二叉链树遍历(递归) C++

#include <iostream>
using namespace std;
const int MAXSIZE = 100;

class BTTree
{
public:
BTTree(){
lchild = rchild = NULL;
}
int data;
BTTree * lchild;
BTTree * rchild;

void CreatBT(BTTree * &t);
void PrePrintBT(BTTree *);
void InPrintBT(BTTree *);
void PostPrintBT(BTTree *);
void LevelPrintBT(BTTree *);
};

void BTTree::CreatBT(BTTree * &t)
{

    int value;
    cin >> value;
    if(value==0){
t=NULL;
}else{
t = new BTTree;