I can't inset a node to bin search tree - c

Question

I want to write a BST,but the insert function doesn't work. Debugging it , I found that it was not inserting.
/* Binary Search Tree (BST).demo */
#include <stdio.h>
#include <stdlib.h>
typedef struct treeNode{
int data;
struct treeNode* lChild;
struct treeNode* rChild;
} treeNode;
treeNode* createNode(){
treeNode *nNode;
nNode=(struct treeNode*)malloc(sizeof(treeNode));
nNode->data=0;
nNode->lChild=NULL;
nNode->rChild=NULL;
return nNode;
}
void insert(treeNode* rt,int idata)
{
if(rt==NULL){
treeNode* nNode;
nNode=createNode();
nNode->data=idata;
rt=nNode;
rt->lChild=NULL;
rt->rChild=NULL;
}else{
if(idata < rt->data)
insert(rt->lChild,idata);
else insert(rt->rChild,idata);
}
}
int main()
{
treeNode *root;
root=(treeNode*)malloc(sizeof(treeNode));
root->data=15;
root->lChild=NULL;
root->rChild=NULL;
insert(root,13);
if(root->lChild==NULL)
printf("root no l child\n");
// printf("root lchild data :%d",root->lChild->data);
return 0;
}

Answer 1

use this as the insert function :
void insert(treeNode** rt,int idata)
{
if((*rt)==NULL)
{
treeNode* nNode;
nNode=createNode();
nNode->data=idata;
*rt=nNode;
(*rt)->lChild=NULL;
(*rt)->rChild=NULL;
}
else
{
if(idata < (*rt)->data)
insert(&((*rt)->lChild),idata);
else
insert(&((*rt)->rChild),idata);
}
}
and the insert function call in main() as:
insert(&root,13);

Answer 2

I usually implement it like this:
void insert(treeNode* rt, int idata) {
// assert( rt != NULL );
if(idata < rt->data){
if( rt->lChild != NULL)
insert(rt->lChild, idata);
else {
rt->lChild = createNode();
rt->lChild->data = idata;
}
} else {
if( rt->rChild != NULL)
insert(rt->rChild, idata);
else {
rt->rChild = createNode();
rt->rChild->data = idata;
}
}
}
Moreover, I prefer give an argument to createNode()
treeNode* createNode(int idata){
// ...
nNode->data = idata;
// ...
}
So the insert will look like:
void insert(treeNode* rt, int idata) {
// ...
rt->lChild = createNode(idata);
// ...
rt->rChild = createNode(idata);
// ...
}