c++ - Root node in Binary search tree is null -

i learning c++ , data structures have implemented binary search tress can body tell issue in code getting root pointer null. unable create tree. final goal search key in tree. have written method it. unfortunately unable create tree. have tested writing traversal code.

#include <stdio.h> #include <conio.h> #include <iostream.h>  // node structure struct treenode {     int value;     int key;     struct treenode *left;     struct treenode *right;     treenode()     {         left=null;         right=null;     } };  void preorder (treenode *);  void insertnode(treenode *, int, int);  treenode* findnode(treenode *anode, int);  void main() {     treenode *root = null;      for(int = 15; i<= 300; i+=15) {         insertnode(root, i, i);          if (root!=null) {         cout<<root ->value<<endl;         }     }      cout<<"the preorder traversal"<<endl;     preorder(root);      getch(); }  void preorder (treenode *p) {      if (p!=null) {         cout<<p ->value<<endl;         preorder(p ->left);         preorder(p ->right);     }   else{         cout << "null"<<endl;     } }  void createnewnode(treenode *newnode, int avalue, int akey) {     newnode = new treenode; // create new node     newnode -> value = avalue; // set data     newnode -> key = akey; // set key           cout<<newnode ->value<<endl;     // set left,right     newnode -> left = newnode -> right = null; }  void insertnode(treenode *anode, int avalue, int akey) {      if (anode == null) {         treenode *newnode = new treenode; // create new node         newnode -> value = avalue; // set data         newnode -> key = akey; // set key         //createnewnode(newnode, avalue, akey);          if(newnode == null) {             cout<< "null returned"<<endl;         } else {              cout<< newnode -> key <<endl;         }         anode = newnode;      } else if (akey == anode->key) {     cout<<akey<<endl;         return;      } else if (akey < anode->key) {           insertnode((anode->left), avalue, akey);      } else {         insertnode((anode->right), avalue, akey);     } }  treenode* findnode(treenode *anode, int akey) {      if (anode == null) {         return null;     } else if (anode->key == akey) {          return anode;     } else if (akey <= anode->key) {          return findnode(anode->left, akey);     } else {          return findnode(anode->right, akey);     } } 

the main problem according me in insert node code, passing anode call value instead of call reference. instead of using treenode *anode in insert node function, try using treenode * &anode.