c语言 - 请帮助我，我想显示链表，反转它并显示然后再次显示它

Question

有人可以帮助我反转链表吗？ 当我选择显示时，反转列表后消失了。必须有某种方法可以打印列表的背面，该列表将保留在头部中。

#include<stdio.h>
#include<conio.h>
#include<alloc.h>
typedef struct nodes
{
    int data;
    struct node *next;
}
node;
void display(node*);
void display(node *head)
{
    while(head!=NULL)
    {
        printf("%d)->",head->data);
        head=head->next;
    }
}
void main()
{
node *head,*p,*q,*r;
int i,n,x,e,temp,a,b,c;
clrscr();
printf("nENTER NUMBER OF DATA TO BE ENTERED: ");
scanf("%d",&n);
head=(node*)malloc(sizeof(node));
printf("nENTER DATA NUMBER 1: ");
scanf("%d",&(head->data));
head->next=NULL;
p=head;
for(i=1;i<n;i++)
{
    p->next=(node*)malloc(sizeof(node));
    p=p->next;
    p->next=NULL;
    printf("ENTER DATA NUMBER %d: ",i+1);
    scanf("%d",&(p->data));
}
while(1)
{
    printf("nntttMEGA LINKED LIST PROGRAM");
    printf("n1]Display Linked List.");
    printf("n2]Delete Linked List.");
    printf("n3]Re-edit linked List.");
    printf("n4]Add Node @1st Position.");
    printf("n5]Add Node @Last Position.");
    printf("n6]Re-Create Linked List!!");
    printf("n7]Sort Linked List");
    printf("n8]Count Total Nodes.");
    printf("n9]Reverse Linked List.");
    printf("n10]EXIT!!");
    printf("nn: ");
    scanf("%d",&x);
    switch(x)
    {
    case 1:
        if(head==(0||NULL))
        {
            printf("nLIST IS EITHER EMPTY OR DELETED!!");
        }
        else
        {       printf("nYOUR LINKED LIST: ");
            p=head;
            while(p!=NULL)
            {
                printf("%d)->",p->data);
                p=p->next;
            }
        }
        break;
    case 2:
        if(head!=(NULL||0))
        {
            for(i=1;i<n;i++)
            {
                do
                {
                    p=head;
                    head=head->next;
                    free(p);
                }
                while(head->next!=NULL);
            }
            printf("nYOUR LINKED LIST HAS BEEN DELETED");
        }
        else
        {
            printf("nNO LINKED LIST AVAILABLE TO DELETE!!");
        }
        break;
    case 3:
        if(head==(NULL||0))
        {
            printf("nNOT APPLICABLE!!");
        }
        else
        {
            printf("nRE-ENTER DATA NUMBER 1: ");
            scanf("%d",&head->data);
            head->next=NULL;
            p=head;
            for(i=1;i<n;i++)
            {
                p->next=(node*)malloc(sizeof(node));
                p=p->next;
                p->next=NULL;
                printf("RE-ENTER DATA NUMBER %d: ",i+1);
                scanf("%d",&(p->data));
            }
        }
        break;
    case 4:
        if(head!=(0||NULL))
        {
            p=(node*)malloc(sizeof(node));
            printf("nENTER DATA FOR POSITION 1: ");
            scanf("%d",&(p->data));
            p->next=head;
            head=p;
            display(head);
        }
        else
        {
            printf("nNOT APPLICABLE!!");
        }
        break;
    case 5:
        if(head!=(0||NULL))
        {
            p=(node*)malloc(sizeof(node));
            printf("nENTER DATA FOR LAST POSITION: ");
            scanf("%d",&(p->data));
            p->next=NULL;
            if(head==NULL)
            display(head);
            q=head;
            while(q->next!=NULL)
            q=q->next;
            q->next=p;
            display(head);
        }
        else
        {
            printf("nNOT APPLICABLE!!");
        }
        break;
    case 6:
        if(head!=(NULL|0))
        {
            printf("nDELETE THE CURRENT LINKED LIST BEFORE CREATING A NEW ONE!!");
        }
        else
        {
            printf("nENTER NUMBER OF DATA TO BE ENTERED: ");
            scanf("%d",&n);
            head=(node*)malloc(sizeof(node));
            printf("nENTER DATA NUMBER 1: ");
            scanf("%d",&(head->data));
            head->next=NULL;
            p=head;
            for(i=1;i<n;i++)
            {
                p->next=(node*)malloc(sizeof(node));
                p=p->next;
                p->next=NULL;
                printf("ENTER DATA NUMBER %d: ",i+1);
                scanf("%d",&(p->data));
            }
        }
        break;
    case 7:
        if(head!=NULL)
        {
            printf("nBEFORE SORTING: ");
            display(head);
            q=head;
            while(q!=NULL)
            {
                p=q->next;
                while(p!=NULL)
                {
                    if((q->data)>(p->data))
                    {
                        temp=q->data;
                        q->data=p->data;
                        p->data=temp;
                    }
                    p=p->next;
                }
                q=q->next;
            }
            p=head;
            printf("nnAFTER SORTING: ");
            display(head);
        }
        else
        {
            printf("nNOT APPLICABLE!!");
        }
        break;
    case 8:
        if(head!=NULL)
        {
            p=head;
            for(temp=0;p!=NULL;temp++)
            {
                p=p->next;
            }
            printf("nTOTAL NODES: %d",temp);
        }
        else
        {
            printf("nNOT APPLICABLE!!");
        }
        break;
    case 9:
        printf("nSTILL WORKING ON THIS CODE!!");
        break;
    case 10:
        printf("nARE YOU SURE YOU WANT TO EXIT?");
        printf("nn1>Yes!tt2>NO!");
        printf("nn: ");
        scanf("%d",&e);
        if(e==1)
        {
            exit();
        }
        else
        {
            if(e==2)
            {
                break;
            }
            else
            {
                printf("nttINVALID SELECTION!!");
            }
        }
        break;
    default:
        printf("nttINVALID SELECTION!!");
        break;
    }
   }
   getch();
}

Answer 1

程序无法反转列表的原因是，当用户选择菜单选项 9 时，他们得到的只是一个声明代码尚未工作的 print 语句。

在高级别上，反转链表可以像这样完成：

for each element in the input list, from beginning to end:
    remove element from input list
    place element in the beginning of the output list
return output list