带头结点的链表

#include <stdio.h>
#include <stdlib.h>

struct node
{
    int num;

    struct node * next;
};

typedef struct node Node;
typedef struct node * Link;

void create_node(Link *new_node)
{
    int count = 10;

    do
    {
        *new_node = (Link)malloc(sizeof(Node));
        count--;
    }while(!is_malloc_ok(*new_node) && count);
}

int is_malloc_ok(Link new_node)
{
    if(new_node == NULL)
    {
        return 0;
    }
    return 1;
}

void create_link(Link *head)
{
    create_node(head);             //&(*head)中的&和*抵消，可以只写head
    (*head)->next = NULL;          //注意括号不能省去！
}

void insert_node_head(Link head,Link new_node)
{
    Link p = head;
    
    new_node->next = p->next;
    p->next = new_node;
}

void insert_node_tail(Link head,Link new_node)
{
    Link p = head;

    while(p->next != NULL)
    {
        p = p->next;
    }
    new_node->next = p->next;
    p->next = new_node;
}

void make_empty(Link head)
{
    Link p = head->next;

    while(head->next != NULL)
    {
        head->next = p->next;
        free(p);
        p = head->next;
    }
}

void display(Link head)
{
    Link p = head;

    printf("\n链表显示：\n");
    if(p->next == NULL)
    {
        printf("Link is empty!\n");
    }
    else
    {
        p = p->next;
        while(p != NULL)
        {
            printf("num = %d\n",p->num);
            p = p->next;
        }
    }
}

int length(Link head)
{
    Link p = head->next;
    int count = 0;

    while(p != NULL)
    {
        count++;
        p = p->next;
    }

    return count;
}

Link find(Link head,int num)
{
    Link p = head->next;

    while(p != NULL)
    {
        if(p->num == num)
        {
            return p;
        }
        p = p->next;
    }
    return p;
}

void insert_node_mid_before(Link head,Link new_node,int num)
{
    Link p = head;

    while(p->next != NULL && p->next->num != num)
    {
        p = p->next;
    }

    if(p->next == NULL)
    {
        return;
    }
    else
    {
        new_node->next = p->next;
        p->next = new_node;
    }
}

void insert_node_mid_after(Link head,Link new_node,int num)
{
    Link p = head->next;

    while(p != NULL && p->num !=num)
    {
        p = p->next;
    }

    if(p == NULL)
    {
        return;
    }
    else
    {
        new_node->next = p->next;
        p->next = new_node;
    }


}

void delete_node(Link head,int num)
{
    Link p = head;
    Link q;

    while(p->next != NULL && p ->next->num != num)
    {
        p = p->next;
    }

    if(p->next == NULL)
    {
        return;
    }
    else
    {
        q = p->next;
        p->next = p->next->next;
        free(q);
    }
}

void release_link(Link *head)
{
    Link p = *head;

    while(*head != NULL)
    {
        *head = (*head)->next;
        free(p);
        p = *head;
    }
}

int main()
{
    Link head;
    Link new_node;
    Link p;
    int i;
    int num;
    int loc;

    create_link(&head);

    for(i = 0; i < 5; i++)
    {
        create_node(&new_node);
        new_node->num = i + 1;

        //insert_node_head(head,new_node);
        insert_node_tail(head,new_node);
    }

    display(head);
    printf("链表的长度为%d\n",length(head));

    printf("\n请输入你想查找的值:");
    scanf("%d",&num);

    p = find(head,num);
    if(p == NULL)
    {
        printf("未找到你想查找的结点\n");
    }
    else
    {
        printf("你想查找的节点数值为%d\n",p->num);
    }

    printf("\n请输入你想插入的结点的数值：");
    scanf("%d",&num);
    
    create_node(&new_node);
    new_node->num = num;

    printf("请输入你想在值为哪个的结点前插入该结点:");
    scanf("%d",&num);

    insert_node_mid_before(head,new_node,num);
    display(head);
    printf("链表的长度为%d\n",length(head));


    printf("\n请输入你想插入的结点的数值：");
    scanf("%d",&num);
    
    create_node(&new_node);
    new_node->num = num;

    printf("请输入你想在值为哪个的结点后插入该结点:");
    scanf("%d",&num);

    insert_node_mid_after(head,new_node,num);
    display(head);
    printf("链表的长度为%d\n",length(head));

    printf("\n请输入你想删除的结点的值:");
    scanf("%d",&num);

    delete_node(head,num);
    display(head);
    printf("链表的长度为%d\n",length(head));

    make_empty(head);

    display(head);
    printf("链表的长度为%d\n",length(head));

    release_link(&head);
    if(head == NULL)
    {
        printf("\n释放成功\n");
    }

    return 0;
}