Singly Linked List Infinite Loop - c++

Question

It's been a week since i started learning about linked list and i only managed to learn about singly linked list. So today i implemented the linked list which i learned in c++ and while i tried to run it the code goes into an infinite loop of some random numbers. I tried debugging the code but i coudn't find whats so ever is wrong with the code. The code is below. Help is appreciated.Thanks
#include <iostream>
using namespace std;
struct node{
int data;
node * next;
};
class singly{
private:
node * head,*tail;
public:
singly(){
head=NULL;
tail=NULL;
}
void createNode(int value){
node * temp = new node;
temp->data=value;
temp->next=NULL;
if(head==NULL){
head=temp;
tail=temp;
temp=NULL;
}
else{
tail->next=temp;
tail=temp;
}
}
void display(){
node * temp = new node;
head=temp;
while(temp!=NULL){
cout << temp->data << "\t" << endl;
temp->next=temp;
}
}
void insert_end(int value){
node*newnode = new node;
node*temp = new node;
newnode->data=value;
newnode->next=NULL;
temp=head;
while(temp->next!=NULL){
temp = temp->next;
}
temp->next=newnode;
}
void delete_node(){
node*current = new node;
node*previous = new node;
current = head;
while(current->next!=NULL){
previous=current;
current=current->next;
}
tail=previous;
previous->next=NULL;
delete current;
}
};
int main(){
singly lists;
lists.createNode(32);
lists.createNode(654);
lists.createNode(34);
lists.createNode(234);
cout<<"\n--------------------------------------------------\n";
cout<<"---------------Displaying All nodes---------------";
cout<<"\n--------------------------------------------------\n";
lists.display();
cout<<"\n--------------------------------------------------\n";
cout<<"-----------------Inserting At End-----------------";
cout<<"\n--------------------------------------------------\n";
lists.createNode(55);
lists.display();
cout<<"\n--------------------------------------------------\n";
cout<<"-----------------Deleing At End-------------------";
cout<<"\n--------------------------------------------------\n";
lists.delete_node();
lists.display();
}

Answer 1

The member function display does not make sense.
It overwtites the data member head with uninitialized newly created temp.
node * temp = new node;
head=temp;
so the function invokes undefined behavior.
The function can look like
void display()
{
for ( node * temp = head; temp != nullptr; temp = temp->next )
{
cout << temp->data << "\t";
}
}
Or it is better to define it the following way
std::ostream & display( std::ostream &os = std::cout )
{
for ( node * temp = head; temp != nullptr; temp = temp->next )
{
os << temp->data << "\t";
}
return os;
}
The data member insert_end is also wrong. It does not take into account that head and tail can be equalto nullptr and does not change them.
The function can be defined the following way
void insert_end(int value)
{
node *newnode = new node { value, nullptr };
if ( tail == nullptr )
{
head = tail = newnode;
}
else
{
tail = tail->next = newnode;
}
}
The member function delete_node firstly does not make sense for a singly-linked list and again is wrong and invokes undefined behavior. The function should remove the first node from the list.
Nevertheless if you want to remove the last node from the list then the function can look like
void delete_node()
{
if ( head != nullptr )
{
tail = nullptr;
node *current = head;
while ( current->next )
{
tail = current;
current = current->next;
}
if ( tail == nullptr )
{
head = tail;
}
else
{
tail->next = nullptr;
}
delete current;
}
}

Answer 2

For starters, display() is wrong. You want the update to be temp = temp->next; and it can also be initialized as node * temp = head hence not requiring the second line.
Your delete_node() can be re-written to:
if (head->next == NULL) // handles the case that it consists of 1 element
{
delete head;
head = NULL;
}
else
{
node *nextToEnd = head;
node *end = head->next;
while (end->next != NULL)
{
nextToEnd = end;
end = end->next;
}
delete end;
nextToEnd->next = NULL;
}
As stated in the comments, review the use of the new keyword