数据结构学习--创建链表

#include "stdio.h"
#include "stdlib.h"
struct pass
{
int number;
struct pass *next;
};

struct pass * createList(struct pass *head)
{
int i = 0;
struct pass *p1; /*要新加的节点*/
struct pass *p2; /*尾节点*/
head = NULL; /*头节点*/
p1 = (struct pass*)malloc(sizeof(struct pass));
p2 = p1;

p1->next = NULL;

for(i = 1; i<=10; ++i)
{
if(p1 == NULL)
return;
p1->number = i;
if(head == NULL)
{
head = p1; //第一次循环时, 表是空的, 将p1设置为表头,此时head == p2 == p1;
}
else
{
p2->next = p1; //第二次开始, p1是新的节点, p2是表尾, 将表尾的next指向新节点
}
p2 = p1; //p2设为表尾
p1 = (struct pass*)malloc(sizeof(struct pass));
}
p2->next = NULL; //没有这一句, p2将指向不明位置,导致下面的temp ==NULL的判断不起作用
free(p1);     //一定要将将p1 free并且置为NULL, 否则指针变成"野指针", "野指针"指程序不再使用的指针,
//程序员无法控制,free只是把指针所指的内存释放掉, 并没有删除指针.
p1 = NULL;
return head;
}

void print(struct pass *head)
{
struct pass *temp;
temp = head;
while(temp != NULL)
{
printf("%d ", temp->number);//如果没有p2->next = NULL, 将导致错误.
temp = temp->next;
}
}

int main()
{
struct pass *head = NULL;
head = createList(head);
print(head);
}