Circular Single Linked List is just a single linked list in which the link field of the last node points back to the address of the first node. A circular linked list has no beginning and no end. It is necessary to establish a special pointer called start pointer always pointing to the first node of the list. Circular linked lists are frequently used instead of ordinary linked list because many operations are much easier to implement. In circular linked list no null pointers are used, hence all pointers contain valid address

The basic operations in a circular single linked list are

• Creation
• Insertion
• Deletion
• Traversing

## Source Code for Circular Single Linked List:

```# include <stdio.h>
# include <conio.h>
# include <stdlib.h>
{
int data;
};
node *start = NULL;
int nodectr;
node* getnode()
{
node * newnode;
newnode = (node *) malloc(sizeof(node));
printf("\n Enter data: ");
scanf("%d", &newnode -> data);
newnode -> next = NULL;
return newnode;
}
{
int ch;
clrscr();
printf("\n 1. Create a list ");
printf("\n\n--------------------------");
printf("\n 2. Insert a node at beginning ");
printf("\n 3. Insert a node at end");
printf("\n 4. Insert a node at middle");
printf("\n\n--------------------------");
printf("\n 5. Delete a node from beginning");
printf("\n 6. Delete a node from Last");
printf("\n 7. Delete a node from Middle");
printf("\n\n--------------------------");
printf("\n 8. Display the list");
printf("\n 9. Exit");
printf("\n\n--------------------------");
scanf("%d", &ch);
return ch;
}
void createlist(int n)
{
int i;
node *newnode;
node *temp;
nodectr = n;
for(i = 0; i < n ; i++)
{
newnode = getnode();
if(start == NULL)
{
start = newnode;
}
else
{
temp = start;
while(temp -> next != NULL)
temp = temp -> next;
temp -> next = newnode;
}
}
newnode ->next = start; /* last node is pointing to starting node */
}
void display()
{
node *temp;
temp = start;
printf("\n The contents of List (Left to Right): ");
if(start == NULL )
printf("\n Empty List");
else
{
do
{
printf("\t %d ", temp -> data);
temp = temp -> next;
} while(temp !=
start); printf(" X ");
}
}
void cll_insert_beg()
{
node *newnode, *last;
newnode = getnode();
if(start == NULL)
{
start = newnode;
newnode -> next = start;
}
else
{
last = start;
while(last -> next != start)
last = last -> next;
newnode -> next = start;
start = newnode;
last -> next = start;
}
printf("\n Node inserted at beginning..");
nodectr++;
}
void cll_insert_end()
{
node *newnode, *temp;
newnode = getnode();
if(start == NULL )
{
start = newnode;
newnode -> next = start;
}
else
{
temp = start;
while(temp -> next != start)
temp = temp -> next;
temp -> next = newnode;
newnode -> next = start;
}
printf("\n Node inserted at end..");
nodectr++;
}
void cll_insert_mid()
{
node *newnode, *temp, *prev;
int i, pos ;
newnode = getnode();
printf("\n Enter the position: ");
scanf("%d", &pos);
if(pos > 1 && pos < nodectr)
{
temp = start;
prev = temp;
i = 1;
while(i < pos)
{
prev = temp;
temp = temp -> next;
i++;
}
prev -> next = newnode;
newnode -> next = temp;
nodectr++;
printf("\n Node inserted at middle..");
}
else
{
printf("position %d of list is not a middle position ", pos);
}
}
void cll_delete_beg()
{
node *temp, *last;
if(start == NULL)
{
printf("\n No nodes exist..");
getch();
return ;
}
else
{
last = temp = start;
while(last -> next != start)
last = last -> next;
start = start -> next;
last -> next = start;
free(temp);
nodectr--;
printf("\n Node deleted..");
if(nodectr == 0)
start = NULL;
}
}
void cll_delete_last()
{
node *temp,*prev;
if(start == NULL)
{
printf("\n No nodes exist..");
getch();
return ;
}
else
{
temp = start;
prev = start;
while(temp -> next != start)
{
prev = temp;
temp = temp -> next;
}
prev -> next = start;
free(temp);
nodectr--;
if(nodectr == 0)
start = NULL;
printf("\n Node deleted..");
}
}
void cll_delete_mid()
{
int i = 0, pos;
node *temp, *prev;
if(start == NULL)
{
printf("\n No nodes exist..");
getch();
return ;
}
else
{
printf("\n Which node to delete: ");
scanf("%d", &pos);
if(pos > nodectr)
{
printf("\nThis node does not exist");
getch();
return;
}
if(pos > 1 && pos < nodectr)
{
temp=start;
prev = start;
i = 0;
while(i < pos - 1)
{
prev = temp;
temp = temp -> next ;
i++;
}
prev -> next = temp -> next;
free(temp);
nodectr--;
printf("\n Node Deleted..");
}
else
{
printf("\n It is not a middle position..");
getch();
}
}
}
void main(void)
{
int result;
int ch, n;
clrscr();
while(1)
{
switch(ch)
{
case 1 :
if(start == NULL)
{
printf("\n Enter Number of nodes to create: ");
scanf("%d", &n);
createlist(n);
printf("\nList created..");
}
else
break;
case 2 :
cll_insert_beg();
break;
case 3 :
cll_insert_end();
break;
case 4 :
cll_insert_mid();
break;
case 5 :
cll_delete_beg();
break;
case 6 :
cll_delete_last();
break;
case 7 :
cll_delete_mid();
break;
case 8 :
display();
break;
case 9 :
exit(0);
}
getch();
}
}
```