circular linked list in c

1#include <stdio.h>
2#include <string.h>
3#include <stdlib.h>
4#include <stdbool.h>
5
6struct node {
7   int data;
8   int key;
9	
10   struct node *next;
11};
12
13struct node *head = NULL;
14struct node *current = NULL;
15
16bool isEmpty() {
17   return head == NULL;
18}
19
20int length() {
21   int length = 0;
22
23   //if list is empty
24   if(head == NULL) {
25      return 0;
26   }
27
28   current = head->next;
29
30   while(current != head) {
31      length++;
32      current = current->next;   
33   }
34	
35   return length;
36}
37
38//insert link at the first location
39void insertFirst(int key, int data) {
40
41   //create a link
42   struct node *link = (struct node*) malloc(sizeof(struct node));
43   link->key = key;
44   link->data = data;
45	
46   if (isEmpty()) {
47      head = link;
48      head->next = head;
49   } else {
50      //point it to old first node
51      link->next = head;
52		
53      //point first to new first node
54      head = link;
55   }    
56}
57
58//delete first item
59struct node * deleteFirst() {
60
61   //save reference to first link
62   struct node *tempLink = head;
63	
64   if(head->next == head) {  
65      head = NULL;
66      return tempLink;
67   }     
68
69   //mark next to first link as first 
70   head = head->next;
71	
72   //return the deleted link
73   return tempLink;
74}
75
76//display the list
77void printList() {
78
79   struct node *ptr = head;
80   printf("\n[ ");
81	
82   //start from the beginning
83   if(head != NULL) {
84	
85      while(ptr->next != ptr) {     
86         printf("(%d,%d) ",ptr->key,ptr->data);
87         ptr = ptr->next;
88      }
89   }
90	
91   printf(" ]");
92}
93
94void main() {
95   insertFirst(1,10);
96   insertFirst(2,20);
97   insertFirst(3,30);
98   insertFirst(4,1);
99   insertFirst(5,40);
100   insertFirst(6,56); 
101
102   printf("Original List: "); 
103	
104   //print list
105   printList();
106
107   while(!isEmpty()) {            
108      struct node *temp = deleteFirst();
109      printf("\nDeleted value:");  
110      printf("(%d,%d) ",temp->key,temp->data);
111   }   
112	
113   printf("\nList after deleting all items: ");
114   printList();   
115}

1#include <iostream>
2using namespace std;
3
4#define  NULL  0
5
6
7struct  node
8{
9  int  data ;
10  struct  node  *next ;
11} ;
12
13struct  node  *first=NULL ;
14struct  node  *last=NULL ;
15
16void  create()
17{
18  int  i , n ;
19  struct  node  *pnode , *p ;
20
21  printf("Enter the number of nodes required:\n") ;
22  scanf("%d",&n) ;
23
24  printf("Enter the data value of each node:\n") ;
25  for(i=1 ; i<=n ; i++)
26  {
27    pnode=(struct node*)malloc(sizeof(struct node)) ;
28    if(pnode==NULL)
29    {
30      printf("Memory overflow. Unable to create.\n") ;
31      return ;
32    }
33
34    scanf("%d",&pnode->data) ;
35
36    if(first==NULL)
37	 first=last=pnode ;
38    else
39    {
40	  last->next=pnode ;
41	  last=pnode ;    /* last keeps track of last node */
42    }
43
44    last->next=first ;
45  }
46}
47
48/* This function will delete a node with value k from the Linked List if such a node exists */
49void  deletenode(int  k)
50{
51  struct  node  *p , *follow ;
52
53  /* searching the required node */
54  p=first ;
55  follow=NULL ;
56  while(follow!=last)
57  {
58    if(p->data==k)
59	  break ;
60    follow=p ;
61    p=p->next ;
62  }
63
64  if(follow==last)
65    printf("Required node not found.\n") ;
66  else
67  {
68    if(p==first&&p==last)  /* deleting the one and the only node */
69	  first=last=NULL ;
70    else if(p==first)       /* deleting the first node */
71    {
72      first=first->next ;
73      last->next=first ;
74    }
75    else if(p==last)      /* deleting the last node */
76    {
77      last=follow ;
78      last->next=first ;
79    }
80    else		/* deleting any other node */
81      follow->next=p->next ;
82
83    free(p) ;
84  }
85}
86
87/* This function will go through all the nodes of Linked List exactly once and will display data value of each node */
88void  traverse()
89{
90  struct  node  *p , *follow ;
91  if(first==NULL)
92    printf("Circularly Linked List Empty") ;
93  else
94  {
95    printf("Circularly Linked List is as shown: \n") ;
96
97    p=first ;
98    follow = NULL ;
99    while(follow!=last)
100    {
101      printf("%d " , p->data) ;
102      follow=p ;
103      p=p->next ;
104    }
105
106    printf("\n") ;
107  }
108}
109
110int main()
111{
112  int  x , k , ch ;
113 
114  do
115  {
116    printf("\n Menu: \n") ;
117    printf("1:Create Linked List \n") ;
118    printf("2:Delete Node \n") ;
119    printf("3:Traverse \n") ;
120    printf("4:Exit \n") ;
121
122    printf("\nEnter your choice: ") ;
123    scanf("%d",&ch) ;
124
125    switch(ch)
126    {
127      case 1:
128      create() ;
129      break ;
130
131      case 2:
132      printf("Enter the data value of the node to be deleted: ") ;
133      scanf("%d",&k) ;
134      deletenode(k) ;
135      break ;
136
137      case 3:
138      traverse() ;
139      break ;
140
141      case 4:
142      break ;
143    }
144 }
145 while(ch!=4) ;
146
147 return 0;
148}
149