Circular Double Linked List

# include <stdio.h>
# include <stdlib.h>
# include <conio.h>
struct cdlinklist
{
struct cdlinklist *left;
int data;
struct cdlinklist *right;
};
typedef struct cdlinklist node;
node *start = NULL;
int nodectr;
node* getnode()
{
node * newnode;
newnode = (node *) malloc(sizeof(node));
printf("\n Enter data: ");
scanf("%d", &newnode -> data);
newnode -> left = NULL;
newnode -> right = NULL;
return newnode;
}
int menu()
{
int ch;
clrscr();
printf("\n 1. Create ");
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 End");
printf("\n 7. Delete a node from Middle");
printf("\n\n--------------------------");
printf("\n 8. Display the list from Left to Right");
printf("\n 9. Display the list from Right to Left");
printf("\n 10.Exit");
printf("\n\n Enter your choice: ");
scanf("%d", &ch);
return ch;
}
void cdll_createlist(int n)
{
int i;
node *newnode, *temp;
if(start == NULL)
{
nodectr = n;
for(i = 0; i < n; i++)
{
newnode = getnode();
if(start == NULL)
{
start = newnode;
newnode -> left = start;
newnode ->right = start;
}
else
{
newnode -> left = start -> left;
newnode -> right = start;
start -> left->right = newnode;
start -> left = newnode;
}
}
}
else
printf("\n List already exists..");
}
void cdll_display_left_right()
{
node *temp;
temp = start;
if(start == NULL)
printf("\n Empty List");
else
{
printf("\n The contents of List: ");
printf(" %d ", temp -> data);
temp = temp -> right;
while(temp != start)
{
printf(" %d ", temp -> data);
temp = temp -> right;
}
}
}
void cdll_display_right_left()
{
node *temp;
temp = start;
if(start == NULL)
printf("\n Empty List");
else
{
printf("\n The contents of List: ");
do
{
temp = temp -> left;
printf("\t%d", temp -> data);
} while(temp != start);
}
}
void cdll_insert_beg()
{
node *newnode;
newnode = getnode();
nodectr++;
if(start == NULL)
{
start = newnode;
newnode -> left = start;
newnode -> right = start;
}
else
{
newnode -> left = start -> left;
newnode -> right = start;
start -> left -> right = newnode;
start -> left = newnode;
start = newnode;
}
}
void cdll_insert_end()
{
node *newnode,*temp;
newnode = getnode();
nodectr++;
if(start == NULL)
{
start = newnode;
newnode -> left = start;
newnode -> right = start;
}
else
{
newnode -> left = start -> left;
newnode -> right = start;
start -> left -> right = newnode;
start -> left = newnode;
}
printf("\n Node Inserted at End");
}
void cdll_insert_mid()
{
node *newnode, *temp, *prev;
int pos, ctr = 1;
newnode = getnode();
printf("\n Enter the position: ");
scanf("%d", &pos);
if(pos - nodectr >= 2)
{
printf("\n Position is out of range..");
return;
}
if(pos > 1 && pos <= nodectr)
{
temp = start;
while(ctr < pos - 1)
{
temp = temp -> right;
ctr++;
}
newnode -> left = temp;
newnode -> right = temp -> right;
temp -> right -> left = newnode;
temp -> right = newnode;
nodectr++;
printf("\n Node Inserted at Middle.. ");
}
else
printf("position %d of list is not a middle position", pos);
}
}
void cdll_delete_beg()
{
node *temp;
if(start == NULL)
{
printf("\n No nodes exist..");
getch();
return ;
}
else
{
nodectr--;
if(nodectr == 0)
{
free(start);
start = NULL;
}
else
{
temp = start;
start = start -> right;
temp -> left -> right = start;
start -> left = temp -> left;
free(temp);
}
printf("\n Node deleted at Beginning..");
}
}
void cdll_delete_last()
{
node *temp;
if(start == NULL)
{
printf("\n No nodes exist..");
getch();
return;
}
else
{
nodectr--;
if(nodectr == 0)
{
free(start);
start = NULL;
}
else
{
temp = start;
while(temp -> right != start)
temp = temp -> right;
temp -> left -> right = temp -> right;
temp -> right -> left = temp -> left;
free(temp);
}
printf("\n Node deleted from end ");
}
}
void cdll_delete_mid()
{
int ctr = 1, pos;
node *temp;
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;
while(ctr < pos)
{
temp = temp -> right ;
ctr++;
}
temp -> right -> left = temp -> left;
temp -> left -> right = temp -> right;
free(temp);
printf("\n node deleted..");
nodectr--;
}
else
{
printf("\n It is not a middle position..");
getch();
}
}
}
void main(void)
{
int ch,n;
clrscr();
while(1)
{
ch = menu();
switch( ch)
{
case 1 :
printf("\n Enter Number of nodes to create: ");
scanf("%d", &n);
cdll_createlist(n);
printf("\n List created..");
break;
case 2 :
cdll_insert_beg();
break;
case 3 :
cdll_insert_end();
break;
case 4 :
cdll_insert_mid();
break;
case 5 :
cdll_delete_beg();
break;
case 6 :
cdll_delete_last();
break;
case 7 :
cdll_delete_mid();
break;
case 8 :
cdll_display_left_right();
break;
case 9 :
cdll_display_right_left();
break;
case 10:
exit(0);
}
getch();
}
}