这程序编译能通过但执行时有异常，单步执行时第二次循环有异常！
#include<stdio.h>
#include<stdlib.h>
typedef struct node
{
  char c;
  struct node *next;    
}L;
int main()
{
    L *l,*p,*q;
    char ch;
    l=(L*)malloc(sizeof(L));
    l->c='\0';//'0','/0'
    l->next=0;
    q=l;
    printf("input a charcter:\n");
    scanf("%c",&ch);
    getchar();
    while(ch!='!')
    {
        p=(L*)malloc(sizeof(L));
        p->c=ch;
        p->next=0;
        q->next=p;
        q=p;
        scanf("%c",ch);
        getchar();
        //p=0;
    }
    q=l;
    while(q->next!=0)
    {
        printf("%c",q->next->c);
        q=q->next;
    }
}