엑세스 위반 발생 오류 도와주세요ㅠㅠ

using namespace std;
#include <string>
 
class Stuff{
private:
	string _name;
	int _price;
	int _stock;
	int _discount;
	int _discountStock;
public:
	Stuff();
	Stuff(string name, int price, int stock);
	~Stuff();
 
	void SetStuff(string name, int price, int stock);
	void SetDiscount(int discount, int discountStock);
	string nameShow();
	int priceShow();
	int stockShow();
	int discountShow();
	int discountStockShow();
 
};
 
#endif

#ifndef SHOPLIST_H
#define SHOPLIST_H
#include <string>
#include "Stuff.h"
 
class Shoplist {
private:
	Stuff * _list;
	string _name;
	int _items;
public:
	Shoplist();
	Shoplist(string name);
	~Shoplist();
 
	void AddStuff(Stuff stuff);
	void RemoveStuff(int num);
	void listShow();
	void setDiscount(int standard, double rate, int stocks);
	string nameShow();
};
 
 
#endif

#include <iostream>
#include <string>
using namespace std;
#include "Stuff.h"
#include "Shoplist.h"
#define SIZE_OF_SHOPLIST 30
 
void Shoplist::AddStuff(Stuff stuff) {
	_list[_items] = stuff;
	this->_items++;
}
 
void Shoplist::listShow() {
	cout << "--------------------------------------------------\n";
	cout << _name << endl;
	cout << "--------------------------------------------------\n";
	cout << "순번" << '\t' << "이름" << '\t' << "가격" << '\t' << "재고" << '\t' << "할인가격" << '\t' << "할인 상품 재고" << endl;
	if (_items == 0) {
		return;
	}
	for (int i = 0; i < _items; i++) {
		if(_list[i].discountShow() != 0 && _list[i].discountStockShow() != 0){
			cout << i + 1 << "." << '\t' << _list[i].nameShow() << '\t' << _list[i].priceShow() << '\t' << _list[i].discountShow() << '\t' << _list[i].discountStockShow() << endl;
		}
		else{
			cout << i + 1 << "." << '\t' << _list[i].nameShow() << '\t' << _list[i].priceShow() << endl;
		}
	}
}

#include <iostream>
#include <string>
using namespace std;
#include "Stuff.h"
#include "Shoplist.h"
 
 
int findList(string name, Shoplist catalog[], int size) {
	for (int i = 0; i < size; i++) {
		if (catalog[i].nameShow() == name) {
			return i;
		}
	}
}
 
 
int main(){
  //중략
 
	int what_to_do;
	string list_name;
	int a;
	double discount_rate;
	int stuff_num, discount_price, discount_stock;
 
	while (1) {
		for (int i = 0; i < num_list; i++) {
			catalog[i].listShow();
		}
 
		cout << "작업하고자 하는 리스트의 이름을 입력하시오: ";
		cin >> list_name;
		a = findList(list_name, catalog, num_list);
		cout << "\n원하는 작업을 입력하세요.\n" << "1. 항목 추가   2. 항목 삭제   3. 할인율 적용   Q.종료:::: ";
		cin >> what_to_do;
 
		switch (what_to_do) {
		case 1: {
			string stuff_name;
			int stuff_price, stuff_stock;
 
			cout << "이름: ";
			cin >> stuff_name;
			cout << "가격: ";
			cin >> stuff_price;
			cout << "재고: ";
			cin >> stuff_stock;
			Stuff addstuff(stuff_name, stuff_price, stuff_stock);
			catalog[a].AddStuff(addstuff); }
			break;
 
		//중략
		}
 
	}
 
	return 0;
 
return 0;
}