How to solve template conversion to an int - c++

Question

Well I have a task to make BST (Binary Search Tree) on a template. And I'm stuck on conversion problem, couse using template :/. I don't know how to get over it. I tried this code without template and it works normally.
#include <iostream>
using namespace std;
template <class T> struct drzewo{
private:
int value;
drzewo *l ,*r;
public:
T NewDrzewo(int key){
struct drzewo *temp=(struct drzewo*)malloc(sizeof(struct drzewo));
temp->value=key;
temp->l=temp->r=NULL;
return temp;
}
void inorder(struct drzewo *root) {
if (root != NULL) {
inorder(root->l);
cout << root->value << " -> ";
inorder(root->r);
}
}
T insert(struct drzewo *drzewo, int value) {
if (drzewo == NULL) return NewDrzewo(value);
if (value < drzewo->value){
drzewo->l=insert(drzewo->l, value);
}
else{
drzewo->r=insert(drzewo->r, value);
}
return drzewo;
}
};
int main(int argc, char** argv) {
struct drzewo <int> *root = NULL;
root->insert(root, 8);
return 0;
} ```

Answer 1

You are using the template machinery incorrectly.
template <class T> struct drzewo{
private:
int value; // THIS MAKES NO SENSE
The idea of the template is to pass thet type of the stored element as a parameter and not to hard code it. Thus you should be using
T value;
instead of
int value;
Since T is the type of your stored element and not the type of your tree,
T NewDrzewo(int key){
is also wrong, you should be using
drzewo* NewDrzewo(T key){
Likewise, T insert(... int value) should be drzewo* insert(... T value).
There are other issues unrelated to this one, for example (in no particular order):
Using malloc. Don't do that, use new instead.
Not using constructors and destructors.
Using elaborate-type-specifiers (struct drzewo) without any reason. Use drzewo instead.
Using the obsolete NULL macro. Use nullptr instead.
using namespace std is dangerous, never do that.
insert and NewDrzewo should be static functions as they do not use this. root->insert(root, 8) should be root = drzewo<int>::insert(root, 0) because root-> is illegal when root is a null pointer.