以下代码是我们学校提供的循环链表示例，并告诉每个学生构建自己的循环链表版本。
我的问题是，下面的代码真的是循环链表吗？
// Program of circular linked list
#include <stdio.h>
#include <malloc.h>
struct node
{
int info;
struct node *link;
}*last;
main()
{
int choice,n,m,po,i;
last=NULL;
while(1)
{
printf("1.Create List\n");
printf("2.Add at begining\n");
printf("3.Add after \n");
printf("4.Delete\n");
printf("5.Display\n");
printf("6.Quit\n");
printf("Enter your choice : ");
scanf("%d",&choice);
switch(choice)
{
case 1:
printf("How many nodes you want : ");
scanf("%d",&n);
for(i=0; i < n;i++)
{
printf("Enter the element : ");
scanf("%d",&m);
create_list(m);
}
break;
case 2:
printf("Enter the element : ");
scanf("%d",&m);
addatbeg(m);
break;
case 3:
printf("Enter the element : ");
scanf("%d",&m);
printf("Enter the position after which this element is inserted : ");
scanf("%d",&po);
addafter(m,po);
break;
case 4:
if(last == NULL)
{
printf("List underflow\n");
continue;
}
printf("Enter the number for deletion : ");
scanf("%d",&m);
del(m);
break;
case 5:
display();
break;
case 6:
exit(0);
default:
printf("Wrong choice\n");
}/*End of switch*/
}/*End of while*/
}/*End of main()*/
create_list(int num)
{
struct node *q,*tmp;
tmp= malloc(sizeof(struct node));
tmp->info = num;
if(last == NULL)
{
last = tmp;
tmp->link = last;
}
else
{
tmp->link = last->link; /*added at the end of list*/
last->link = tmp;
last = tmp;
}
}/*End of create_list()*/
addatbeg(int num)
{
struct node *tmp;
tmp = malloc(sizeof(struct node));
tmp->info = num;
tmp->link = last->link;
last->link = tmp;
}/*End of addatbeg()*/
addafter(int num,int pos)
{
struct node *tmp,*q;
int i;
q = last->link;
for(i=0; i < pos-1; i++)
{
q = q->link;
if(q == last->link)
{
printf("There are less than %d elements\n",pos);
return;
}
}/*End of for*/
tmp = malloc(sizeof(struct node) );
tmp->link = q->link;
tmp->info = num;
q->link = tmp;
if(q==last) /*Element inserted at the end*/
last=tmp;
}/*End of addafter()*/
del(int num)
{
struct node *tmp,*q;
if( last->link == last && last->info == num) /*Only one element*/
{
tmp = last;
last = NULL;
free(tmp);
return;
}
q = last->link;
if(q->info == num)
{
tmp = q;
last->link = q->link;
free(tmp);
return;
}
while(q->link != last)
{
if(q->link->info == num) /*Element deleted in between*/
{
tmp = q->link;
q->link = tmp->link;
free(tmp);
printf("%d deleted\n",num);
return;
}
q = q->link;
}/*End of while*/
if(q->link->info == num) /*Last element deleted q->link=last*/
{
tmp = q->link;
q->link = last->link;
free(tmp);
last = q;
return;
}
printf("Element %d not found\n",num);
}/*End of del()*/
display()
{
struct node *q;
if(last == NULL)
{
printf("List is empty\n");
return;
}
q = last->link;
printf("List is :\n");
while(q != last)
{
printf("%d ", q->info);
q = q->link;
}
printf("%d\n",last->info);
}/*End of display()*/
我不同意的原因是因为NULL用于检查列表中的最后一个节点。