一个函数实现树的非递归前、中、后序遍历

#include<iostream>
#define MAX 99
using namespace std;
struct BTNode {
    int data;
    BTNode *lchild, *rchild;
};
void visit(BTNode *p) {//访问
    printf("%d ", p->data);
}
void Pre_IN_Post_order(BTNode *p,int AA) {//AA=1先序 2中序 3后序
    BTNode* sta[MAX];//定义一个栈
    int top = -1;//栈顶指针
    int flag[MAX] = {};//记录第几次访问,初始化都是0
    sta[++top] = p;
    while (top!=-1) {
        p = sta[top];
        ++flag[top];
        if (flag[top] == AA) visit(p);
        switch (flag[top]) {
        case 1:
            if (p->lchild) sta[++top] = p->lchild; break;
        case 2:
            if (p->rchild) sta[++top] = p->rchild; break;
        case 3:
            flag[top--]=0;break;//为下一个可能入栈的元素进行初始化
        }
    }
}
int main() {
    int a[5] = { 1,2,3,4,5 };

    BTNode all[9];
    for (int i = 0; i < 9; ++i) {
        all[i].lchild = all[i].rchild = NULL;
        all[i].data = i;
    }
    all[0].lchild = all + 1; all[0].rchild = all + 2;
    all[1].lchild = all + 3; all[1].rchild = all + 4;
    all[2].lchild = all + 5; all[2].rchild = all + 6;
    all[4].lchild = all + 7;
    all[5].rchild = all + 8;
    Pre_IN_Post_order(all, 1); cout << endl;
    Pre_IN_Post_order(all, 2); cout << endl;
    Pre_IN_Post_order(all, 3); cout << endl;
}