Switch options are random and abruptly stops - c++

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);
}