This document describes functions for a doubly linked list data structure in C including: 1) Functions for inserting nodes at the beginning, end, and at a specified position before or after a node. 2) Functions for deleting nodes from the beginning, end, and at a specified position. 3) A display function to print out the elements of the linked list. 4) Additional functions like creating new nodes, checking for invalid positions, and calculating the length.

1. Doubly Linear Linked List
/***** @author: Er. Ganesh Ram Suwal *****/
/* Doubly Linked List */
#include<stdio.h>
#include<conio.h>
#include<alloc.h>
#include<process.h>
// Global variables
int data,position,i;
//Structure for Node
struct node
{
int info;
struct node *pnext,*pprev;
};
struct node *pthis, *pnew, *ptemp, *pfirst;
// Fubction Prototype
void nifb();
void nibxp();
void niaxp();
void nife();
void ndfb();
void ndfe();
void ndfsp();
void display();
void newNode()
{
pnew = (struct node*)malloc(sizeof(struct node));
printf("Data : ");
scanf("%d",&data);
pnew->info = data;
}
void invalidPosition()
{
printf("n****************************************************n");
printf(" Invalid Position! Try Again ");
printf("n****************************************************n");
}
// Counting the nodes of Linked List
int length()
{
int count = 0;
if(pfirst == NULL)
{
return 0;
}
else
{
pthis = pfirst;
count = 1;
while(pthis->pnext != NULL)
{
pthis = pthis->pnext;

2. Doubly Linear Linked List
count = count + 1;
}
return count;
}
}
// Main program function
void main()
{
clrscr();
int choice;
start:
printf("n********* Doubly Linked List *******************n");
printf("1: Node insertion from the beginingn");
printf("2: Node insertion from the endn");
printf("3: Node insertion before Xth positionn");
printf("4: Node insertion after Xth positionn");
printf("5: Node Delete from the begining n");
printf("6: Node Delete from the endn");
printf("7: Node delete from specified positionn");
printf("8: Displayn");
printf("9: Exitn");
printf("Enter your choice :");
scanf("%d",&choice);
switch(choice)
{
case 1:nifb();
break;
case 2:nife();
break;
case 3:nibxp();
break;
case 4:niaxp();
break;
case 5:ndfb();
break;
case 6:ndfe();
break;
case 7:ndfsp();
break;
case 8:display();
break;
case 9:exit(0);
break;
default: printf("Invalid Choice");
break;
}
goto start;
}
// Node Insertion from the begining
void nifb()
{
newNode();
pnew->pprev = NULL;
if(pfirst == NULL)
{
pnew->pnext = NULL;
pfirst = pnew;

3. Doubly Linear Linked List
}
else
{
pnew->pnext = pfirst;
pfirst = pnew;
}
}
//Node insertion before Xth position
void nibxp()
{
printf("position : ");
scanf("%d",&position);
if(position > length() || position < 1)
{
invalidPosition();
}
else if(position == 1)
{
nifb();
}
else
{
newNode();
if(pfirst == NULL)
{
pnew->pnext = NULL;
pnew->pprev = NULL;
pfirst = pnew;
}
else
{
pthis = pfirst;
for(i = 0;i<position-2;i++)
{
pthis = pthis->pnext;
}
ptemp = pthis->pnext;
pthis->pnext = pnew;
pnew->pnext = ptemp;
pnew->pprev = pthis;
}
}
}
//Node Insertion after Xth Position
void niaxp()
{
printf("position : ");
scanf("%d",&position);
if(position > length() || position < 1)
{
printf("n****************************************************n");
printf("Invalid Position! Try Again ");
printf("n****************************************************n");
}
else if(position == length())
{
nife();

4. Doubly Linear Linked List
}
else
{
newNode();
if(pfirst == NULL)
{
pnew->pnext = NULL;
pnew->pprev = NULL;
pfirst = pnew;
}
else
{
pthis = pfirst;
for(i = 0;i<position-1;i++)
{
pthis = pthis->pnext;
}
ptemp = pthis->pnext;
pthis->pnext = pnew;
pnew->pnext = ptemp;
pnew->pprev = pthis;
}
}
}
// Node Insertion from the end
void nife()
{
newNode();
pnew->pnext = NULL;
if(pfirst == NULL)
{
pnew->pprev = NULL;
pfirst = pnew;
}
else
{
pthis = pfirst;
while(pthis->pnext != NULL)
{
pthis = pthis->pnext;
}
pthis->pnext = pnew;
pnew->pprev = pthis;
}
}
//node delete from the begining
void ndfb()
{
if(pfirst == NULL)
{
printf("n==================================================n");
printf(" There is no node in the list");
printf("n==================================================n");
}
else
{

5. Doubly Linear Linked List
pthis = pfirst;
if(pfirst->pnext == NULL)
{
pfirst = NULL;
}
else
{
pfirst = pthis->pnext;
pfirst->pprev = NULL;
}
printf("n=================================================================n")
;
printf("The deleted element = %d",pthis->info);
printf("n=================================================================n")
;
free(pthis);
}
}
//node delete from the end
void ndfe()
{
if(pfirst == NULL)
{
printf("n==================================================n");
printf(" There is no node in the list");
printf("n==================================================n");
}
else
{
pthis = pfirst;
if(pfirst->pnext == NULL)
{
pfirst = NULL;
printf("n=================================================================n");
printf("The deleted element = %d",pthis->info);
printf("n=================================================================n");
free(pthis);
}
else
{
while(pthis->pnext->pnext != NULL)
{
pthis = pthis->pnext;
}
printf("n=================================================================n");
printf("The deleted node = %d",pthis->pnext->info);
printf("n=================================================================n");
free(pthis->pnext);
pthis->pnext = NULL;
}
}
}

6. Doubly Linear Linked List
//node delete from the specified position
void ndfsp()
{
if(pfirst == NULL)
{
printf("n==================================================n");
printf(" There is no node in the list");
printf("n==================================================n");
}
else
{
printf("Position : ");
scanf("%d",&position);
if(position > length() || position < 1)
{
invalidPosition();
}
else if(position == 1)
{
ndfb();
}
else if(position == length())
{
ndfe();
}
else
{
pthis = pfirst;
for(i=0;i<position-2;i++)
{
pthis=pthis->pnext;
}
ptemp = pthis->pnext->pnext;
printf("n=================================================================n");
printf("The deleted element = %d",pthis->pnext->info);
printf("n=================================================================n");
free(pthis->pnext);
pthis->pnext = ptemp;
pthis->pnext->pprev = pthis;
}
}
}
//Display function
void display()
{
int l;
l = length();
printf("n=================================================================n");
if(pfirst == NULL)
{
printf("There is no data in linked List");
}
else
{
printf("Node in DLL (Length=%d) : ",l);

7. Doubly Linear Linked List
pthis = pfirst;
printf("%d ",pthis->info);
while(pthis->pnext != NULL)
{
pthis = pthis->pnext;
printf("%d ",pthis->info);
}
}
printf("n=================================================================n");
}
OUTPUT

8. Doubly Linear Linked List

9. Doubly Linear Linked List