Problem with a function

[Colox10]

I am trying to make the following work (firs the .h file followed by the problem):

The .h file:

#ifndef MYLIST_H
#define MYLIST_H

struct Air
		{
			string person;
			Air *next;
		};

class JGOp
{
	public:

		JGOp();// Constructor
		//~JGOp();//Destructor
		void InsertPassenger(); // Enters a passenger name.

	private:

		int size;
		//static const int MAXsize = 20;
		Air *head;
		//string person;
		string input;

};



#endif

The problem:

#include <iostream>
#include <cstdlib>
#include <string>
#include <iomanip>
#include <fstream>

using namespace std; 
using std::ostream;

#include "MyList.h"


JGOp::JGOp()
{ 
	size = 0; 
	head = NULL;

}

void JGOp::InsertPassenger()
{
	Air *ptr = new Air;
	cout << "Enter passenger: ";
	cin >> input;
    
	Add(input);	

}

void JGOp::Add(string input)
{
	Air *current = new Air;
	Air *ptr = new Air;
	Air *previous = new Air;
	ptr->person = input;

	if (head == NULL)
	{
		head = ptr->next;
	}
	current = head;
	previous = head;

	if(ptr->person < current->person)
	{
		current = previous->next;
		
		while (current != NULL && previous != NULL)
		{
			if(ptr->person < current->person)
			{
				ptr->next = current;
				previous->next = ptr;
			}
			current = current->next;
			previous = previous->next;
		}
                
	}

	else;

	current = head;
	previous = head;
	current = previous->next;

	while(current != NULL)
	{
		current = current->next;
		previous = previous->next;
	}

	previous->next = ptr;

}

Main:

#include <iostream>
#include <string>

using namespace std;

#include "MyList.h"


int main()
{
	JGOp JG;
	int choice, End;
	End = 1;	

	while (End != 0) 
	{
		
		cout << "Welcome to JetGreen Airlines, the Number #1 choice for" << endl;
		cout << "quality travel for Spring Break.\n"<< endl;

		cout << "Press 1 to reserve a flight on one of our luxurious aircrafts." << endl;
		cout << "Press 9 to exit our system." << endl << endl;

		cout << "What would you like to do?: ";
		cin >> choice;
		cout << "\n";

		switch (choice)
		{
			case 1:
				JG.InsertPassenger();
				/* Asks the user for passenger name and flight. It then adds the passenger
				   to the appropriate flight.*/				
				break;
				break;
			case 9:
				cout << "Thank you for choosing Jet Green!" << endl << endl ;
				End = 0;

		}     
	}

	return 0;
}

The point of this program is the following:
When the program loads, I want to put in a name, and have that name be saved to a string, which I can later print. The code complies, but once I run it, enter a passenger name, and press enter, I get an error. Can someone tell me what I am doing wrong here?