Linked storage representation of binary tree and traversal operations of preorder, inorder and postorder C language data structure (detailed notes)

The following uses C language to define a binary tree, and uses functions to achieve the following functions:
{

1. Create a binary tree containing several nodes, when the value of the input node is -1, no longer create a binary tree;
2. Realize the preorder traversal operation on the binary tree;
3. Realize the in-order traversal operation on the binary tree;
4. Implement the post-order traversal operation on the binary tree;

}

Students who are learning the data structure of c language are best not to copy it. It is the most important thing to write their own code through annotations.

Not much to say, directly on the code:

#include<stdio.h>
typedef struct tree{
    
    
	int data;//节点数据
	struct tree* rchild;//右子树
	struct tree* lchild;//左子树
}treenode;//为结构体取别名

/******创建二叉树的节点******/
treenode* createnode(int x) {
    
    
	int data,a;
	treenode* node = (treenode *)malloc(sizeof(treenode));
	scanf("%d", &data);//输入数据
	a = getchar();//吸收多余的空格
	if (data == -1)//输入-1代表节点下的子树不存数据，也就是不继续递归创建
		return NULL;
	node->data = data;//将输入的数值保存至节点
	printf("请输入%d的左子树：", data);
	node->lchild = createnode(data);//通过反复调用自身函数，达到循环子函数的目的
	printf("请输入%d的右子树：", data);
	node->rchild = createnode(data);
	return node;
}

/******前序遍历******/
void prevorder(treenode* root) {
    
    //接收主函数发来的地址
	if (root == NULL) {
    
    
		printf("#");//当前节点为空时打印#并返回
		return;
	}
	printf("[%d]", root->data);//打印当前节点
	prevorder(root->lchild);//遍历当前节点左子树
	prevorder(root->rchild);//遍历当前节点右子树
}

/******中序遍历******/
void middleorder(treenode* root) {
    
    
	if (root == NULL) {
    
    
		printf("#");
		return;
	}
	middleorder(root->lchild);//遍历左子树
	printf("[%d]", root->data);//打印当前节点
	middleorder(root->rchild);//遍历右子树
}

//后序遍历
void lastorder(treenode* root) {
    
    
	if (root == NULL) {
    
    
		printf("#");
		return;
	}
	middleorder(root->lchild);//遍历左子树
	middleorder(root->rchild);//遍历右子树
	printf("[%d]", root->data);//打印当前节点
}
int main() {
    
    
	int num;
	treenode* root= (treenode *)malloc(sizeof(treenode));
	while (1)
	{
    
    
		printf("\t提示:在输入信息后系统将自动初始化二叉树\n\n");
		printf("\t\t1.创建二叉树\n\n");
		printf("\t\t2.二叉树的前序遍历操作\n\n");
		printf("\t\t3.二叉树的中序遍历操作\n\n");
		printf("\t\t4.二叉树的后序遍历操作\n\n");
	A:	printf("*********************\n请选择功能项，并按回车执行:");
		scanf("%d", &num);
		switch (num)
		{
    
    
			/******创建二叉树******/
		case 1:
		{
    
    
			printf("请输入需要创建根节点数据(输入-1代表不创建该位置子树，为空)：");
			root=createnode(0);
			printf("\n二叉树创建完毕！\n");
			goto A;//跳转至选项菜单
		}

		/******前序遍历******/
		case 2:
		{
    
    
			printf("\n前序遍历完成(#为空子树)：");
			prevorder(root);
			printf("\n");
			goto A;
		}

		/******中序遍历******/
		case 3:
		{
    
    
			printf("\n中序遍历完成(#为空子树)：");
			middleorder(root);
			printf("\n");
			goto A;
		}

		/******后序遍历******/
		case 4:
		{
    
    
			printf("\n后序遍历完成(#为空子树)：");
			lastorder(root);
			printf("\n");
			goto A;
		}
		}
	}
}