Deletion from Beginning in Doubly Linked List in C++

Run

#include<iostream>
#include<stdlib.h>
using namespace std;
struct node
{
  int num;
  struct node *preptr;
  struct node *nextptr;
} *start_node, *end_node;


void DlListcreation (int n);
void DeleteFirstNode ();
void displayDlList (int a);

int main ()
{
  int n, num1, a, plc;
  start_node = NULL;
  end_node = NULL;

  cout << " Enter the number of nodes: "; cin >> n;
  DlListcreation (n);
  a = 1;
  displayDlList (a);
  DeleteFirstNode ();
  a = 2;
  displayDlList (a);
  return 0;
}

void DlListcreation (int n)
{
  int i, num;
  struct node *fnNode;

  if (n >= 1)
    {
      start_node = (struct node *) malloc (sizeof (struct node));
      if (start_node != NULL)
	{
	  cout << " Enter data for node 1: "; //assigning data in the first node cin >> num;
	  start_node->num = num;
	  start_node->preptr = NULL;
	  start_node->nextptr = NULL;
	  end_node = start_node;
	  for (i = 2; i <= n; i++)
	    {
	      fnNode = (struct node *) malloc (sizeof (struct node));
	      if (fnNode != NULL)
		{
		  cout << " Enter data for node " << i << ": "; cin >> num;
		  fnNode->num = num;
		  fnNode->preptr = end_node;	// new node is linking with the previous node
		  fnNode->nextptr = NULL;	// set next address of fnnode is NULL
		  end_node->nextptr = fnNode;	// previous node is linking with the new node
		  end_node = fnNode;	// assign new node as last node
		}
	      else
		{
		  cout << " Memory can not be allocated.";
		  break;
		}
	    }
	}
      else
	{
	  cout << " Memory can not be allocated.";
	}
    }
}

void DeleteFirstNode ()
{
  struct node *NodeToDel;
  if (start_node == NULL)
    {
      cout << " Deletion is not possible. No data in the list.\n"; } else { NodeToDel = start_node; start_node = start_node->nextptr;	// move the next address of starting node to second node
      start_node->preptr = NULL;	// set previous address of staring node is NULL
      free (NodeToDel);		// delete the first node from memory
    }
}

void displayDlList (int m)
{
  struct node *tmp;
  int n = 1;
  if (start_node == NULL)
    {
      cout << " No data found in the List yet.";
    }
  else
    {
      tmp = start_node;
      if (m == 1)
	{
	  cout << "\n Data entered in the list are :\n";
	}
      else
	{
	  cout << "\n After deletion the new list are :\n";
	}
      while (tmp != NULL)
	{
	  cout << " node " << n << ": " << tmp->num << endl; n++; tmp = tmp->nextptr;
	}
    }
}