如下题：为什么单链表不能输出了？

[chenqin231]

#include <stdio.h>
#include <malloc.h>

typedef struct stu *list;

struct stu{

char name[10];
int age;
int class_num;
struct stu *next;
};
int main(void)
{
list st1 = NULL;
list head = NULL;
list p = NULL;
int num = 0;

for(num=0; num<3; num++)
{
st1 = (struct stu *)malloc(sizeof(struct stu));
if(head == NULL)
head = st1;

printf("请输入第%d个学生的姓名：",num+1);
scanf("%s",st1->name);
printf("请输入第%d个学生的年龄：",num+1);
scanf("%d",&st1->age);
printf("请输入第%d个学生的学号：",num+1);
scanf("%d",&st1->class_num);
st1 = st1->next;
st1 = NULL;

}
printf("学生的信息输出：\n");
for(num=0; num<3; num++)
{
printf("结果统计：第%d个学生姓名是：%s\t年龄是：%d\t 学号是：%d\n",4-num, head->name, head->age, head->class_num);
/*释放链表*/
p = head;
head = head->next;
free(p);

}

return 0;
}

[liru125504]

for(num=0; num<3; num++)
{
st1 = (struct stu *)malloc(sizeof(struct stu));
printf("请输入第%d个学生的姓名：",num+1);
scanf("%s",st1->name);
printf("请输入第%d个学生的年龄：",num+1);
scanf("%d",&st1->age);
printf("请输入第%d个学生的学号：",num+1);
scanf("%d",&st1->class_num);
if(head == NULL)
{
head = st1;
}
else
{
p->next = stl ;
}
p = stl ;
}

[pengzhixi]

你第一个循环并没有串成一个链表

[lc19881029]

尾插法：
p->next=st1;
p=st1