c++ - Segmentation fault (core dumped) while creating binary tree of given height -

this first time working trees. wrote c++ code, says segmentation fault (core dumped) , far searched, error comes accessing memory location may null. tried 'new' keyword malloc() should avoided in c++, still didn't how resolve in code.

# include<iostream> using namespace std; struct node {     int data;     node *left;     node *right; }*next;  int k=0;  void tree(int i,/*struct*/ node *next = new node) {   ++k; --i;   if (i==0)     return;   //next = new node;   next->data = k*k;   next->left = null;   next->right = null;   tree(i, next->left);   tree(i, next->right);   return ;  }   void display (node* next)  {   cout<<next->data<<" ";   if (next->left!=null)     {         display(next->left);         display(next->right);     }  }  int main()  {    int h;    cout<<"enter expected height of tree : ";    cin>>h;    node *root;    root = new node;    root->data=0;    root->left=null;    root->right=null;    tree(h, (root->left));    tree(h, (root->right));    cout<<root->data<<" ";    display(root->left);    display(root->right);    return 0;  } 

#include <iostream>  using namespace std;  struct node {     int data;     struct node *left;     struct node *right; };  void tree(int i, struct node **root, int k) {     if (i < 1)         return;      *root = new struct node;     (*root)->data = k*k;     (*root)->left = null;     (*root)->right = null;     tree(i - 1, &((*root)->left), k + 1);     tree(i - 1, &((*root)->right), k + 1); }  void display(struct node *root) {     if (root == null)         return;     cout << root->data << " ";     if (root->left != null)          display(root->left);     if (root->right != null)         display(root->right); }  int main() {     struct node *root;     int h;      cout<<"enter expected height of tree : ";     cin>>h;     tree(h, &root, 0);     display(root);     return 0; } 

i think should more read on how pointers works: http://www.tutorialspoint.com/cprogramming/c_pointers.htm

when calling tree(h, root->left) send pointers value "null" == 0x0. want allocate memory should send reference pointer. hence &root , &((*root)->left). in display function have check null values both left , right.

the code above improved , doesn't handle freeing of memory, able that, traverse tree , use delete on leafs , work root.