Question

Can you make this singular linked list to doubly linked list

Create a Doubly Linked List.

Use this to create a Sorted Linked List,

Use this to create a prioritized list by use. Bring to front those links recently queried.

-----link.h------
#ifndef LINK_H
#define LINK_H

struct Link{
int data;
Link *lnkNxt;
};

#endif /* LINK_H */

----main.cpp----

//System Level Libraries
#include <iostream> //I/O Library
using namespace std; //Libraries compiled under std
#include"Link.h"
//Global Constants - Science/Math Related
//Conversions, Higher Dimensions

//Function Prototypes
void pop_front(Link *&front);
void pop_back(Link *&front);
void push_front(int data, Link *&front);
void push_back(int data, Link *&front);
void prntLst(Link *front);
void dstryLst(Link *&front);
void prntLst(Link* front);
Link *fillLnk(int); //Fill a Link
Link *fillLst(int); //Populate the List
//Execution Begins Here!

int main(int argc, char** argv) {
//Random Number Seed Set Here

//Variable Declarations
Link *lnk1;

//Variable Initialization
lnk1 = fillLst(5);

//Mapping Process Inputs to Outputs

//Display Outputs
cout << endl << "The Printed List" << endl;
prntLst(lnk1);

//Test new functions
pop_front(lnk1);
cout << endl << "The Printed List after popfront function" << endl << endl;
prntLst(lnk1);
pop_back(lnk1);
cout << endl << "The Printed List after popback function" << endl << endl;
prntLst(lnk1);
push_front(10, lnk1);
cout << endl << "The Printed List after pushfront function" << endl << endl;
prntLst(lnk1);
push_back(20, lnk1);
cout << endl << "The Printed List after pushback function" << endl << endl;
prntLst(lnk1);
//Clean Up, Delete all the elements in the list
delete (lnk1);

//Exit stage right!
return 0;
}

// function to remove the front element

void pop_front(Link *&front) {
if (front != NULL) { //if not the end of the list
Link *temp = front; // new pointer set equal to front
front = front->lnkNxt; //front points to the next node
delete(temp);
}
}

// function to remove the back element

void pop_back(Link *&front) {
if (front != NULL) {
Link *curr = front;
Link *prev = NULL;

while (curr->lnkNxt != NULL) {
prev = curr;
curr = curr->lnkNxt;
}

if (prev == NULL)
front = NULL;
else
prev->lnkNxt = curr->lnkNxt;
delete(curr);
}
}

// function to insert data at the front

void push_front(int data, Link *&front) {
Link *node = new Link;
node->data = data;
node->lnkNxt = front;
front = node;
}

// function to insert data at the end

void push_back(int data, Link *&front) {
Link *node = new Link;
node->data = data;
node->lnkNxt = NULL;

if (front == NULL)
front = node;
else {
Link *curr = front;

while (curr->lnkNxt != NULL)
curr = curr->lnkNxt;

curr->lnkNxt = node;
}
}

// function to print the list

void prntLst(Link *front) {
Link *curr = front;
while (curr != NULL) {
cout << curr->data << endl;
curr = curr->lnkNxt;
}
}

Link *fillLst(int nLinks) {
Link *front = fillLnk(1); //first Link
Link *next = front; // pointer to move thru the List
for (int i = 2; i <= nLinks; i++) {//attaches one link after another
Link *newLnk = fillLnk(i);
next->lnkNxt = newLnk;
next = newLnk;
}
next->lnkNxt = NULL;
return front;
}
//fills the list
Link *fillLnk(int data) {
Link *lnk = new Link;
lnk->data = data;
return lnk;
}

// function to destroy the list
void dstryLst(Link *&front) {
while (front != NULL) {
Link *temp = front;
front = front->lnkNxt;
delete(temp);
}
}

Answer 1

Here created function void prntLstBackward(Link* ptr) is for backward traversing in doubly linked list

Modified link.h

#ifndef LINK_H
#define LINK_H

struct Link
{
   int data;
   Link *lnkNxt;
   Link *lnkPrv;

};

#endif /* LINK_H */

Modified main.cpp

//System Level Libraries
#include <iostream.h> //I/O Library
//using namespace std; //Libraries compiled under std
#include"Link.h"
#include<stdlib.h>
//Global Constants - Science/Math Related
//Conversions, Higher Dimensions

//Function Prototypes
void pop_front(Link *&front);
void pop_back(Link *&front);
void push_front(int data, Link *&front);
void push_back(int data, Link *&front);
void prntLst(Link *front);
void dstryLst(Link *&front);
void prntLst(Link* front);
void prntLstBackward(Link* ptr);

Link *LastAddr(Link* front);
Link *fillLnk(int); //Fill a Link
Link *fillLst(int); //Populate the List
//Execution Begins Here!

int main(int argc, char** argv)
{
   //Random Number Seed Set Here

   //Variable Declarations
   Link *lnk1,*ptr;

   //Variable Initialization
   lnk1 = fillLst(5);

   //Mapping Process Inputs to Outputs

   //Display Outputs
   cout << endl << "The Printed List" << endl;
   prntLst(lnk1);
   cout <<endl<<" The list traversing from last to first"<<endl;
   ptr=LastAddr(lnk1);
   prntLstBackward(ptr);

   //Test new functions
   pop_front(lnk1);
   cout << endl << "The Printed List after popfront function" << endl << endl;
   prntLst(lnk1);
   pop_back(lnk1);
   cout << endl << "The Printed List after popback function" << endl << endl;
   prntLst(lnk1);
   push_front(10, lnk1);
   cout << endl << "The Printed List after pushfront function" << endl << endl;
   prntLst(lnk1);
   push_back(20, lnk1);
   cout << endl << "The Printed List after pushback function" << endl << endl;
   prntLst(lnk1);
   //Clean Up, Delete all the elements in the list
   delete (lnk1);

   //Exit stage right!
   return 0;
}

// function to remove the front element

void pop_front(Link *&front)
{
   if (front != NULL)
   { //if not the end of the list
       Link *temp = front; // new pointer set equal to front
       front = front->lnkNxt;
       front->lnkPrv=NULL; //front points to the next node
       delete(temp);
   }
}

// function to remove the back element

void pop_back(Link *&front)
{
   if (front != NULL)
   {
       Link *curr = front;
       Link *prev = NULL;

       while (curr->lnkNxt != NULL)
       {
           prev = curr;
           curr = curr->lnkNxt;
       }

       if (prev == NULL)
           front = NULL;
       else
       {

           prev->lnkNxt = curr->lnkNxt;
           curr->lnkNxt->lnkPrv=prev;
       }

       delete(curr);
   }
   getch();
}

// function to insert data at the front
void push_front(int data, Link *&front)
{
   Link *node = new Link;
   node->data = data;
   node->lnkNxt = front;
   node->lnkPrv=NULL;
   front = node;
}

// function to insert data at the end

void push_back(int data, Link *&front)
{
   Link *node = new Link;
   node->data = data;
   node->lnkNxt = NULL;
   node->lnkPrv=NULL;

   if (front == NULL)
       front = node;
   else
   {
       Link *curr = front;

       while (curr->lnkNxt != NULL)
           curr = curr->lnkNxt;

       curr->lnkNxt = node;
       node->lnkPrv=curr;
   }
}

// function to print the list

void prntLst(Link *front)
{
   Link *curr = front;
   while (curr != NULL)
   {
       cout << curr->data << endl;
       curr = curr->lnkNxt;
   }
}
void prntLstBackward(Link *ptr)
{
   Link *curr = ptr;
   while (curr != NULL)
   {
       cout << curr->data << endl;
       curr = curr->lnkPrv;
   }
}

Link *fillLst(int nLinks)
{
   Link *front = fillLnk(1); //first Link
   Link *next = front; // pointer to move thru the List
   for (int i = 2; i <= nLinks; i++)
   {//attaches one link after another
       Link *newLnk = fillLnk(i);
       next->lnkNxt = newLnk;
       newLnk->lnkPrv=next;
       next = newLnk;
   }
   next->lnkNxt = NULL;
   return front;
}
//fills the list
Link *fillLnk(int data)
{
   Link *lnk = new Link;
   lnk->data = data;
   lnk->lnkNxt=NULL;
   lnk->lnkPrv=NULL;
   return lnk;
}

// function to destroy the list
void dstryLst(Link *&front)
{
   while (front != NULL)
   {
       Link *temp = front;
       front = front->lnkNxt;
       delete(temp);
   }
}
Link * LastAddr(Link *front)
{
   Link *temp;
   temp=front;
   while(temp->lnkNxt!=NULL)
   temp=temp->lnkNxt;
   return temp;
}

Output