C++ linked list and objects

[soil]

I have been given an assignment from my uni to create a bank where im to have customers with multiple accounts and different account types, also then add other things like loans etc.

Im having problems getting a linked list to work with the class objects. my aim is to store all the customers details, and account details in the class objects then list all the customers in the linked list instead of using something like an array as we get more marks for using linked lists.

so far i have managed to get it so the customer can be created and pointing to just one account. but i am stuggling with understanding how im to then create the linked list so it connects to the class object.

these are some bits of the code which i have so far:

AssignmentBank.cpp (main)

	Account tempAccount(001, 500, 600, "Current");
	Customer tempCustomer("Fred", 01, 0.5, 'M',"180690", &tempAccount);
	CustomerList CL;	
	CL.addCustomer(&tempCustomer);

with this im not sure if im doing it the correct way, but am i to create the objects then pass in the refference to it, which is then stored in the linked list?

CustomerList.cpp

#include "CustomerList.h"
#include <iostream>

using namespace std ;

CustomerList::CustomerList()
{
    front = back = 0;
}

bool CustomerList::isEmpty()
{
   return front == 0;
}


void CustomerList::addCustomer(Customer *tempCustomer)
{
	Node* insert  = new Node(tempCustomer); 
	if (front == 0)
   {
      back = front = insert;
   }
   else
   {
      back-> next = insert ;      
	   back = back -> next ;
   }
}

CustomerList::removeCustomer()
{
   Customer tempCustomer; Node* temp;

	if (front != 0)
   {
      tempCustomer = front -> customerRef;
      temp = front;
      front = front -> next ;
      delete temp ;
      if (front == 0) back = 0;
      return tempCustomer;
   }
   else return '\0';

}


CustomerList::~CustomerList()
{
   Node * temp;
	while(front != 0)
	{
		temp = front;
		front = front -> next;
		delete temp;  
	}
}


void CustomerList::print()
{
	Node * temp = front;
   if (temp != 0 ) 
   {
	   while (temp != 0)
	   {
		   cout << temp -> customerRef.getName() ;
		   temp = temp -> next;
      }
   }
   else cout << "empty";
   cout << endl;

}

CustomerList.h

#include "Customer.h"

class Node
{
public:
	Node* next;
	Customer customerRef;
	Node(tempCustomer)
	{
		Customer *tempCustomer;
		next = 0;
	}	
};


class CustomerList
{
	Node* front;
        Node* back;
public:
	CustomerList();
	~CustomerList();
	void addCustomer(Customer *tempCustomer);
   removeCustomer( );
	bool isEmpty();
   void print() ;

};

any help at all would be useful.

I have gone to extra classes at uni and asked lecturers over and over but they dont seem to be helping me much.

[Andre S. Veteran]

The problem is your Node class: you have to decide whether you want it to hold copies of Customers or references(pointers) to Customers. Both approaches are valid yet different. If you go with references, you have to ensure that the original Customers remain alive otherwise the references will soon point to nothing. If you go with values (copies), there's no dangling reference issue but of course you encur the performance cost of the copy.

This is basically how I would code it:

struct Node // if you only want public members, use a struct, it's the same thing as class except everything is public by default
{
        Node* m_next;
        Customer& m_customer;
        Node(Customer& customer) : m_next(0), m_customer(customer) {}   
};

And then the addCustomer method would look virtually identical to yours (except I like references better when I can use them):

void CustomerList::addCustomer(Customer& customer)
{
    Node* insert  = new Node(customer); 
    if (front == 0)
   {
      back = front = insert;
   }
   else
   {
      back->next = insert;   
      back = back ->next;
   }
}

[soil]

how would i create it without using a struct?

i asked my lecturer about that the other day and he said "thats more of a C way of doing a linked list." and i should do it the way i've been trying to do it.

[Andre S. Veteran]

A struct is a class in C++. They are literally duplicate keywords. The only difference is that default visibility is private in a class, whereas it is public in a struct. So if all it takes to satisfy your teacher is to not use the keyword "struct", change "struct" by "class" and add "public:" before the member declarations. :laugh:

Seriously though, it's not clear to me what your teacher meant by that. The C++ way of doing a linked list is usually:

#include <list>

int main()
{
    // look ma no code
    std::list<int> linkedList;
    linkedList.push_back(1);
    // etc
}

[soil]

thank you, i got it working after playing around a little with what i already had. can now add customers and display them how i need to.

problem is now i want to be able to have multiple accounts for each customer.

at the moment i have:

customer.cpp

Customer::Customer(string tempName, string tempTelNo, double tempInterestRate, char tempSex, string tempDoB, Account *bankAccount)
{
	name=tempName;
	telNo=tempTelNo;
	interestRate=tempInterestRate;
	sex=tempSex;
	DoB=tempDoB;
	accountRef=bankAccount;
}

and an example of creating a customer is:

AssignmentBank.cpp

CL.addCustomer(new Customer("Fred", "01785211211", 0.5, 'M',"110284", new Account(002, 600, 700, "Current")));

thing is i want to be able to make lots of accounts without a limit really.

and if i go to the array option then i cant change the size of the array can i?

can someone point me in the right direction of how i can do this?

[+theblazingangel MVC]

You need a linked list structure for everything you need a list of - customers, accounts, etc. Rather than duplicating the linked list code for each type of list, look into templating!

When creating your new example customer, you'd do it something like:

Customer* custTmp = new Customer("Fred", "01785211211", 0.5, 'M', "110284");
CustTmp->addAccount(new Account(002, 600, 700, "Current"));
CustTmp->addAccount(new Account(003, 601, 701, "Current"));
//etc
CL.addCustomer(custTmp);
custTmp = 0; //no need to keep a copy of the pointer here in main(), the linked list has it and can handle freeing up memory when necessary, safer to disarm this!

[soil]

  On 23/11/2010 at 00:18, theblazingangel said:

You need a linked list structure for everything you need a list of - customers, accounts, etc. Rather than duplicating the linked list code for each type of list, look into templating!

When creating your new example customer, you'd do it something like:

Customer* custTmp = new Customer("Fred", "01785211211", 0.5, 'M', "110284");
CustTmp->addAccount(new Account(002, 600, 700, "Current"));
CustTmp->addAccount(new Account(003, 601, 701, "Current"));
//etc
CL.addCustomer(custTmp);
custTmp = 0; //no need to keep a copy of the pointer here in main(), the linked list has it and can handle freeing up memory when necessary, safer to disarm this!

I understand how to create them as you have mentioned, just not to sure how to add the references of the accounts to the customer.

[Mr aldo]

I haven't used C++ in quite some time, but when I did, I made an arraylist class. Just a doubly linked list... I found it pretty fun to make, and I put it on Google Code.

You can check out the adding method here, among many others: http://code.google.com/p/arraylist/source/browse/trunk/arraylist.cpp#119