vs2005下一件很奇怪的事情

#include <iostream>
using namespace std;
struct node1
{
int data;
node1* left;
node1* right;
};
node1* root=NULL;
int pre_order(node1* root)
{
if (root!=NULL)
{
cout<<root->data<<endl;
pre_order(root->left);
pre_order(root->right);
}
return 0;
}
int mid_order(node1* root)
{
if(root!=NULL)
{
mid_order(root->left);
cout<<root->data<<endl;
mid_order(root->right);
}
return 0;
}
int last_order(node1* root)
{
if (root!=NULL)
{
last_order(root->left);
last_order(root->right);
cout<<root->data<<endl;
}
return 0;
}
int main()
{
node1 node[6];
root=new node1;
root->data=0;
for (int i=0;i<6;i++)
{
node[i].data=i+1;
node[i].left=NULL;
node[i].right=NULL;
}
root->left=&node[0];
root->right=&node[1];
node[0].left=&node[2];
node[0].right=&node[3];
node[1].left=&node[4];
node[1].right=&node[5];
pre_order(root);
cout<<"this is the mid_order:  "<<endl;
mid_order(root);
cout<<"this is the last_order:  "<<endl;
last_order(root);
return 0;
}