Deletion of target node in doubly linked list in C++

Run

#include<iostream> 
using namespace std;

struct node {
    int num;
    struct node * preptr;
    struct node * nextptr;
}*start_node, *end_node;
 

void Listcreation(int n);
void DeleteFirstnode();
void DeleteLastnode();
void DeleteAnyNode(int pos);
void display(int a);

int main()
{
    int n,num1,a,insPlc;
    start_node = NULL;
   end_node= NULL;
         
    cout<<" Enter the number of nodes : "; cin>>n;
    Listcreation(n); 
    a=1;
    display(a);
    cout<<" Enter the position to delete a node : "; cin>>insPlc;

    
if(insPlc<1 || insPlc>n)
    {
     cout<<"\n Invalid position. Try again.\n "; } if(insPlc>=1 && insPlc<=n) { DeleteAnyNode(insPlc); a=2; display(a); } return 0; } void Listcreation(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: "; // storing 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;      // linking new nodes
                    fnNode->nextptr = NULL;        // setting the address of last node to 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 DeleteAnyNode(int pos)
{
    struct node* curNode;
    int i;

    curNode = start_node;
    for (i = 1; curNode != NULL && i < pos; i++) { curNode = curNode->nextptr;
    }

    if (pos == 1)
    {
        DeleteFirstnode();
    }
    else if (curNode == end_node)
    {
        DeleteLastnode();
    }
    else if (curNode != NULL)
    {
        curNode->preptr->nextptr = curNode->nextptr;
        curNode->nextptr->preptr = curNode->preptr;

        free(curNode); // Deleting the nth node
    }
    else
    {
        cout << "The given position is invalid!\n";
    }
}
 

void DeleteFirstnode()//deleting the first node
{
    struct node * NodeToDel;
    if(start_node == NULL)//checking if the first node is the last node or not
    {
        cout<<" Delete is not possible. No data in the list.\n"; } else { NodeToDel = start_node; start_node = start_node->nextptr;   
        start_node->preptr = NULL;     
        free(NodeToDel);           
    }
}

void DeleteLastnode()//deleting the last node
{
    struct node * NodeToDel;
 
    if(end_node== NULL)//checking whether the list has any nodes or not
    {
        cout<<" Delete is not possible. No data in the list.\n"; } else { NodeToDel = end_node; end_node= end_node->preptr;    
        end_node->nextptr = NULL;   
        free(NodeToDel);        
    }
}
void display(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; // current pointer moves to the next node
        }
    }
}