How to add a node in Binary search tree? - data-structures

Question

struct node {
int data{};
node *right{nullptr};
node *left{nullptr};
};
class BTree {
private:
node *root;
void insert(node *sr, int num);
public:
BTree();
void buildTree(int num);
};
void BTree::insert(node *sr, int num) {
if (sr == nullptr) {
sr = new node;
sr->data = num;
} else {
if (num < sr->data)
insert(sr->left, num);
else
insert(sr->right, num);
}
}
int main() {
BTree tree;
tree.buildTree(3);
return 0;
}
I am using the above insert method to add a node to Binary Search Tree. But this method is unable to add the node , if i add a number as its root or first node the root remains nullptr.
How do i resolve this issue.

Answer 1

At the first root is nullptr , and I am sending root i.e the nullptr as the argument. As nullptr does refer to any node therefor the root is not getting updated by the operation in the method.
possible solution:
use pointer to pointer, so that address of the node can be passed and and changed.
directly acces the root to do changes.
PROTOTYPE
void insert(node **sr, int num);
BUILD TREE METHOD
void BTree::buildTree(int num) {
insert(&root, num);
}
INSERT METHOD
void BTree::insert(node **sr, int num) {
if (*sr == nullptr) {
*sr = new node;
(*sr)->data = num;
} else {
if (num < (*sr)->data)
insert(&((*sr)->left), num);
else
insert(&((*sr)->right), num);
}
}