Question

Linkedlist implementation in C++

The below code I have written is almost done, I only need help to write the definition for delete_last() functio​n.
​

Language C++

// LinkedList.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <string>
#include <iostream>

using namespace std;

struct Node
{
int dataItem;//Our link list stores integers
Node *next;//this is a Node pointer that will be areference to next node in the list
};

class LinkedList
{
private:
Node *first;
public:
LinkedList();
void display();
void insert_first(int);
void insert_last(int);
int delete_first();
int delete_last();
void delete_item(int);
};

//Constructor creates an emptyt list
LinkedList::LinkedList()
{
first = NULL;

}

//Display method
void LinkedList::display()
{
Node *it = first;//This is a pointer for traversing
while (it != NULL)
{
  cout << it -> dataItem << "->";
  it = it->next;
}
cout << "null" << endl;
}

//insert_first() - inserts an item at the beginning
void LinkedList::insert_first(int x)
{
Node *temp = new Node;
temp->dataItem = x;
temp->next = first;
first = temp;
}

//insert_first() - inserts an item at the end
void LinkedList::insert_last(int x)
{
Node *temp = new Node;
temp->dataItem = x;
temp->next = NULL;
Node *ptr = first;//pointer for traversing
if (first == NULL)
{
  first = temp;
}
else
{
  while (ptr->next != NULL)
  {
   ptr = ptr->next;
  }
  ptr->next = temp;
}
}

/*Delete the first item in the list and return it.
If the list is empty, return NULL. (NULL is 0-not very
good since 0 could be in item */
int LinkedList::delete_first()
{
if (first == NULL) return NULL;

int x = first->dataItem;
first = first->next;
return x;
}

/*Delete the last item in the list and return it.
If the list is empty, return NULL. (NULL is 0-not very
good since 0 could be in item */
int LinkedList::delete_last()
{

}

/* Delete a given item from the list, if it is in the list.
   Delete the first one that is equal to the given.*/
void LinkedList::delete_item(int x)
{
//Two pointers for traversing
Node *ptr = first;
Node *pre = NULL;
while (ptr != NULL)
{
  if (ptr->dataItem == x)
  {
   break;
  }
  else
  {
   pre = ptr;
   ptr = ptr->next;
  }
   
}
if (pre == NULL)
{
  first = first->next;
}
else if (ptr != NULL)
{
  pre->next = ptr->next;
}
}

int main()
{
LinkedList myList;
cout << myList.delete_first() << endl;
//cout << myList.delete_last() << endl;
myList.insert_last(3);
myList.insert_first(5);
myList.insert_first(4);
myList.insert_first(10);
myList.insert_first(11);
myList.display();
myList.insert_last(13);
myList.display();
cout << myList.delete_first() << endl;
myList.display();
//cout << myList.delete_last() << endl;
myList.display();
myList.delete_item(31);
myList.display();
myList.delete_item(4);
myList.display();

for (;;);
return 0;
}

Answer 1

ANSWER: Here I write the delete last node funtion and it is working properly below is the code and output.

CODE:

//#include <stdafx.h>
#include <string>
#include <iostream>
using namespace std;
struct Node
{
int dataItem;//Our link list stores integers
Node *next;//this is a Node pointer that will be areference to next node in the list
};
class LinkedList
{
private:
Node *first;
public:
LinkedList();
void display();
void insert_first(int);
void insert_last(int);
int delete_first();
int delete_last();
void delete_item(int);
};
//Constructor creates an emptyt list
LinkedList::LinkedList()
{
first = NULL;
}
//Display method
void LinkedList::display()
{
Node *it = first;//This is a pointer for traversing
while (it != NULL)
{
cout << it -> dataItem << "->";
it = it->next;
}
cout << "null" << endl;
}
//insert_first() - inserts an item at the beginning
void LinkedList::insert_first(int x)
{
Node *temp = new Node;
temp->dataItem = x;
temp->next = first;
first = temp;
}
//insert_first() - inserts an item at the end
void LinkedList::insert_last(int x)
{
Node *temp = new Node;
temp->dataItem = x;
temp->next = NULL;
Node *ptr = first;//pointer for traversing
if (first == NULL)
{
first = temp;
}
else
{
while (ptr->next != NULL)
{
ptr = ptr->next;
}
ptr->next = temp;
}
}
/*Delete the first item in the list and return it.
If the list is empty, return NULL. (NULL is 0-not very
good since 0 could be in item */
int LinkedList::delete_first()
{
if (first == NULL) return NULL;
int x = first->dataItem;
first = first->next;
return x;
}
/*Delete the last item in the list and return it.
If the list is empty, return NULL. (NULL is 0-not very
good since 0 could be in item */
int LinkedList::delete_last()
{
//first check if firstNode is NULL or last node.
if(first == NULL)
return 0;
else if(first->next == NULL)
{
Node* tmp=first;
Node *temp = first;;
delete temp;
first = NULL;
return tmp->dataItem;
}
else
{
Node *one = first;
Node *two = first->next;
while(two->next != NULL){
two = two->next;
one = one->next;
}
one->next = NULL;
Node* tmp2=two;
delete two;
return tmp2->dataItem;
}
}
/* Delete a given item from the list, if it is in the list.
Delete the first one that is equal to the given.*/
void LinkedList::delete_item(int x)
{
//Two pointers for traversing
Node *ptr = first;
Node *pre = NULL;
while (ptr != NULL)
{
if (ptr->dataItem == x)
{
break;
}
else
{
pre = ptr;
ptr = ptr->next;
}

}
if (pre == NULL)
{
first = first->next;
}
else if (ptr != NULL)
{
pre->next = ptr->next;
}
}
int main()
{
LinkedList myList;
cout << myList.delete_first() << endl;
//cout << myList.delete_last() << endl;
myList.insert_last(3);
myList.insert_first(5);
myList.insert_first(4);
myList.insert_first(10);
myList.insert_first(11);
myList.display();
myList.insert_last(20);
myList.display();
cout << myList.delete_first() << endl;
myList.display();
cout << myList.delete_last() << endl;
myList.display();
myList.delete_item(31);
myList.display();
myList.delete_item(4);
myList.display();

for (;;);
return 0;
}

OUTPUT:

11-10-4->5-3-null 11-10-4->5-3-20-null 10-4->5->3->20-null 20 10-4->5->3->null 10->4->5->3->null 10-5-3->null