Problems with binary tree

i tried to make a binary tree, but when i print it, it shows nothing.
can someone help me? here's the code:

Code:

#include<iostream>
#include<Windows.h>
#include<string>
#include<fstream>
#include<cstdarg>

using namespace std;


struct data
{
    int num;
    struct data *left, *right;
}*root = NULL;

void insert(int num, struct data *node)
{
    if(node == NULL)
    {
        node = new data;
        node->num = num;
        node->left = node->right = NULL;
    }
    else
    {
        if(num < node->num)
        {
            insert(num, node->left);
        }
        else if(num > node->num)
        {
            insert(num, node->right);
        }
    }
}

void print(struct data *node)
{
    if(node!=NULL)
    {
        print(node->left);
        cout << node->num << " ";
        print(node->right);
    }
}

int main()
{
    insert(6, root);
    insert(4, root);
    insert(7, root);
    insert(3, root);
    insert(8, root);
    print(root);
    cin.get();
    return 0;
}

1. Why make root global?

2. Since this is C++, you don't need to put "struct" in front of data all the time.

3. Your problem is that insert only modifies it's local copy of root. Use a reference to the root pointer like this:

Code:

#include<iostream>
using namespace std;

struct data {
    int num;
    data *left, *right;
};

void insert(int num, data*& node) {
    if(node == 0) {
        node = new data;
        node->num = num;
        node->left = node->right = NULL;
    }
    else
        if(num < node->num)
            insert(num, node->left);
        else if(num > node->num)
            insert(num, node->right);
}

void print(struct data *node) {
    if(node!=NULL) {
        print(node->left);
        cout << node->num << " ";
        print(node->right);
    }
}

int main() {
    data* root = 0;
    insert(6, root);
    insert(4, root);
    insert(7, root);
    insert(3, root);
    insert(8, root);
    print(root);
    return 0;
}

lol, i forget about the reference thing :P
anyway, i make my root global in case i need it later.
should it be declared on main? i tried to make it on global and it also works

Originally Posted by aquatorrent

anyway, i make my root global in case i need it later.

That is not a good reason to declare a variable global since you can always declare it when you do need it later. You should declare variables near first use.

Originally Posted by aquatorrent

should it be declared on main?

Probably.

Originally Posted by aquatorrent

i tried to make it on global and it also works

Yes, it also works. However, your program is extremely trivial. Global variables make it more difficult to reason about a larger, more complex, program.