How can I get a non-empty binary tree and print it? - c

Question

I built three files, which includes MainFunc.c, AllFun.h, and OtheFunc.c.
The program happens runtime error, which print nothing. However, I need it output a tree as previous order.
I guess the problem may be that I built an empty tree, but I can't solve it.
MainFunc.c
#include "AllFun.h"
int main(int argc, char* argv[])
{
int nums[MaxSize] = { 0 };
printf("Enter value of root node: ");
for (int i = 0; i < MaxSize; ++i) {
scanf_s("%d", &nums[i]);
}
TreeNode* root = create(nums, MaxSize);
preorder(root);
return 0;
}
AllFun.h
#include <stddef.h> // NULL
#include <stdlib.h>
#include <stdio.h>
#define MaxSize 10
typedef struct node {
int data;
struct node* lchild, * rchild;
} TreeNode;
TreeNode *create(int nums[], int n);
void preorder(TreeNode *root);
OtheFunc.c
#include "AllFun.h"
TreeNode* newNode(int v) {
TreeNode* node = (TreeNode*)malloc(sizeof(TreeNode));
if (node) {
node->data = v;
node->lchild = node->rchild = NULL;
return node;
}
}
void insert(TreeNode* root, int x)
{
if (root == NULL) {
root = newNode(x);
return;
}
if (root->data < x) {
insert(root->lchild, x);
}
else {
insert(root->rchild, x);
}
}
TreeNode *create(int nums[], int n)
{
TreeNode* root = NULL; // Build a empty root node
for (int i = 0; i < n; i++) {
insert(root, nums[i]);
}
return root;
}
void preorder(TreeNode* root)
{
if (root == NULL) {
return;
}
printf("%d ", root->data);
preorder(root->lchild);
preorder(root->rchild);
}

Answer 1

You have to pass the node as a pointer to pointer, then the function can change the pointer:
void insert(TreeNode** root, int x)
{
if (*root == NULL) {
*root = newNode(x);
return;
}
if ((*root)->data < x) {
insert(&(*root)->lchild, x);
}
else {
insert(&(*root)->rchild, x);
}
}
Call with insert(&root, nums[i]);:
https://ideone.com/nV5q1g