（单链表问题）不知道为什么CreatList函数执行完head变成NULL了

#include
#include

typedef struct _node
{
    int data;
    struct _node* next;
}Node;

void CreatList(Node* head)
{
    Node* p;
    int x;
    scanf("%d",&x);
    while(x)
    {
        p = (Node*)malloc(sizeof(Node));
        p->data = x;
        p->next = head;
        head = p;
        scanf("%d",&x);
    }
}

void PrintList(Node* head)
{
    Node* current = NULL;
    current = head;
    while(current != NULL)
    {
        printf("%d",current->data);
        current = current->next;
    }
}

void FreeList(Node* head)
{
    Node* current = head;
    while(current != NULL)
    {
        head = current->next;
        free(current);
        current = head;
    }
}

int main()
{
    struct _node* head = NULL;
    CreatList(head);

    PrintList(head);
    FreeList(head);
    return 0;
}

因为函数中是不能实现指针参数自身地址的修改的
修改为：

 
#include<stdio.h>
#include<stdlib.h>
typedef struct _node
{
    int data;
    struct _node* next;
}Node;
Node* CreatList( )
{
    Node* p,*head = NULL;
    int x;
    scanf("%d",&x);
    while(x)
    {
        p = (Node*)malloc(sizeof(Node));
        p->data = x;
        p->next = head;
        head = p;
        scanf("%d",&x);
    }
    return head;
}
void PrintList(Node* head)
{
    Node* current = NULL;
    current = head;
    while(current != NULL)
    {
        printf("%d",current->data);
        current = current->next;
    }
}
void FreeList(Node* head)
{
    Node* current = head;
    while(current != NULL)
    {
        head = current->next;
        free(current);
        current = head;
    }
}
int main()
{
    Node* head = CreatList();
    PrintList(head);
    FreeList(head);
    return 0;
}

指针作为参数，在函数中修改这个指针的指向，需要传递这个指针的地址。

void CreatList(Node** head)，
*head = p;

CreatList(&head);