链表实现的问题。

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链表实现的问题。20

1. void Add(struct student **ps, int id, char *name, int age);
添加一个记录到链表的末尾

2. void Print(struct student *ps);
打印所有记录

3. void Del(struct student **ps, int id);
删除指定id的记录

4. int Length(struct student *ps);
得到记录的个数

5. void Search(struct student *ps, int id);
查找id匹配的记录并打印结果

6. void Insert(struct student **ps, int id, char *name, int age, int pos);
插入一个新记录
当pos=0时，插入到第一个记录的前面，以此类推
如果pos大于记录的个数，就添加到最后

7. void Empty(struct student **ps);
清空所有记录，即释放所有内存

这是需要调用的函数，附上源程序，请大家帮忙看看，谢谢。。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct student 
{
 int id;
 char name[20];
 int age;
 struct student *next;
};

void Add(struct student **ps, int id, char *name, int age);
void Print(struct student *ps);
void Del(struct student **ps, int pos);
int Length(struct student *ps);
void Search(struct student *ps, int id);
void Insert(struct student **ps, int id, char *name, int age, int pos);
void Empty(struct student **ps);


int main()
{
 struct student *head;
 
 head = NULL;


 Add(&head, 1, "a", 18);
 Add(&head, 2, "b", 19);
 Add(&head, 3, "c", 20);
 Add(&head, 4, "d", 21);

 Print(head);

 Del(&head, 2);
 
 Print(head);

 printf("Length:%d\n", Length(head));

 Search(head, 4);

 Insert(&head, 2, "B", 22, 2);Print(head);

 Empty(&head);
 
 Print(head);

 return 0;
}

void Add(struct student **ps, int id, char *name, int age) 
{
 struct student *p, *q;

 if(!ps) return;
 if(!name) return;

 p = (*ps);
 if (p)
 {
  while (p->next)
  {
   p = p->next;
  }
  p->next = (struct student*)malloc(sizeof(struct student));
  q = p->next;
 }
 else
 {
  (*ps) = (struct student*)malloc(sizeof(struct student));
  q = (*ps);
 }
 if (q)
 {
  q->id = id;
  strcpy(q->name, name);
  q->age = age;
  q->next = NULL;
 } 
 else
 {
  printf("Not enough memory!\n");
  exit(-1);
 }

}
void Print(struct student *ps)
{
 struct student *p = ps;

 printf("%10s%10s%10s\n", "id", "name", "age");
 while (p) 
 {
  printf("%10d%10s%10d\n", p->id, p->name, p->age);
  p = p->next;
 }
} 

void Del(struct student **ps, int pos)
{
 if (!ps) return;
 if (!*ps) return;
 
 struct student *p = *ps,*q = NULL; 
 while (p->next != NULL && pos != 0)
 {
  q = p;
  p = p->next;
  pos--;
 }
 if (pos)
 {
  return;
 } 
 else
 {
  q->next = p->next;
  free(p);
 }
}
int Length(struct student *ps)
{
 int nLen = 0;
 while (ps)
 {
  ps = ps->next;
  nLen++;
 }
 return nLen;
}
void Search(struct student *ps, int id)
{
 while (ps)
 {
  if (ps->id == id)
  {
   printf("id:%d\tname:%s\tage:%d\n", ps->id, ps->name, ps->age);
   break;
  }
  ps = ps->next;
 }
}
void Insert(struct student **ps, int id, char *name, int age, int pos)
{
 if (!ps) return;
 if (!*ps) return;
 
 struct student *p = *ps,*q = NULL; 
 while (p->next != NULL && pos != 0)
 {
  q = p;
  p = p->next;
  pos--;
 }
 if (pos)
 {
  return;
 } 
 else
 {
  p = (struct student *)malloc(sizeof(struct student));

  if (p)
  {
   p->id = id;
   strcpy(p->name, name);
   p->age = age;
   p->next = q->next;
   q->next = p;
  } 
  else
  {
   printf("Not enough memory!\n");
   exit(-1);
  }
 }
}
void Empty(struct student **ps)
{
 if (!ps) return;
 if (!*ps) return;
 
 if((*ps)->next)
 {
  Empty(&((*ps)->next));
 }
 free(*ps);
 (*ps) = NULL;
}