Question

in c++ Create a circular, doubly linked list from a file (input.txt), containing a list of names. The number of names is unknown. Prompt the user for the number of nodes to delete and then delete accordingly from the list. Assumption: The number inputted by the user will not exceed the actual number of nodes in the list.

Answer 1

Please find the solution below:

(Consider below strategy as nothing was mentioned in the question)

I have added the new node at the end of the list.

I have deleted node from the begining of the list

code.cpp

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

//structure of the node
struct node {
string data;//to store data
node *next;//to store next
node *prev;//to store prev
};

//function to delete node form list from the begin
void deleteNode(struct node *&head){
//if list is empty
if(head==NULL){
cout<<"No elements to delete.\n";
}
//if head is the only element in the list
else if(head->next==head){
cout<<head->data<<" deleted.\n";
delete head;//delete head
head = NULL; //set head to NULL
}
//if there is more then one node in the list
else{
//store the head in temp
node *temp;
temp = head;
//last node of the list
node *last;
last = head->prev;
//update last to point to head next
last->next = head->next;
//head next's prev will be last node
head->next->prev = last;

cout<<head->data<<" deleted.\n";
//head would be head->next node
head = last->next;

//delete temp node
delete temp;
}

}

//insertNode at the end.
void insertNode (string name, struct node *&head){
node * newNode;
newNode= new node;//creates new node.
newNode->data=name;//stores value.

//If the list is empty, create a single node
if(head==NULL){
newNode->next = newNode;
newNode->prev = newNode;

head = newNode;
}
// If list is not empty
else{
node *last;
//last node of the list
last = head->prev;

//next of new node is head
newNode->next = head;
//prev of head is newNode
head->prev = newNode;
//prev of new node is last
newNode->prev = last;
//next of last node is newNode
last->next = newNode;
}
}

//display th list in doubly link manner
void display(struct node* head) {
node *temp;
temp = head;

printf("\nThe List is:\n");
//traverse the list from begin
while (temp->next != head)
{
cout<<temp->data<<"<-->";
temp = temp->next;
}
//print last node data and first to make it as a doubly circular
cout<<temp->data<<"<-->"<<head->data<<"\n";
}

int main()
{
//head of the list
struct node *head=NULL;
int counter = 0;
//string to read from file
string name;
//stream for file
ifstream ifile;//to read file

//open file
ifile.open("input.txt"); //open file
   if(!ifile)
   {
       cout<<"Error in opening file..!!";
       exit(0);
   }
   //read till end of file
   while(!ifile.eof())
   {
ifile>>name; //read content form file
insertNode(name,head);//insert node into the list
counter++;
//display list after insertion
display(head);
   }
   //ask user to delete node from list
   int num;
   cout<<"Enter number of node to be deleted(will be deleted from begining of list): ";
cin>>num;

//delete num of node from list
while(num!=0){
deleteNode(head);
display(head);
num--;
}

return 0;
}

input.txt:

John
Ricky
Steve
Neil
Smith

Output:

Just to show it as a circular list, I have dispaly the head of the element again at the end