c语言写链表遇到问题

Question

c语言写链表遇到的问题，问题出在删除，但是不知道是什么原因

```c
#include <stdio.h>//双向链表
#include <stdlib.h>

typedef struct a {
    int n;
    struct a *last;
    struct a *next;
} link;
link *creat();
int add(link *p, int aim);
link *find(int a, link *p);
int print(link *p);
int del(link *p, int aim);

int main() {

    link *p;
    p = creat();
    add(p, 2);
    add(p, 4);
    print(p);
    del(p, 4);
    print(p);

}

link *creat() {
    link *p;
    p = (link *)malloc(sizeof(link));
    p->last = p;
    p->next = p;
    p->n = 0;
    return p;
}

int add(link *p, int aim) {
    link *pp, *s;
    pp = (link *)malloc(sizeof(link));
    pp->next = p->next;
    s = pp->next;
    s->last = pp;
    p->next = pp;
    pp->last = p;
    pp->n = aim;
    return 1;
}

link *find(int a, link *p) {
    link *pp;
    pp = p;
    do {
        if (pp->n == a)
            return pp;
        pp = pp->next;
    } while (pp != p);
    return NULL;
}

int del(link *p, int aim) {
    link *pp;
    pp = find(aim, p);
    printf("\n%d\n", pp->n);
    printf("\n%d\n", pp->last->n);
    if (pp = NULL) {
        return 0;
    } else {
        printf("问题没出\n");
        pp->last->next = pp->next;
        printf("问题没出\n");
        pp->next->last = pp->last;
        free(pp);
    }
    return 1;
}

int print(link *p) {
    link *pp;
    pp = p;
    int i = 0;
    do {
        i++;
        printf("%d\t", pp->n);
        pp = pp->next;
        if (i && i % 10 == 0)
            printf("\n");
    }    while (pp != p);
    return 1;
}

![img](https://img-mid.csdnimg.cn/release/static/image/mid/ask/672891620876110.png "#left")

Answer 1

“Devil组”引证GPT后的撰写：
问题似乎出在del()函数上。

这是有问题的一句话:

if (pp = NULL) {

变成双等于试试：

if (pp == NULL) {

还有

s = pp->next;
pp->next = p->next;

换成

pp->next = p->next;
s = pp->next;