prime in linked list & result in array

#include <bits/stdc++.h>
using namespace std;
 
// Node of the singly linked list
struct Node {
    int data;
    Node* next;
};
 
// Function to insert a node at the beginning
// of the singly Linked List
void push(Node** head_ref, int new_data)
{
    Node* new_node = new Node;
    new_node->data = new_data;
    new_node->next = (*head_ref);
    (*head_ref) = new_node;
}
 
// Function to check if a number is prime
bool isPrime(int n)
{
    // Corner cases
    if (n <= 1)
        return false;
    if (n <= 3)
        return true;
 
    // This is checked so that we can skip
    // middle five numbers in below loop
    if (n % 2 == 0 || n % 3 == 0)
        return false;
 
    for (int i = 5; i * i <= n; i = i + 6)
        if (n % i == 0 || n % (i + 2) == 0)
            return false;
 
    return true;
}
//function to print the array
void printarr(int a[], int n)
{   
    int m=sizeof(a)/sizeof(a[0]);
    for (int i = 0; i < m; i++)
        cout << a[i] << " ";
        
}
// Function to find count of prime
// nodes in a linked list
int countPrime(Node** head_ref)
{
    int count = 0;
    Node* ptr = *head_ref;
     int index=0;
    int n=5; int arr[n];
    while (ptr != NULL) {
        // If current node is prime
        if (isPrime(ptr->data)) {
            // Update count
            count++;
            arr[index++]=ptr->data;
            
        }
        ptr = ptr->next;
        
    }
    printarr(arr,index);
    return 0;
}
 
int main()
{
   
    Node* head = NULL;
 
    push(&head, 17);
    push(&head, 10);
    push(&head, 6);
    push(&head, 5);
    push(&head, 15);
 
    // Function call to print require answer
    cout << "The prime nodes in Linked List = ";
    countPrime(&head);
         
 
    return 0;
}