C++层次遍历二叉树

#include <iostream>
#define maxSize 5
using namespace std;


typedef struct BTNode
{
    char data;
    struct BTNode * lchild;
    struct BTNode * rchild;
}BTNode;

BTNode * initBTNode()
{
    BTNode *node = (BTNode*)malloc(sizeof(BTNode));
    node->lchild=0;
    node->rchild=0;
    return node;
}

BTNode * init(BTNode *p)
{
    BTNode *A=initBTNode();
    BTNode *B=initBTNode();
    BTNode *C=initBTNode();
    BTNode *D=initBTNode();
    BTNode *E=initBTNode();
    BTNode *F=initBTNode();
        
    A->data='A';
    B->data='B';
    C->data='C';
    D->data='D';
    E->data='E';
    F->data='F';
    
    C->lchild=E;
    C->rchild=F;
    B->lchild=D;
    A->rchild=C;
    A->lchild=B;

    p=A;
    return p;
}

void visit(BTNode *p)
{
    cout << p->data << " ";
}

void preorder(BTNode *p)
{
    if(p!=0)
    {
        visit(p);
        preorder(p->lchild);
        preorder(p->rchild);
    }
}

void inorder(BTNode *p)
{
    if(p!=0)
    {
        inorder(p->lchild);
        visit(p);
        inorder(p->rchild);
    }
}

void postorder(BTNode *p)
{
    if(p!=0)
    {
        postorder(p->lchild);
        postorder(p->rchild);
        visit(p);
    }
}

void level(BTNode *p)
{
    int front,rear;
    BTNode *que[maxSize];
    front = rear = 0;
    BTNode *q;
    if(p!=0)
    {
        rear=(rear+1)%maxSize;
        que[rear]=p;
        while(front!=rear)
        {
            front = (front+1)%maxSize;
            q=que[front];
            visit(q);
            if(q->lchild!=0)
            {
                rear=(rear+1)%maxSize;
                que[rear]=q->lchild;
            }
            if(q->rchild!=0)
            {
                rear=(rear+1)%maxSize;
                que[rear]=q->rchild;
            }
        }
    }
}

int main(int argc, char* argv[])
{
    BTNode *node=new BTNode;
    BTNode *p=init(node);
    cout << "先序遍历：" ;
    preorder(p);
    cout << endl;
    cout << "中序遍历：" ;
    inorder(p);
    cout << endl;
    cout << "后序遍历：" ;
    postorder(p);
    cout << endl;
    cout << "层次遍历：" ;
    level(p);
    cout << endl;
    return 0;
}