Assigning pointer to a link list node throws "Segmentation Fault" - c++

Question

I'm trying to implement insertion sort with link list in C++. But, whenever I'm trying to assign pointer to new node to a link, it gives "segmentation fault (core dumped)". I've checked the line "(*head)->next = newNode;" gives this error.
To run the program compile the program and for input copy the two lines inside comment before the start of insertionSort.
#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
class Node
{
public:
int num;
Node *prev;
Node *next;
Node(int input);
};
Node::Node(int input)
{
num = input;
prev = NULL;
next = NULL;
}
/*
5 2
1 5 3 4 2
*/
void insertionSort(Node **head, int newInput)
{
Node* newNode = new Node(newInput);
if (*head == NULL)
{
*head = newNode;
}
else
{
Node *itr = *head;
if (itr->num >= newInput)
{
newNode->next = itr->next;
itr->prev = newNode;
*head = itr;
}
else
{
Node *itr = (*head)->next;
while (itr != NULL)
{
if (itr->num >= newInput)
{
newNode->prev = itr->prev;
newNode->next = itr;
itr->prev = newNode;
newNode->prev->next = newNode;
newNode = NULL;
}
itr = itr->next;
}
if (newNode != NULL)
{
if (itr == NULL) {
(*head)->next = newNode;
}
else
itr->next = newNode;
}
}
}
}
void printList(Node *head)
{
Node *itr = head;
while (itr != NULL)
{
cout << itr->num << " ";
itr = itr->next;
}
cout << endl;
}
int main()
{
/* Enter your code here. Read input from STDIN. Print output to STDOUT */
int n, k;
cin >> n >> k;
Node *head = NULL;
int num, i = -1;
while (++i < n)
{
cin >> num;
insertionSort(&head, num);
}
printList(head);
return 0;
}

Answer 1

Try changing
itr->prev = newNode;
to
newNode->prev = newNode;

Answer 2

I'm running your code, and get a write access violation. "newNode->prev was nullptr"
You seemed got your variables mixed up in line 53:
newNode->prev->next = newNode;
should be:
its->prev->next = newNode;
And it has to be executed before its->prev is overwritten. But then the code is still not functioning as you want it. You have put some more effort into it. Within the while-loop, you set newNode to NULL and then reiterate.
And you should really comment your code. You understand your own mistakes better when you describe what you are doing.
By the way, did you notice that you mask Node* itr from line 36 at line 45? you could just reuse the existing object, as you don't use it anymore.