最近遭遇成都的地震，课也不上了，被余震弄得人心惶惶，每晚和朋友轮班睡觉，恼火的很。随手拿了本数据结构的书，反正闲着无聊，写了几个链表的基本程序玩玩，再熟悉熟悉链表。


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

#define LEN sizeof(struct student)
#define FORMANT() \
                  printf("==================================\n");\
                  printf("num     eng     math     avg(auto)\n");\
                  printf("==================================\n")

struct student
{
       int    num;
       float  english;
       float  math;
       float  avg;
       struct student *next;
};

int n = 0;

struct student *creat();
void prt(struct student *head);
struct student *insert(struct student *head,int index);
struct student *del(struct student *head, int index);

int main(int argc, char *argv[])
{
  struct student stu, *head;
  int pos,position;
 
  printf("创建链表：\n");
  head = creat();
  prt(head);
  printf("\n插入操作：\n");
  printf("请输入要插入的位置：");
  scanf("%d",&pos);
  head = insert(head,pos);
  prt(head);
  printf("\n删除操作：\n");
  printf("请输入要删除的位置：");
  scanf("%d",&position);
  head = del(head,position);
  prt(head);
 
  system("PAUSE");   
  return 0;
}

struct student *creat()
{
       struct student *p1, *p2, *head = NULL;
      
       p1 = p2 = (struct student *)malloc(LEN);
       printf("请输入学生的信息：\n");
       FORMANT();
       scanf("%d%f%f", &p1->num,&p1->english,&p1->math);
       p1->avg = (p1->english + p1->math)/2;
      
       while(p1->num != 0)
       {
               n++;
               if(n == 1)
               {
                    head = p1;
               }     
               else
               {
                   p2->next = p1;
               }
               p2 = p1;
               p1 = (struct student *)malloc(LEN);
               scanf("%d%f%f", &p1->num,&p1->english,&p1->math);
               p1->avg = (p1->english + p1->math)/2;
       }   
       p1->next = NULL;
       return head;
}

void prt(struct student *head)
{
     struct student *p1;
     p1 = head;
     printf("\n显示链表:\nnow there are %d datas.\n",n);
     FORMANT();
     while(p1 != NULL)
     {
           printf("%-8d%-8.2f%-9.2f%-8.2f\n", p1->num, p1->english, p1->math, p1->avg);
           p1=p1->next;
     }
}

struct student *insert(struct student *head,int index)
{
       struct student *p1, *p2 = head, *p3 = head;
      
       if(index < 1 || index > n+1)
       {
             printf("the position is overflow...\n");
             exit(1);
       }
       printf("请输入待插入的数据：\n");
       FORMANT();
      
       p1 = (struct student *)malloc(LEN);
       scanf("%d%f%f", &p1->num,&p1->english,&p1->math);
       p1->avg = (p1->english + p1->math)/2;
      
       if(index == 1)
       {
                p1->next = head;
                head = p1;
       }
       else if(index == n+1)
       {
            while(p2->next != NULL)
            {
                  p2 = p2->next;
            }
            p2->next = p1;
            p1->next = NULL;
       }
       else
       {
            int i = 1, j = 1;
            while(i < index)
            {
                  p2 = p2->next;
                  i++;
            }
            while(j < index-1)
            {
                    p3 = p3->next;
                    j++;
            }
            p3->next = p1;
            p1->next = p2;
       }
       n++;
       return head;
}

struct student *del(struct student *head, int index)
{
       struct student *p1 = head, *p2 = head, *p3 = head;
      
       if(n == 0)
       {
            printf("the list is empty!\n");
            exit(1);
       }
       if(index < 1 || index > n)
       {
                printf("the position is overflow....\n");
                exit(1);
       }
       if(index == 1)
       {
                head = p1->next;
                free(p1);
       }
       else if(index == n)
       {
            while(p1->next->next != NULL)
            {
                   p1 = p1->next;    
            }
            free(p1->next);
            p1->next = NULL;
       }
       else
       {
            int i = 1, j = 1;
            while(i < index+1)
            {
                  p2 = p2->next;
                  i++;
            }
            while(j < index-1)
            {
                    p3 = p3->next;
                    j++;
            }
            p1 = p3->next;
            p3->next = p2;
            free(p1);
       }
       n--;
       return head;
}

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