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Exception thrown in linked list

F95 (64)
When I compile and run my code, everything works fine if the first input is 'E'. If my first input is 'D', the compiler closes and I get an exception thrown (read access violation. this->head was nullptr. If there is a handler for this exception, the program may be safely continued.) If you look at void Airlines::displayReservation() I have it set up so that clicking 'D' as a first action will tell the user that the node is null, and up until I finished making modification it was working, now it isn't.

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#pragma once
#include <iostream>
using std::cout;
using std::cin;
using std::endl;
using std::system;

const int NAME = 50;
const int LEN = 3;

class Airlines
{
	struct ListNode
	{
		char	FName[NAME];
		char	LName[NAME];
		char 	Priority;
		int		FltNum;

		ListNode* next;
		ListNode()
		{
			strcpy_s(FName, "");
			strcpy_s(LName, "");
			Priority = 0;
			FltNum = 0;
			next = NULL;
		}
	};
	ListNode* head;
public:
	Airlines() { head = NULL; }
	ListNode pass;
	void appendNode();
	void displayReservation();
}; 

#include "Airline.h"

void Airlines::appendNode()
{
	ListNode* newNode, *nodePtr;
	newNode = new ListNode;
	cout << "Enter your first name\n";
	cin.ignore();
	cin.getline(newNode->FName, NAME);
	
	cout << "Enter your last name\n";
	cin.getline(newNode->LName, NAME);

	cout << "Enter your flight number\n";
	cin >> newNode->FltNum;

		cout << "Enter a boarding Priority\n";
		cout << "(P)latinum, (G)old, (S)ilver, or (L)ead\n";
		cin>>newNode->Priority;
		
	if (!head)
			head = newNode;
		else
		{
			nodePtr = head;
			while (nodePtr->next != NULL)
				nodePtr = nodePtr->next;
			nodePtr->next = newNode;
		}
}


void Airlines::displayReservation()
{
	ListNode* nodePtr = head->next;
	nodePtr = head;
	if (nodePtr == NULL)
		cout << "Your list is empty\n";
	else
	{
		while (nodePtr)
		{
			cout << "First Name: " << nodePtr->FName<< endl;
			cout << "Lirst Name: " << nodePtr->LName << endl;
			cout << "Flight Number: " << nodePtr->FltNum << endl;
			if ((nodePtr->Priority == 'P') || (nodePtr->Priority == 'p'))
				cout << "Your boarding priority is Platinum\n";
			else if ((nodePtr->Priority == 'G') || (nodePtr->Priority == 'g'))
				cout << "Your boarding priority is Gold\n";
			else if ((nodePtr->Priority == 'S') || (nodePtr->Priority == 's'))
				cout << "Your boarding priority is Silver\n";
			else
				cout << "Your boarding priority is Lead\n";
			nodePtr = nodePtr->next;
		}
	}
}

int main()
{
	Airlines list;
	char prompt;
	char loop = 'y';
	do
	{
		cout << " AIRLINE RESERVATION SYSTEM \n";
		cout << "Press (E) to Enter passenger flight information " << endl;
		cout << "Press (D) to Display the passenger flight information " << endl;
		cout << "Press (Q) to Quit the program " << endl;
		cin >> prompt;

		switch (prompt)
		{
		case 'E':
		case 'e':
			list.appendNode();
			break;

		case 'D':
		case 'd':
			list.displayReservation();
			cout << endl;
			break;

		case 'Q':
		case 'q':
			loop = 'n';
			cout << "\nExiting the program..\n";
			break;

		default: cout << "this is an invalid choice. Please select prompt from the menu.\n";
		}system("pause");
	} while ((loop == 'Y') || (loop == 'y'));

	return 0;
}


also,in the void Airlines::appendNode(), I originally had the code written as such to account for an incorrect letter typed:
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do 
{
        cout << "Enter a boarding Priority\n";
	cout << "(P)latinum, (G)old, (S)ilver, or (L)ead\n";
	cin>>newNode->Priority;
}while((newNode->Priority != 'p') || (newNode->Priority != 'P') ||(newNode->Priority != 'g') || (newNode->Priority != 'G') ||(newNode->Priority != 's') || (newNode->Priority != 'S') || (newNode->Priority != 'l') || (newNode->Priority != 'L'))

the problem with this was that when I ran it, I would get an endless loop despite entering a 'p' 'g' 's' or 'l'. Is there another way to rewrite this to that will accomplish what I am trying to do?(adding in a system("cls") would also be helpful).
Last edited on
coder777 (8444)
I would get an endless loop despite entering a 'p' 'g' 's' or 'l'.
The problem is that you use || in your expression for the while loop. It is guaranteed that one of the or'd expression is true. So replace || with &&.
F95 (64)
Thanks. Everything works now. I also figured out why the exception was being thrown. This is what the instructor was looking for with the only note they added being //Need a blank line between passenger outputs 
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#pragma once
#include <iostream>
using std::cout;
using std::cin;
using std::endl;
using std::system;

const int NAME = 50;

class Airlines
{
	struct ReservationNode
	{
		char	FName[NAME];
		char	LName[NAME];
		char 	Priority;
		int	FltNum;

		ReservationNode* next;
		ReservationNode()
		{
			strcpy_s(FName, "");
			strcpy_s(LName, "");
			Priority = 0;
			FltNum = 0;
			next = NULL;
		}
	};
	ReservationNode* head;
public:
	Airlines() { head = NULL; }
	void appendNode();
	void displayReservation();
};
#include "Airline.h"


void Airlines::appendNode()
{
	ReservationNode* newNode, *nodePtr;
	newNode = new ReservationNode;
	cout << "Enter your first name\n";
	cin.ignore();
	cin.getline(newNode->FName, NAME);

	cout << "Enter your last name\n";
	cin.getline(newNode->LName, NAME);

	cout << "Enter your flight number\n"; //also would've been useful to find a 
	cin >> newNode->FltNum;            
	do
	{
	cout << "Enter a boarding Priority\n";
	cout << "(P)latinum, (G)old, (S)ilver, or (L)ead\n";
	cin >> newNode->Priority;
	} while ((newNode->Priority != 'p') && (newNode->Priority != 'P') && (newNode->Priority != 'g') && (newNode->Priority != 'G') && (newNode->Priority != 's') && (newNode->Priority != 'S') && (newNode->Priority != 'l') && (newNode->Priority != 'L'));

	if (!head)
		head = newNode;
	else
	{
		nodePtr = head;
		while (nodePtr->next != NULL)
			nodePtr = nodePtr->next;
		nodePtr->next = newNode;
	}
	system("cls");
}


void Airlines::displayReservation()
{
	ReservationNode* nodePtr;
	nodePtr = head;

	if (nodePtr != NULL)
	{
		cout << "------------------------------------------\n";
		cout << "       Passenger Reservation Info        \n";
		cout << "------------------------------------------\n";
		while (nodePtr)
		{
			cout << "First Name: " << nodePtr->FName << endl;
			cout << "Lirst Name: " << nodePtr->LName << endl;
			cout << "Flight Number: " << nodePtr->FltNum << endl;
			if ((nodePtr->Priority == 'P') || (nodePtr->Priority == 'p'))
				cout << "Your boarding priority is Platinum\n";
			else if ((nodePtr->Priority == 'G') || (nodePtr->Priority == 'g'))
				cout << "Your boarding priority is Gold\n";
			else if ((nodePtr->Priority == 'S') || (nodePtr->Priority == 's'))
				cout << "Your boarding priority is Silver\n";
			else
				cout << "Your boarding priority is Lead\n";
			nodePtr = nodePtr->next;
		}
	}
	else
		cout << "Empty List. Please Enter Reservation Information..\n";
}

int main()
{
	Airlines list;
	char prompt;
	char loop = 'y';
	do
	{
		cout << "-------------------------------------------\n";
		cout << "           RESERVATION SYSTEM           \n";
		cout << "-------------------------------------------\n";
		cout << "Press (E) to Enter passenger flight information " << endl;
		cout << "Press (D) to Display the passenger flight information " << endl;
		cout << "Press (Q) to Quit the program " << endl;
		cin >> prompt;

		switch (prompt)
		{
		case 'E':
		case 'e':
			list.appendNode();
			break;

		case 'D':
		case 'd':
			list.displayReservation();
			cout << endl;
			break;

		case 'Q':
		case 'q':
			loop = 'n';
			cout << "\nExiting the program..\n";
			break;

		default: cout << "this is an invalid choice. Please select prompt from the menu.\n";
		}system("pause");
	} while ((loop == 'Y') || (loop == 'y'));

	return 0;
}
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