C语言问题，求大神解答

//Node* head表示头指针

//头指针指向头结点，头结点的值无用，头结点的指针指向链表内第一个元素

//当NULL == head->next时链表为空，当NULL == head时链表为无效链表

#include

#include

typedef struct Node {

int val;

struct Node* next;

}Node;

void* _malloc(size_t size) {

void* res = malloc(size);

if (NULL == res) {

printf("内存不足，程序正在退出\n");

exit(1);

}

return res;

}

void Append(Node* node, int val) {

Node* next = node->next;

node->next = _malloc(sizeof(Node));

node->next->val = val;

node->next->next = next;

}

void SortInsert(Node* head, int val) {

if (NULL != head) {

Node* last;

for (;;) {

last = head;

head = head->next;

if (NULL == head || head->val >= val) {

break;

}

}

Append(last, val);

}

}

void EraseP(Node* last) {

if (NULL != last && NULL != last->next) {

Node* next = last->next->next;

free(last->next);

last->next = next;

}

}

void Erase(Node* head, int n) {

while (n-- > 0 && NULL != head) {

head = head->next;

}

if (NULL != head) {

EraseP(head);

}

}

void ShowAll(Node* head) {

if (NULL != head) {

while (NULL != (head = head->next)) {

printf("%d -> ", head->val);

}

printf("\n");

}

}

int main(int argc, char* argv[]) {

Node* head = _malloc(sizeof(Node));

head->next = NULL;

SortInsert(head, 4); ShowAll(head);

SortInsert(head, 0); ShowAll(head);

SortInsert(head, 1); ShowAll(head);

SortInsert(head, 3); ShowAll(head);

SortInsert(head, 2); ShowAll(head);

printf("\n");

Erase(head, 3); ShowAll(head);

Erase(head, 3); ShowAll(head);

Erase(head, 0); ShowAll(head);

Erase(head, 1); ShowAll(head);

Erase(head, 0); ShowAll(head);

return 0;

}

运行截图