why there's bug if i use static variable in recursive function ? c++

Question

what am i trying to do is write binary search tree insertion function...i know there are other ways to write this program...but i am curious about this function why doesn't it work? my code is -

void insertionbst(struct node *root,int key){  
static struct node *n = newnode(key);
if(root->data!=key){
if(root == NULL){
    root = n;
}
else if(key < root->data){
    if(root->left == NULL){
        root->left = n;
        return;
    }
    else{
    insertionbst(root->left,key);
    }
}
else{
    if(root->right == NULL){
        root->right = n;
        return;
    }
    else{
    insertionbst(root->right,key);
    }
}
}
else{
    cout<<"element already exists"<<endl;
}

}

Problem i am facing - so in this code i made static variable *n because i dont want to make copies for every recursive layer but this static variable keeps same value even if i try to insert another key for example -

insertionbst(root,30);
insertionbst(root,35);

it doesn't insert key 35 in BST instead of 35 it keeps inserting 30

Thank You for Help

Answer 1

Maybe I'm missing something, but why don't you just allocate the node when you need it?

void insertionbst(struct node *root,int key){  
    if(root->data!=key){
        if(root == NULL){
            root = newnode(key);
        }
        else if(key < root->data){
            if(root->left == NULL){
                root->left = newnode(key);
                return;
            }
            else{
                insertionbst(root->left,key);
            }
        }
        else{
            if(root->right == NULL){
                root->right = newnode(key);
                return;
            }
            else{
                insertionbst(root->right,key);
            }
        }
    }
    else{
        cout<<"element already exists"<<endl;
    }
}

I can't see any reason why you need to make copies for every recursive layer .

I think your code has bugs, it doesn't deal correctly with the situation when root equals NULL . Maybe that situation never arises in practice, in which case you still need to clean up the code.