Question

C++

I have failed to call the insert and display. I am recycling code but cannot figure out how to insert a node at the beginning and display it. Please help

#ifndef LINKEDLIST_H_INCLUDED
#define LINKEDLIST_H_INCLUDED
#include<iostream>
#include<stdlib.h>
#include<stdexcept>

using namespace std;
template <class T>
struct Node
{
T data;
Node<T> *Next, *Previous;
};

template <class T>
class Linkedlist
{
private:
Node<T> *First;
Node<T> *Last;
Node<T> *TempPrevious;
Node<T> *TempNext;
Node<T> *P;
int length;

public:

Linkedlist()
{
First = NULL;
Last = NULL;
length = 0;
}

void insertfirst(const T & data)
{
P = new Node<T>;
length++;

P->Previous = NULL;
P->data = data;
P->Next = First;
P = First;

if (length == 1)
P = Last;

if (length > 1)
{
P = P->Next;
P -> Previous = First;
}
}

void display()
{
if( length > 0)
       {
           cout << "\n\nList has " << length << " elements \n";
           P = First;

           while(P!= NULL)
              {
              if ( P->Next != NULL)
                  {
                  cout << P -> data << " at Memory Address " << P << " Pointing to " << P->Next << "\n";
}

                  else
                  {
                  cout << P -> data << " at Memory Address " << P << " Pointing to " << "Null "<< "\n";
}
P = P -> Next;
              }
          }
       else
          cout << "\nLIST is EMPTY!";

}

};

#endif // LINKEDLIST_H_INCLUDED

Answer 1

Hello i am solving your question hope this will be helpful to you and also as required by you , i have tested the code and it is now calling your insert function and also display , as you said above that your are not able to call those so i wrote code to called them in only.so i suggest you to go through the code you have written for insert and display. happy to help , kindly give a thumbs up and if you have any doubt then please do comment.

Code:-

#include<iostream>
#include<stdlib.h>
#include<stdexcept>

using namespace std;
template <class T>
struct Node
{
T data;
Node<T> *Next, *Previous;
};

template <class T>
class Linkedlist
{
private:
Node<T> *First;
Node<T> *Last;
Node<T> *TempPrevious;
Node<T> *TempNext;
Node<T> *P;
int length;

public:

Linkedlist()
{
First = NULL;
Last = NULL;
length = 0;
}

void insertfirst(const T & data)
{
P = new Node<T>;
length++;
  
P->Previous = NULL;
P->data = data;
P->Next = First;
P = First;
if (length == 1)
P = Last;
  
if (length > 1)
{
P = P->Next;
P -> Previous = First;
}
}

void display()
{
if( length > 0)
{
cout << " List has " << length << " elements ";
P = First;
while(P!= NULL)
{
if ( P->Next != NULL)
{
cout << P -> data << " at Memory Address " << P << " Pointing to " << P->Next << " ";
}
else
{
cout << P -> data << " at Memory Address " << P << " Pointing to " << "Null "<< " ";
}
P = P -> Next;
}
}
else
cout << " LIST is EMPTY!";
  
}

};

int main()
{
//Declarimng objects of different data type
Linkedlist<int> obj;
Linkedlist<float> obj1;
Linkedlist<char> obj2;
//Calling different Function of the class using object
obj.insertfirst(2);
obj.display();
obj1.insertfirst(3.3);
obj.display();
obj2.insertfirst('A');
obj.display();
return 0;
}

code image:-

output:-