Data Structure Linked List: Reverse a Linked List in groups of given size

http://www.geeksforgeeks.org/reverse-a-list-in-groups-of-given-size/

 #include <iostream>
 #include <vector>
 #include <algorithm>
 #include <queue>
 #include <stack>
 #include <string>
 #include <fstream>
 #include <map>
 #include <set>
 using namespace std;

 struct node {
     int data;
     node *next;
     node() : data(), next(NULL) { }
     node(int d) : data(d), next(NULL) { }
 };

 void push(node* &head, int k) {
     node *new_node = new node(k);
     new_node->next = head;
     head = new_node;
 }

 node* reverselist(node *&head, int k) {
     node *cur = head;
     node *pre = NULL;
     node *next;
     int c = ;
     while (cur && c < k) {
         next = cur->next;
         cur->next = pre;
         pre = cur;
         cur = next;
         c++;
     }
     if (next) head->next = reverselist(next, k);
     return pre;
 }

 void print(node *head) {
     while (head) {
         cout << head->data << " ";
         head = head->next;
     }
 }

 int main() {
     node *head = NULL;
     push(head, );
     push(head, );
     push(head, );
     push(head, );
     push(head, );
     push(head, );
     push(head, );
     push(head, );
     head = reverselist(head, );
     print(head);
     return ;
 }