:

struct node {
string data, assignee, date;
node *next;
};

typedef struct node NodePtr;

NodePtr *head, *current, *temp, *dummy;

list();
void add();
void del();
void printList();
void menu();
void exit();
void search();

};

#endif

Source.cpp

#include <cstdlib>
#include <iostream>
#include "List.h"#include<string>

using namespace std;

list::list() {          //constructor
head = NULL;
current = NULL;
temp = NULL;
}
void list::add(){
string addTask, addAssignee, addDate;
NodePtr *newNode = new NodePtr;

//entering the data of the tasks
cout << "Enter the name of the task:\n"<<"<<";
getline(cin, addTask);          // compailer doesnt detect the first getline   function, ı dont understan why. ı had to put it twice
getline(cin, addTask);
cout << "Enter the assignee name for the task:\n" << "<<";
getline(cin, addAssignee);
cout << "Enter the deadline for the task:\n" << "<<";
getline(cin, addDate);
cout << "\n";

//assignt data to the new node
newNode->data = addTask;
newNode->assignee = addAssignee;
newNode->date = addDate;
newNode->next = NULL;

if (head != NULL){

current = head;

while (current->next != head){          //finding the last node
current = current->next;
}
current->next = newNode;
dummy = newNode;
dummy->next = head;             //  we make the list, circular
}
else               //here will work if the list is empty
{
head = newNode;
dummy = newNode;
head->next=head;
}}
void list::printList(){
int i = 1;
current = head;
if (head == NULL){
cout << "List is empty\n\n";
}
else
{
do
{
cout << i << "-";
cout << current->data << endl;
cout << current->assignee << endl;
cout << current->date << endl << endl;
current = current->next;
i++;
} while (current != dummy->next);
}
}

void list::del(){                       //tüm liste silindikten sonra tekrar işlem(ekleme, listeleme etc.) yapılamıyor hata veriyor
NodePtr *delPtr;
delPtr = NULL;
int ID;
cout << "These tasks exist in the list:\n";
printList();
cout << "Choose the ID of the task you want to remove:\n";
cin >> ID;
if (head == NULL){
cout << "List does not includes any task.\n";
}
else
if (ID == 1){
delPtr = head;
head = head->next;
delete delPtr;
dummy->next = head;
}
else
{
current = head;

for (int k = 1; k <= ID - 1; k++){
temp = current;
current = current->next;
}
if (current == dummy){
dummy = temp;
dummy->next = head;
}
delPtr = current;
current = current->next;
temp->next = current;

delete delPtr;
}
}
void list::menu(){

cout << "Choose an operation\n"<< "A: Add Task\n"<< "S: Search for Task\n"<< "L: List All Tasks\n"<< "R: Remove Task\n"<< "E: Exit\n\n"<<"<<";

}

void list::search(){
string searchTask;
NodePtr *search;
search = head;

cout << "To search for a task, enter its task name or assignee name:\n" << "<<";
getline(cin, searchTask);
getline(cin, searchTask);

while (search != dummy){//bu satır problemli gibi gözüküyor

if (search->data == searchTask || search->assignee == searchTask){
cout << search->data << endl
<< search->assignee << endl
<< search->date << endl<<endl;
}
search = search->next;
}

}

void list::exit(){
node *delPtr;
current = head;
if (head != NULL){

do{
temp = current;
delPtr = temp;
current = current->next;

delete delPtr;
} while (current != dummy);
}
}

main.cpp

#include <cstdlib>
#include <iostream>
#include "List.h"#include<string>
using namespace std;

int main(){char operation;
list tasks;
tasks.menu();cin >> operation;

while (operation!='E' && operation!='e'){

switch (operation)
{
case 'A':case'a':
tasks.add();
break;
case 'S': case's':
tasks.search();
break;
case 'L': case 'l':
cout << "All tasks are listed below:\n";
tasks.printList();
break;
case 'R': case 'r':
tasks.del();
break;
default:
break;
}
tasks.menu();
cin >> operation;}

tasks.exit();
return 0;
}