前序遍历👇

void PreOrder(BinaryTreeNode<T>* treeNode) {
		if (treeNode != NULL) {
			treeNode->VisitNode();
			PreOrder(treeNode->getLeft());
			PreOrder(treeNode->getRight());
		}
	}

中序遍历👇

void InOrder(BinaryTreeNode<T>* treeNode) {
		if (treeNode != NULL) {
			InOrder(treeNode->getLeft());
			treeNode->VisitNode();
			InOrder(treeNode->getRight());
		}
	}

后序遍历👇

void PostOrder(BinaryTreeNode<T>* treeNode) {
		if (treeNode != NULL) {
			PostOrder(treeNode->getLeft());		
			PostOrder(treeNode->getRight());
			treeNode->VisitNode();
		}
	}

完整代码👇

#include<iostream>
using namespace std;

//结点类
template<class T>
class BinaryTreeNode {
	//友元类声明
	template<class T>
	friend class BinaryTree;
private:
	T data;
	BinaryTreeNode<T>* leftchild;
	BinaryTreeNode<T>* rightchild;
public:
	//构造函数
	BinaryTreeNode() {
		leftchild = NULL;
		rightchild = NULL;
	}
	BinaryTreeNode(const T& dataValue) {
		data = dataValue;
		leftchild = NULL;
		rightchild = NULL;
	}
	BinaryTreeNode(const T& dataValue, BinaryTreeNode<T>* leftchildValue, BinaryTreeNode<T>* rightchildValue) {
		data = dataValue;
		leftchild = leftchildValue;
		rightchild = rightchildValue;
	}
	//析构函数
	~BinaryTreeNode() {
		leftchild = NULL;
		rightchild = NULL;
	}
	//访问结点
	void VisitNode() {
		cout << data << " ";
	}
	//取左结点
	BinaryTreeNode<T>* getLeft() {
		return leftchild;
	}
	//取右结点
	BinaryTreeNode<T>* getRight() {
		return rightchild;
	}
};

//二叉树类
template<class T>
class BinaryTree {
private:
	BinaryTreeNode<T>* root;
public:
	//构造函数
	BinaryTree() {
		root = NULL;
		cout << "Now start to construct the BinaryTree" << endl;
		CreateNode(root);
	}
	//析构函数
	~BinaryTree() {
		root = NULL;
	}
	//前序构建二叉树
	void CreateNode(BinaryTreeNode<T>* &treeNode) {
		cout << "Please enter a value or '#' to stop:";
		T dataValue;
		cin >> dataValue;
		treeNode = new BinaryTreeNode<T>(dataValue);
		if (treeNode->data == '#') {
			delete treeNode;
			treeNode = NULL;
		}
		else {
			CreateNode(treeNode->leftchild);
			CreateNode(treeNode->rightchild);
		}
	}
	//取根节点
	BinaryTreeNode<T>* getRoot() {
		return root;
	}
	//递归前序遍历
	void PreOrder(BinaryTreeNode<T>* treeNode) {
		if (treeNode != NULL) {
			treeNode->VisitNode();
			PreOrder(treeNode->getLeft());
			PreOrder(treeNode->getRight());
		}
	}
	//递归中序遍历
	void InOrder(BinaryTreeNode<T>* treeNode) {
		if (treeNode != NULL) {
			InOrder(treeNode->getLeft());
			treeNode->VisitNode();
			InOrder(treeNode->getRight());
		}
	}
	//递归后序遍历
	void PostOrder(BinaryTreeNode<T>* treeNode) {
		if (treeNode != NULL) {
			PostOrder(treeNode->getLeft());		
			PostOrder(treeNode->getRight());
			treeNode->VisitNode();
		}
	}
};
int main() {
	//前序构建二叉树
	BinaryTree<char> test;
	//遍历二叉树
	cout << endl << "前序遍历结果：";
	test.PreOrder(test.getRoot());
	cout << endl << "中序遍历结果：";
	test.InOrder(test.getRoot());
	cout << endl << "后序遍历结果：";
	test.PostOrder(test.getRoot());
}