Run time error in linkList attemp

there is this run time error that i just don't know how to fix. basically, i'm trying to make a shopping list using linkList. but a run time error has occur in my program. can someone please spot the mistake that i made. thx !

Code:

#include <iostream>
#include <string>

using namespace std;

class shopChart
{
	public:
	
		shopChart();
		void addItem (int itemID, string itemName, string itemPrice);
		void display ();
		~shopChart ();
	
	private:
	
	struct shopList
	{
		int ID;
		string price;
		string name;
		shopList *link;
	
	};

	shopList *list;
	
};

shopChart::shopChart ()
{
	list = NULL;
}

void shopChart::addItem (int itemID, string itemName, string itemPrice)
{
	shopList *item, *temp;
	
	if ( list = NULL )
	{
		list = new shopList;
		list -> ID = itemID;
		list -> price = itemPrice;
		list -> name = itemName;
		list -> link = NULL;
	}
	
	else
	{
		item = list;
		
		while (item -> link != NULL){
		
			item = item -> link;
			}
			
			
			temp = new shopList;
			temp -> ID = itemID;
			temp -> name = itemName;
			temp -> price = itemPrice;
			temp -> link = NULL;
			item -> link = temp;
	}
}

void shopChart::display()
	
{

	shopList *x;
	cout<<endl;
	
	for (x = list; x != NULL; x = x -> link)
	{
		cout<< "Item ID : \t"<< x->ID <<endl;
		cout<< "item Name : \t"<< x->name <<endl;
		cout<< "item price : \t"<< x->price <<endl;
	}
}

shopChart::~shopChart()
{

	shopList *x;
	
	if ( list == NULL )
	{
		return;
	}
	
	while ( list != NULL )
	{
	
		x = list -> link;
		delete list;
		list = x;
	}

}

int main ()
{

	shopChart chart;
	chart.addItem(1, "meja", "100.000");
	chart.addItem(2, "kursi", "1000.000");
	
	chart.display();
	
	getchar();
	return 0;

}

Code:

if ( list = NULL )

This looks rather suspect to me.

Also, unless it is an exercise, there's no reason to code linked lists yourself, since the standard library has a selection of container available.