如果我执行上面的代码，并且如果有3个节点（例如1-> 2-> 3），并且插入的元素在第3个位置是10，则输出是1-> 2-> 3-> 10->向前为NULL，反向为3-> 2-> 1-> NULL。
如果我取消注释上面的代码，则该程序根本无法运行，并且在输入后出来
void insert()
{
node *newnode,*prev,*nextnode;
int i = 0,pos;
nextnode = head;
newnode = (node *)malloc(sizeof(node));
printf("Enter the postion to be inserted : \n");
scanf("%d",&pos);
printf("Enter the data : \n");
scanf("%d",&newnode->data);
// newnode->next = NULL;
// newnode->prev = NULL;
if(pos == 0)
{
newnode->next = head;
head->prev = newnode;
head = newnode;
}
else
{
while(i<pos)
{
// printf("here");
prev = nextnode;
nextnode = nextnode->next;
i++;
}
prev->next = newnode;
//newnode->prev = prev;
newnode->next = nextnode;
//nextnode->prev = newnode;
}
}
void display()
{
node *fDisp,*lDisp;
fDisp = head;
lDisp = last;
while(fDisp!= NULL)
{
printf("%d ->",fDisp->data);
fDisp = fDisp->next;
}
printf("NULL");
while(lDisp!= NULL)
{
printf("%d ->",lDisp->data);
lDisp = lDisp->prev;
}
printf("NULL");
}
答案 0 :(得分：0)
/**
* C program to insert a node in Doubly linked list
*/
#include <stdio.h>
#include <stdlib.h>
/*
* Basic structure of Node
*/
struct node {
int data;
struct node * prev;
struct node * next;
}*head, *last;
/*
* Function used in this program
*/
void createList(int n);
void displayList();
void insertAtBeginning(int data);
void insertAtEnd(int data);
void insertAtN(int data, int position);
int main()
{
int n, data, choice=1;
head = NULL;
last = NULL;
/*
* Run forever until user chooses 0
*/
while(choice != 0)
{
/*
* Menu creation to use the program
*/
printf("============================================\n");
printf("DOUBLY LINKED LIST PROGRAM\n");
printf("============================================\n");
printf("1. Create List\n");
printf("2. Insert node - at beginning\n");
printf("3. Insert node - at end\n");
printf("4. Insert node - at N\n");
printf("5. Display list\n");
printf("0. Exit\n");
printf("--------------------------------------------\n");
printf("Enter your choice : ");
scanf("%d", &choice);
/*
* Choose from different menu operation
*/
switch(choice)
{
case 1:
printf("Enter the total number of nodes in list: ");
scanf("%d", &n);
createList(n);
break;
case 2:
printf("Enter data of first node : ");
scanf("%d", &data);
insertAtBeginning(data);
break;
case 3:
printf("Enter data of last node : ");
scanf("%d", &data);
insertAtEnd(data);
break;
case 4:
printf("Enter the position where you want to insert new node: ");
scanf("%d", &n);
printf("Enter data of %d node : ", n);
scanf("%d", &data);
insertAtN(data, n);
break;
case 5:
displayList();
break;
case 0:
break;
default:
printf("Error! Invalid choice. Please choose between 0-5");
}
printf("\n\n\n\n\n");
}
return 0;
}
/**
* Creates a doubly linked list of n nodes.
* @n Number of nodes to be created
*/
void createList(int n)
{
int i, data;
struct node *newNode;
if(n >= 1)
{
/*
* Create and link the head node
*/
head = (struct node *)malloc(sizeof(struct node));
printf("Enter data of 1 node: ");
scanf("%d", &data);
head->data = data;
head->prev = NULL;
head->next = NULL;
last = head;
/*
* Create and link rest of the n-1 nodes
*/
for(i=2; i<=n; i++)
{
newNode = (struct node *)malloc(sizeof(struct node));
printf("Enter data of %d node: ", i);
scanf("%d", &data);
newNode->data = data;
newNode->prev = last; // Link new node with the previous node
newNode->next = NULL;
last->next = newNode; // Link previous node with the new node
last = newNode; // Make new node as last/previous node
}
printf("\nDOUBLY LINKED LIST CREATED SUCCESSFULLY\n");
}
}
/**
* Display content of the list from beginning to end
*/
void displayList()
{
struct node * temp;
int n = 1;
if(head == NULL)
{
printf("List is empty.\n");
}
else
{
temp = head;
printf("DATA IN THE LIST:\n");
while(temp != NULL)
{
printf("DATA of %d node = %d\n", n, temp->data);
n++;
/* Move the current pointer to next node */
temp = temp->next;
}
}
}
/**
* Inserts a new node at the beginning of the doubly linked list
* @data Data of the first node i.e. data of the new node
*/
void insertAtBeginning(int data)
{
struct node * newNode;
if(head == NULL)
{
printf("Error, List is Empty!\n");
}
else
{
newNode = (struct node *)malloc(sizeof(struct node));
newNode->data = data;
newNode->next = head; // Point to next node which is currently head
newNode->prev = NULL; // Previous node of first node is NULL
/* Link previous address field of head with newnode */
head->prev = newNode;
/* Make the new node as head node */
head = newNode;
printf("NODE INSERTED SUCCESSFULLY AT THE BEGINNING OF THE LIST\n");
}
}
/**
* Inserts a new node at the end of the doubly linked list
* @data Data of the last node i.e data of the new node
*/
void insertAtEnd(int data)
{
struct node * newNode;
if(last == NULL)
{
printf("Error, List is empty!\n");
}
else
{
newNode = (struct node *)malloc(sizeof(struct node));
newNode->data = data;
newNode->next = NULL;
newNode->prev = last;
last->next = newNode;
last = newNode;
printf("NODE INSERTED SUCCESSFULLY AT THE END OF LIST\n");
}
}
/**
* Inserts a node at any position in the doubly linked list
* @data Data of the new node to be inserted
* @position Position where to insert the new node
*/
void insertAtN(int data, int position)
{
int i;
struct node * newNode, *temp;
if(head == NULL)
{
printf("Error, List is empty!\n");
}
else
{
temp = head;
i=1;
while(i<position-1 && temp!=NULL)
{
temp = temp->next;
i++;
}
if(position == 1)
{
insertAtBeginning(data);
}
else if(temp == last)
{
insertAtEnd(data);
}
else if(temp!=NULL)
{
newNode = (struct node *)malloc(sizeof(struct node));
newNode->data = data;
newNode->next = temp->next; // Connect new node with n+1th node
newNode->prev = temp; // Connect new node with n-1th node
if(temp->next != NULL)
{
/* Connect n+1th node with new node */
temp->next->prev = newNode;
}
/* Connect n-1th node with new node */
temp->next = newNode;
printf("NODE INSERTED SUCCESSFULLY AT %d POSITION\n", position);
}
else
{
printf("Error, Invalid position\n");
}
}
}
您可以尝试使用该程序，它将向您显示所有可能的操作。