链表的创建，删除，插入，逆序，打印

函数功能： 链表的创建 打印，插入、删除、逆序

主要出现的问题有：

1、在创建链表时，使用了:

head = NULL;

p = head;

然后让P向前走，最后得到的结果始终是head = NULL;主要原因是此时head还没有赋值，指向一个NULL，p=head之后，p指针动并不表示head也向前，因为此时两个指针并不是指向同一处的，只是他们都指向NULL而已；

正确的做法应该是：先将head->=（node*）malloc（struct student），然后将p = head；这样就不会出错，或者使用程序中所使用的方法，先将head指针指向一个实指针，然后将P指针指向head指针，这样再移动p指针时，head就会一直指向p指针的那个链表头了；

 

2 在插入链表是出现的问题和创建链表时想类似；主要思想家就是先判断要插在什么地方，然后取得前后的指针，主要注意在头和尾部的处理，头部插入时，head指针要指向新插入的那个指针；

 

3 删除链表是出现问题；始终删除不了头指针，最后发现是在main函数中出现了问题；main函数中没有用head=list_delete(head,num),子函数里的head只是作为形参传入，函数调用之后并没有改变；因此需要重新赋值；

 

4 链表的逆序主要注意的地方是：1、判断head是否为空，2、利用两个指针交替前进，3、最后在head = p 时要注意先将head->next = NULL之后再做操作head = p；

 

 

 

代码：

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

/*******************************************************************************

data: 2012.7.11

fuction :list_creat,list_del.list_invert,list_print;

****************************************************************************/

typedef struct student{
 int data;
 char name[10];
 struct student *next;
}node;

node* list_creat()
{
 node *head,*p,*s;
 int x ;
 int cycle = 1;
 head = NULL;
 while(cycle){
  printf("please input the data\n");
  scanf("%d",&x);
  if(x != 0){
          //printf("the %d's data is : %d\n", cycle, x);
   s = (node*)malloc(sizeof(struct student));
   s->data = x;
   if( head == NULL ){
    head = s;
    p = head;
   } else {
    p->next = s;
    p = s;
   }
   
   cycle++;
  }else
   break;
   //cycle = 0;
  }
 printf("the data count :%d\n",cycle);
 p->next = NULL;
 return head;
   
}

 

node *list_insert(node *head, int num)
{
 node *p, *s,*ptr;
 ptr = (node*)malloc(sizeof(struct student));
 ptr->data = num;
 p = head;
 while((ptr->data > p->data) && (p->next != NULL)){
  s = p;
  p = p->next;
  }
 if(ptr->data <= p->data){
  if (p == head){
   ptr->next = p;
   head = ptr;
   }
  else{
   s->next = ptr;
   ptr->next = p;
  }
 }
 else{
  p->next =ptr; 
  ptr->next = NULL;
 }
 return head;  
}

 

node  *list_delete(node *head, int num)
{
 node *p,*s;
 p = head;
 while((num != p->data) && (p->next != NULL)){
  s = p;
  p = p->next;
  }
 if(num == p->data){
  if(p == head)
   head = p->next;
  else
   s->next = p->next;
 }else
  printf("can not find the number %d int the list\n",num);

 return head;
   
}

 

node *list_invert(node *head)
{
 node *p,*s,*q;
 p = head;
 if(p == NULL){
  printf("the list num is NULL!\n");
  return head;
 }
 p = head;
 s = p->next;
 while(s != NULL){
  q = s->next;
  s->next = p;
  p = s;
  s = q;
 }
 head->next = NULL;
 head = p;
 return head;
 
}

int  list_print(node *head)
{
 node * p;
 int i = 1;
 p = head;
 if(p == NULL)
  printf("the list creat is err!\n");
 while(p !=  NULL){
  printf("the %d's data is : %d\n", i++, p->data);
  p = p->next;
  }
 return 0;
}

 

int main()
{
 node *head;
// head = (node*)malloc(sizeof(struct student));
 int n,m;
 int k = 1;
 while(k){
  printf("1---- creat a new list!\n ");
  printf("2---- insert a num into the new list!\n ");
  printf("3---- delete a num in the list!\n ");
  printf("4-----invert the list\n");
  printf("please input the num you want to do!\n");
  scanf("%d",&m);
  switch(m)
  {
   case 1:
    printf("--------------1 creat a new list!-----------------\n ");
    head = list_creat();
    list_print(head);
    break;
   case 2:
    printf("------------------2  insert a num into the list-----------\n");
    printf("plsease input a data :\n");
    scanf("%d",&n);
    head = list_insert(head,n);
    printf("now,print the list after insert!\n");
    list_print(head);
    break;
   case 3:
    printf("---------------3  delete a num in the list!------------------\n ");
    printf("please input the num you want to delete!\n");
    scanf("%d",&n);
    printf("----before the delete the lis is :-------\n");
    list_print(head);
    head = list_delete(head, n);
    printf("--------after the delete the lis is :--------------\n");
    list_print(head);
    break;
   case 4:
    printf("---------- 4 invert the list----------------\n");
    printf("-------before invert the list  num was------\n");
    list_print(head);
    printf("after the invert,the list was:\n");
    head = list_invert(head);
    list_print(head);
    break;
   default:
    printf("no input!\n");
    k = 0;
   break;
  }
 }
 return 0;
 
 
}