Insertion in Singly Linked List running on infinite loop - c++

Question

Linked List PrintNode function is running on an infinite loop.
class Node{
public:
int data;
Node* next;
};
Node * head; //first variable of inked list
void Insert(int x){
//insertion at beginning
Node* p = new Node;
p->data = x;
p->next = NULL; //when list is empty
//two scenarios to insert node
//one when linked list is empty
if (head == NULL){
head = p; //head becomes the first node
}
//if linked list is not empty
if (head != NULL){
p->next = head;
head = p; //pointing head at the newly created node
}
}
void PrintNode(Node* head){
for ( Node * temp = head; temp != nullptr; temp = temp->next )
{
cout << temp->data << "->";
}
}
int main (){
head = NULL; //points nowhere
int n;int x;
cin >> n;
for(int i = 0 ; i < n ;i ++){
cout << "Enter element" << endl;
cin >> x;
Insert(x);
}
PrintNode(head);
}
I expect the output to be list printed as for example: 1->2->3-> but,
running on an infinite loop.

Answer 1

The first Node you add ends up pointing at itself. Take a look at this chunk of code from Insert
if (head == NULL){
head = p; //head becomes the first node
}
//if linked list is not empty
if (head != NULL){
p->next = head;
head = p; //pointing head at the newly created node
}
You'll point head at your new Node, then enter the next if since head isn't NULL. If you replace the second if with an else, you should be fine.

Answer 2

Look carefully at this code:
if (head == NULL){
head = p; //head becomes the first node
}
//if linked list is not empty
if (head != NULL){
p->next = head;
head = p; //pointing head at the newly created node
}
When head is NULL both branches of code get run resulting in your head node pointing to itself. The correct code would be:
if (head == nullptr){
head = p; //head becomes the first node
}
//if linked list is not empty
else{
p->next = head;
head = p; //pointing head at the newly created node
}

Answer 3

When you update the head pointer as you insert your first element, both if statements will be executed and the head pointer will never be empty in the second if statement, so it should be if then else, like below
if (head == NULL){
head = p; //head becomes the first node
}
//if linked list is not empty
else if (head != NULL){
p->next = head;
head = p; //pointing head at the newly created node
}