BINARY SEARCH TREE creation

Question

i have written a simple code to create and insert elements into a binary search tree, when i write the code in the following manner, the chaining doesn't seem to happen, can anybody help me understand what exactly is happening in the insert function ? I know the code to insert elements into a binary search tree, just curious to know why this one doesn't work.

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

struct node {
    struct node *left;
    struct node* right;
    int element;
};

void insert(struct node *node,int x) {
    if(node==NULL) {
        node=(struct node *)malloc(sizeof(struct node));
        node->element=x;
        node->left=NULL;
        node->right=NULL;
    } else {
        if(x<node->element) {
            insert(node->left,x);}
        else {
            insert(node->right,x);
        }
    }
}

void inorder(struct node *base) {
    if(base!=NULL) {
        inorder(base->left);
        printf("%d ",base->element);
        inorder(base->right);
    }
}


int main(int argc, char *argv[]) {
    struct node *base;
    base=(struct node *)malloc(sizeof(struct node));
    base->element=1;
    base->left=NULL;
    base->right=NULL;
    insert(base,25);
    insert(base,30);
    inorder(base);

    return 0;
}

if the insert function is written this way, it works but still doesn't work for creation of the first node of the binary search tree, confused :/

void insert2(struct node *node,int x) {
    if(node==NULL) {
        node=(struct node *)malloc(sizeof(struct node));
        node->element=x;
        node->left=NULL;
        node->right=NULL;
    } else {
        if(x<node->element) {
            if(node->left==NULL) {
                node->left=(struct node *)malloc(sizeof(struct node));
                node->left->element=x;
                node->left->left=NULL;
                node->left->right=NULL;
            } else {
                insert2(node->left,x);
            }
        } else {
            if(node->right==NULL) {
                node->right=(struct node *)malloc(sizeof(struct node));
                node->right->element=x;
                node->right->left=NULL;
                node->right->right=NULL;
            } else {
                insert2(node->right,x);
            }
        }
    }
}

Answer 1

When you pass a value to a function in C, you're using pass-by-value. What that means is the value gets copied into another variable which becomes local to the function.

void change(struct node *n) {
    n = 42;
}

int main(void) {
    change(NULL); // change can't change the value of NULL, can it?
}

Now take a look at your insert function... Suppose I call insert(NULL,42);, do you think insert is trying to change NULL? Or is it trying to change some local variable, which your main function can't see?

You know what needs to be done already... Either make your insert function use an extra level of pointer indirection as you've suggested in your comments, or return the root node from insert so that you can propagate the changes made by insert into the data structure stored in main (using the assignment = operator).