代码如下：
----------------------------------------------------------------------------
# include <stdio.h>
# include <stdlib.h>

struct node
{
    char data;
    node * next;
};

void add(node * head)
{
    printf("Now add some data to linked list\n0 for null\n");

    char oData=0;
    node * p1=NULL, *p2=NULL;
    while(scanf("%c%*c", &oData))
    {
        if (oData=='0')
            break;

        p1=(node *)malloc(sizeof(node));
        p1->data=oData;
        p1->next=NULL;

        if (head==NULL)
        {
            head=p1;
            p2=head;    //¾í2»ÄüD′Ôúò»DD￡¿
        }
        else
        {
            p2->next=p1;
            p2=p1;
        }

        printf("0 for null\n");
    }
}

void printAll(node * head)
{
    node *p1=head;

    while (p1!=NULL)
    {
        printf("%c ", p1->data);
        p1=p1->next;
    }

    printf("\n");
}

void main()
{
    node * head=NULL;
    add(head);    //add函数执行完后head仍未空指针这是为何？而如果add改为有返回值node*，然后写成这个形式 head=add(head)，此时head却不为空这是为何？
    printAll(head);
}