typedef struct TreeNode {    int data;    struct TreeNode *left;    struct TreeNode *right;    struct TreeNode *parent;} TreeNode;void middle_order(TreeNode *Node) {    if(Node != NULL) {        middle_order(Node->left);        printf("%d ", Node->data);        middle_order(Node->right);    }}调用时： middle_order(Root); //Root为树的根

class TreeNode{    public int data;    public TreeNode leftChild;    public TreeNode rightChild;    public static void inOrderTraversal(TreeNode node){        if(node == null){            return;        }else{            inOrderTraversal(node.leftChild);        System.out.println(node.data);        inOrderTRaversal(node.rightChild);        }    }}

/*public class BTNode                  //二叉树节点类型{    public BTNode lchild;    public BTNode rchild;    public char data;}*//*public string btstr                 //全局变数*/public string InOrder(BTNode t){    btstr="";                             InOrder1(r);    returen btstr;}public string InOrder1(BTNode t){    if(t!=null)    {        InOrder(t.lchild);        bster+=t.data.ToString()+" ";        InOrder(t.rchild);    }}

procedure mid(bt:tree);begin    if bt<>nil then begin        mid (bt^.left);        write(bt^.data);        mid (bt^.right);    end;end;