VS历遍链表时读取访问权限冲突

Question

先谢谢各位大佬
我搜了一些资料，知道是因为ptr是NULL才会出现这种情况（应该吧）但是不知道怎么改，求救
先上码

#include <iostream>
using namespace std;

typedef struct node {
    int xishu;
    int zhishu;
    node* next;
}node;
node *start1 = NULL;
node *start2 = NULL; 
node *create1(struct node *);
node *create2(struct node *);
node *add(struct node*);
node *display(struct node*);

int main()
{
    create1(start1);
    //create1(start2);
    display(start1);
}

node* create1(struct node* start)
{
    struct node* ptr, * new_node;
    int coefficient, index;
    /×art = new node;
    cout << "Enter 0 to end when you entering coefficient"<<endl;
    cout << "Enter the coefficient and index"<<endl;
    cin >> coefficient;
    cin >> index;
    //new_node = new node;
    
    while (coefficient != 0) {
        new_node = new node;
        new_node -> xishu = coefficient;
        new_node -> zhishu = index;
        if (start == NULL)
        {
            new_node -> next = NULL;
            start = new_node;
        }
        else {
            ptr = start;
            while (ptr->next != NULL)
                ptr = ptr->next;
            ptr->next = new_node;
            new_node->next = NULL;

        }
        cout << "Enter the coefficient and index" << endl;
        cin >> coefficient;
        cin >> index;
    }
    return start;


}

node *display(struct node *start) 
{
    struct node* ptr;
    ptr = start;
    while (ptr != NULL);
    {
        cout << ptr->xishu << "x^" << ptr->zhishu << endl;
        ptr->next = ptr;
    }
    return start;

}

问题如下

Answer 1

报错的下一行改为ptr=ptr->next;循环的指针移动语句写反啦