C二叉搜索树没有为左节点和右节点分配值？

Question

I seem to be having an issue where when I am assigning values into my binary search tree, and the root will take in the first value entered, but then after that nothing else is entered. If I go and directly take a look at root -> left or root -> right it just returns with null. I've stared at this so long I'm at my wits end. I'm sure its something really basic wrong with my recursion, but I just can't see it. I'd really appreciate any help seeing where I went wrong here.

#include <stdio.h>
#include <stdlib.h>
#include "Bst.h"


int main(int argc, char** argv) {
    int value;
    TreeNode* root = NULL;
    printf ("Enter an integer\n");
    scanf ("%d", &value);
    while (value > 0) {
        root = insert (value, root);
        printf ("Enter an integer\n");
        scanf ("%d", &value);    
    }

    printf("The inorder traversal of the tree\n");
    inOrder(root);
    printf("\n");

    printf("The preorder traversal of the tree\n");
    preOrder(root);
    printf("\n");
    return (EXIT_SUCCESS);
}



TreeNode* insert(int newValue, TreeNode* root) {
    TreeNode* temp = NULL;

    //Sets a value to the root
    if (root == NULL) {
        temp = (TreeNode*)malloc(sizeof(TreeNode));
        temp -> value = newValue;
        temp -> left = NULL;
        temp -> right = NULL;
        return temp;
    }

    //Will put a larger value to the right within the tree
    else if (newValue > (root -> value)) {
        temp = insert(newValue, (root -> right));
    }

    //Will put a smaller value to the left
    else {
        temp = insert (newValue, (root -> left));
    }
    return root;
}

void inOrder(TreeNode* root){
    if(root == NULL){
        return;
    }
    else {
        inOrder(root -> left);
        printf("%d", root -> value);
        printf(" ");
        inOrder(root -> right);
    }
    return;
}

void preOrder(TreeNode* root){
    if(root == NULL) {
        return;
    } else {
        preOrder(root -> right);
        printf("%d", root -> value);
        printf(" ");
        preOrder(root -> left);
    }
    return;
}

Answer 1

Change:

temp = insert(newValue, (root -> right));

to

root->right = insert(newValue, (root -> right));

Also change the left version the same way. Right now you are allocating the child nodes but never assigning them to the right or left pointers. They are essentially getting thrown away.

Answer 2

Pretty sure the error is that you assign the newly inserted right and left nodes to temp and not to root->right and root->left which leaves them dangling outside the tree.

Change these lines:

//Will put a larger value to the right within the tree
else if (newValue > (root -> value)){
    temp = insert(newValue, (root -> right));
}

//Will put a smaller value to the left
else{
    temp = insert (newValue, (root -> left));
}

To this:

//Will put a larger value to the right within the tree
    else if (newValue > (root -> value)) {
        root->right = insert(newValue, (root -> right));
    }

//Will put a smaller value to the left
    else {
        root->left = insert (newValue, (root -> left));
    }

This change makes your code work as expected when I tested it; both inOrder and preOrder gave correct results.

See this Ideone example