引发了未经处理的异常:读取访问权限冲突。 **p** 是 nullptr？

Question

大佬们救救。

写个链式表多项式，老是填一些奇怪的错误，能帮忙看看吗

#include <stdio.h>
typedef int datatype;
#include <stdlib.h>
#define NULL 0
typedef struct node
{
	datatype xi;
	datatype zhi;
	struct node* next;
}node;
void init(node** head) {
	*head = (node*)malloc(sizeof(node));
	(*head)->next = NULL;
}
int length(node* head) {
	node* p; int n = 0;
	p = head;
	while (p->next) {
		p = p->next;
		n++;
	}
	return n;
}
node* insert(node* head, int i, datatype xi,datatype zhi) {
	int j = 0;
	node* p;
	init(&p);
	p = head->next;
	//j计数
	//i是表示插入的位置
	if (!p) {
	}
	while (j < i - 1 && p->next != NULL) {
		p = p->next;
		j = j++;
	}
	if (j == i - 1) {
		node* q = (node*)malloc(sizeof(node));
		init(&q);
		q->xi = xi;
		q->zhi = zhi;
		q->next = p->next;
		p->next = q;
		return head;
	}
}
int find(node* head, int i, datatype* x,datatype*y) {
	int j = 0;
	node* p = head->next;
	while (j < i && p->next != NULL) {
		j = j++;
		p = p->next;
	}
	if (j == i) {
		*x = p->xi;
		*y = p->zhi;		
		return 1;
	}
	return 0;
}
node* deleted(node* head, int i) {
	node* p = head->next;
	int j = 0;
	while (j < i - 1 && p->next != NULL) {
		j = j++;
		p = p->next;
	}if (j == i - 1) {
		p->next = (p->next)->next;
		return head;
	}
}
/*node* sort(node* head1) {
	node* p;
	node* q;
	int j=0;
	int i = length(head1);
	int k;
	init(&p); 
	init(&q);
	for (k = 1; i-1;k++) {
		q = head1->next;
		while (j < i && q->next != NULL) {
			if (q->zhi < (q->next)->zhi) {
				p->next = q->next;
				q->next = q;
				q = p;
			}
			j = j++;
			p = p->next;
		}
	}
	return head1;
}
int sum(node* head1, node* head2) {
	node* head3;
	node* p;
	node* q;
	init(&p);
	init(&q);
	init(&head3);
	int i, j, len1, len2 = 0;
	int count = 1;
	p = head1->next;
	q = head2->next;
	len1 = length(p);
	len2 = length(q);
		for (j = 0; j <= len1; j++) {
			for (i = 0; i <= len2; i++) {
				if (p->zhi = q->zhi)
				{
					head3->xi = p->xi +q->xi;
					head3->zhi = p->zhi;
					head3 = head3->next;
					p = p->next;
					q = q->next;
				}
				else
				{
					head3 = p;
					head3 = head3->next;
					head3 = q;
					head3 = head3->next;
					p = p->next;
					q = q->next;
				}
			}
		}
		sort(head3);
		int len3 = length(head3);
		int x, y;
		for (i = 1; len3; i++) {
			find(head3, i, &x, &y);
			printf("%5dx^%d", x, y);
			if (i < len3)
			{
				printf("    +");
			}
		}
		return 1;
}

int subtract(node* head1, node* head2) {
	node* head3;
	node* p;
	node* q;
	init(&p);
	init(&q);
	init(&head3);
	int i, j, len1, len2 = 0;
	int count = 1;
	p = head1->next;
	q = head2->next;
	len1 = length(p);
	len2 = length(q);
	for (j = 0; j <= len1; j++) {
		for (i = 0; i <= len2; i++) {
			if (p->zhi = q->zhi)
			{
				head3->xi = p->xi + q->xi;
				head3->zhi = p->zhi;
				head3 = head3->next;
				p = p->next;
				q = q->next;
			}
			else
			{
				head3 = p;
				head3 = head3->next;
				head3 = q;
				head3 = head3->next;
				p = p->next;
				q = q->next;
			}
		}
	}
	sort(head3);
	int len3 = length(head3);
	int x, y;
	for (i = 1; len3; i++) {
		find(head3, i, &x, &y);
		printf("%5dx^%d", x, y);
		if (i < len3)
		{
			printf("    +");
		}
	}
	return 1;

}*/
int main() {
	node* head1;
	node* head2;
	int len, x,y;
	init(&head1);
	init(&head2);
	len = length(head1);
	printf("%5d\n", len);
	insert(head1, 1, 3, 3);
	insert(head1, 2, 5, 2);
	insert(head1, 3, 8, 1);
	printf("%5d\n", length(head1));
	for (int i = 1; i <= length(head1); i++) {
		find(head1, i, &x,&y);
		printf("%5dx^%d", x,y);
		if(i<length(head1))
		{
			printf("    +");
		}
	}
	printf("\n");
	insert(head2, 1, 3, 4);
	insert(head2, 2, 8, 1);
	insert(head2, 3, 6, 3);
//	sort(head2);
	for (int i = 1; i <= length(head2); i++) {
		find(head2, i, &x, &y);
		printf("%5dx^%d", x, y);
		if (i < length(head2))
		{
			printf("    +");
		}
	}

}



/*1234

2134
2314
2341

3241
3421
3421

4321
4321
4321
*/

爆这个错误

Answer 1

解决了么，我也出现了这样的错