binary search tree with void

[T4l0n]

I can't manage to make this work with a void in line 20, i can with a return struct function, but with this as soon as i call data at line 39 the program crashes.

  #include <iostream>
using namespace std;

struct Bst{
    int data;
    Bst* high;
    Bst* low;
};

Bst* root=NULL;

Bst* getnew(int num){
    Bst* temp=new Bst;
    temp->data=num;
    temp->high=NULL;
    temp->low=NULL;
    return temp;
}

void add(Bst* p,int num){
    Bst* temp=getnew(num);
    if(p==NULL){
        p=temp;
        return;
    }
    if(num<=p->data){
        add(p->low,num);
    }
    else{
        add(p->high,num);
    }
}

int main(){
    add(root,20);
    add(root,15);
    add(root,10);
    add(root,5);
    cout << root->data << "\n";
}

[Ganado]

Line 23 is only changing the local copy of the pointer address, and since you return right after that, it does nothing to your actual tree.