第5章练习22

void preorder(bintree bt) {
    bintNode* st[n];
    int top = -1;
    do {
        while (bt != NULL) {
            printf("%c", bt->data);;
            top = top + 1;
            st[top] = bt;
            bt = bt->lchild;
        }
        if (top != -1) {
            bt = st[top];
            top = top - 1;
            bt = bt->rchild;
        }
    } while (top != -1 || bt != NULL);
}