头插法建立单链表

#include <stdio.h>
#include <stdlib.h>
typedef struct {
	int id;
	char name[20];
}Item;

typedef struct node {
	Item data;
	struct node *next;
}Node, *List;

void initList(List *l)
{
	*l = (List)malloc(sizeof(Node));
	(*l) -> next = NULL;
}
void addFromHead(List *l, Item item)/*这里传l和l的指针效果一样*/
{
	Node *s;
	s = (Node *)malloc(sizeof(Node));
	s -> data = item;
	s -> next = (*l)->next;
	(*l)->next = s;
}

int listCount(List l)
{
	int i=0;
	while(l != NULL)
	{
		i++;
		l = l->next;
	}
	return i;
}

void reverseList(List *l)/*这里传l和l的指针效果相同*/
{
	Node *p1, *p2, *p3;
	p1 = (*l)->next;
	p2 = p1->next;
	p1->next = NULL;
	while (p2 != NULL)
	{
		p3 = p2->next;
		p2 ->next = p1;
		p1 = p2;
		p2 = p3;
	}
	(*l)->next = p1;
}

void freeList(List *l)
{
	Node * p ;
	while ((*l) != NULL)
	{
		p = (*l)->next;
		free(*l);
		(*l) = p;
	}
}
void showList(List l)
{
	while(l->next != NULL)
	{
		printf("\tList:%d,%s\n",l->next->data.id,l->next->data.name);
		l = l->next;
	}
}

int main()
{
	int i;
	List l = NULL;
	initList(&l);
	Item item[3] = {{1,"jerry"},{2,"tom"},{3,"ackerman"}};
	for (i=0; i<3; i++)
		addFromHead(&l,item[i]);
	printf("ListCount:%d\n",listCount(l));
	printf("Before reverse:\n");
	showList(l);
	reverseList(&l);
	printf("After reverse:\n");        
	showList(l);
	freeList(&l);
	return 0;
}

 输出结果：

ListCount:4
Before reverse:
	List:3,ackerman
	List:2,tom
	List:1,jerry
After reverse:
	List:1,jerry
	List:2,tom
	List:3,ackerman