利用链表实现对字母的插入、删除，错误是读取访问权限冲突，求问大佬这是指针的问题吗，请各位大佬帮忙修改（问题在delete函数星号内部）

#include<iostream>
#include<stdlib.h>
#include<malloc.h>
using namespace std;

typedef struct node
{
    char data;
    struct node* next;
}node, * pnode;

pnode create_list()
{
    int i;
    pnode head = (pnode)malloc(sizeof(node));
    if (!head)
    {
        cout << "未成功分配内存" << endl;
        exit(-1);
    }
    pnode p = head;
    for (i = 0; i < 25; i++)
    {
        p->data = 'A' + i;
        p->next = (pnode)malloc(sizeof(node));
        if (!p->next)
        {
            cout << "未成功分配内存" << endl;
            exit(-1);
        }
        p = p->next;
    }
    p->data = 'A' + 25;
    p->next = NULL;
    return head;
}
int show_list(pnode p)
{
    while (p!= NULL)
    {
        cout << p->data << '-' << '>';
        p = p->next;
    }
    if (p== NULL)
    {
        cout << "NULL" << endl;
    }
    return 0;
}
int insert_list(pnode p)
{
    char a;
    cin >> a;
    pnode pnew = (pnode)malloc(sizeof(node));
    if (!pnew)
    {
        cout << "内存未分配成功" << endl;
        exit(-1);
    }
    pnew->data = a;
    pnew->next = NULL;
    while (p != NULL)
    {
        if (p->data != a)
        {
            cout << "wrong" <<endl;
            p = p->next;
        }
        else
        {
            pnew->next = p->next;
            p->next = pnew;
            break;
        }
    }
    return 0;
}
int delete_list(pnode p)
{
    char a;
    cin >> a;
    pnode q;
    q = NULL;
    while (p != NULL)
    {
        if (p->data != a)
        {
            cout << "wrong" << endl;
            q = p;
            p = p->next;
        }
****if (p->data == a)****
        {
            q->next= p->next;
            free(p);
        }
    }
    return 0;
}
int main()
{
    pnode phead;
    phead=create_list();
    show_list(phead);
    insert_list(phead);
    show_list(phead);
    delete_list(phead);
    show_list(phead);
    return 0;
}