Switch options are random and abruptly stops

Question

I'm a coding newbie and I've been lost to what my program is doing. Basically, my add() method abruptly stops when I call it by case 1, 3 times, and then it terminates the program when I want to add more student ID to my node. I'm at a loss and I have been trying to find out what's wrong. Any help would be appreciated!

#include <iostream>
using namespace std;

struct Node
{
    int ID;
    Node *next;
}; Node *head = NULL;

void Menu();
void Add();
void Delete();
void Search();
void Display();

int main()
{
    int Options = 0;
        cout << "Welcome to Student Records. Choose an option:\n"
             << "1.) Add student\n"
             << "2.) Delete student\n"
             << "3.) Search student\n"
             << "4.) Display list of students\n"
             << "5.) Exit\n\n";
        cout << "Input: ";
        cin >> Options;

        do{
        switch(Options)
        {
        case 1:
            Add();
            break;
        case 2:
            Delete();
            break;
        case 3:
            Search();
            break;
        case 4:
            Display();
            break;
        default:
            cout << "Operation terminated.";
        }

        cout << "\nWhat's next?\n";
        Menu();
        cin >> Options;
        }while(Options == 1 || Options == 2 || Options == 3 || Options == 4);

        cout << "Exit program?";

    return 0;
}//end main

void Menu()
{
        cout << "1.) Add student\n"
             << "2.) Delete student\n"
             << "3.) Search student\n"
             << "4.) Display list of students\n"
             << "5.) Exit\n\n";
}

void Add()
{
    int id;
    Node *node_new;
    Node *pointer;
    Node *lastNode = NULL;

    node_new = new Node;

    cout << "Enter 3-digit Student ID#: ";
    cin >> id;
    node_new -> ID = id;

    if (head == NULL) //if list is empty
    {
        head = node_new;
        node_new -> next = NULL;
    }

    else //if head is not NULL
    {
        pointer = head;
        lastNode = NULL;

        while(pointer -> ID < id && pointer != NULL)
        {
            lastNode = pointer;
            pointer = pointer -> next;
        }

        if (lastNode == NULL)
        {
            head = node_new;
            node_new -> next = pointer;
        }

        else
        {
            lastNode -> next = node_new;
            node_new -> next = pointer;
        }
    }
}

void Delete()
{
    int id;
    Node *pointer;
    Node *lastNode;

    cout << "Enter Student ID# you wish to delete: ";
    cin >> id;

    if (head == NULL)
    {
        cout << "The list is already empty.";
    }
    else if (head -> ID == id)
    {
        pointer = head;
        head = head -> next;
        delete pointer;
    }
    else
    {
        pointer = head;

        while(pointer -> ID != id && pointer != NULL)
        {
            lastNode = pointer;
            pointer = pointer -> next;
        }


        if(pointer == NULL)
            cout << "Student does not exist.";
        else
            lastNode -> next = pointer -> next;
            delete pointer;
    }
}

void Display()
{
    Node *pointer;

    pointer = head;

    do{
        if(pointer == NULL)
            cout << "The list is already empty!";
        else
        {
            cout << "Student ID# " << pointer -> ID << endl;
            pointer = pointer -> next;
        }
    }while(pointer != NULL);
}

void Search()
{
 int id;
 Node *pointer;

 pointer = head;

 cout << "Who do you want to search? Enter ID#: ";
 cin >> id;

do{

    if(pointer == NULL)
        cout << "Empty";
    else
    {
         cout << "ID: " << pointer -> ID << endl;
         pointer = pointer -> next;
    }


}while(pointer != NULL);

}