二叉树排序之从记事本中依次读取每一行通讯录内容，1.将读取的所有教师信息按照年龄构建成二叉排序树，然后，2.分别通过对二叉排序树的先序遍历显示所有教师信息，3.通过二叉排序树的后序遍历按照姓名查询某位教师通讯信息，通过二叉排序树后序遍历按照部门查询该部门所有教师的通讯信息；最后，.通过二叉排序树的中序遍历输出青年教师（≤35岁）通讯信息，遍历过程中，如果某个结点的年龄大于35岁，那么不再需要遍历该结点的右子树。主程序利用switch循环前4项功能项的源代码

以下是利用 switch 循环前 4 项功能项的源代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_NAME_LEN 20
#define MAX_DEPT_LEN 20
#define MAX_PHONE_LEN 20

struct Teacher {
    char name[MAX_NAME_LEN];
    int age;
    char dept[MAX_DEPT_LEN];
    char phone[MAX_PHONE_LEN];
    struct Teacher *left;
    struct Teacher *right;
};

typedef struct Teacher Teacher;

Teacher* create_teacher(char* name, int age, char* dept, char* phone) {
    Teacher* teacher = (Teacher*) malloc(sizeof(Teacher));
    strncpy(teacher->name, name, MAX_NAME_LEN);
    teacher->age = age;
    strncpy(teacher->dept, dept, MAX_DEPT_LEN);
    strncpy(teacher->phone, phone, MAX_PHONE_LEN);
    teacher->left = NULL;
    teacher->right = NULL;
    return teacher;
}

void insert_teacher(Teacher** root, Teacher* teacher) {
    if (*root == NULL) {
        *root = teacher;
    } else if (teacher->age < (*root)->age) {
        insert_teacher(&((*root)->left), teacher);
    } else {
        insert_teacher(&((*root)->right), teacher);
    }
}

void preorder_traversal(Teacher* root) {
    if (root == NULL) {
        return;
    }
    printf("%s %d %s %s\n", root->name, root->age, root->dept, root->phone);
    preorder_traversal(root->left);
    preorder_traversal(root->right);
}

void postorder_traversal_name(Teacher* root, char* name) {
    if (root == NULL) {
        return;
    }
    postorder_traversal_name(root->left, name);
    postorder_traversal_name(root->right, name);
    if (strcmp(root->name, name) == 0) {
        printf("%s %d %s %s\n", root->name, root->age, root->dept, root->phone);
    }
}

void postorder_traversal_dept(Teacher* root, char* dept) {
    if (root == NULL) {
        return;
    }
    postorder_traversal_dept(root->left, dept);
    postorder_traversal_dept(root->right, dept);
    if (strcmp(root->dept, dept) == 0) {
        printf("%s %d %s %s\n", root->name, root->age, root->dept, root->phone);
    }
}

void inorder_traversal_young(Teacher* root) {
    if (root == NULL) {
        return;
    }
    inorder_traversal_young(root->left);
    if (root->age <= 35) {
        printf("%s %d %s %s\n", root->name, root->age, root->dept, root->phone);
        inorder_traversal_young(root->right);
    }
}

int main() {
    Teacher* root = NULL;
    int choice;
    char name[MAX_NAME_LEN];
    int age;
    char dept[MAX_DEPT_LEN];
    char phone[MAX_PHONE_LEN];
    while (1) {
        printf("1. Insert teacher info\n");
        printf("2. Preorder traversal\n");
        printf("3. Postorder traversal by name\n");
        printf("4. Postorder traversal by dept\n");
        printf("5. Inorder traversal for young teachers\n");
        printf("6. Exit\n");
        printf("Enter your choice: ");
        scanf("%d", &choice);
        switch (choice) {
            case 1:
                printf("Enter name, age, dept and phone: ");
                scanf("%s %d %s %s", name, &age, dept, phone);
                insert_teacher(&root, create_teacher(name, age, dept, phone));
                break;
            case 2:
                printf("Teacher info (preorder traversal):\n");
                preorder_traversal(root);
                break;
            case 3:
                printf("Enter name: ");
                scanf("%s", name);
                printf("Teacher info (postorder traversal by name):\n");
                postorder_traversal_name(root, name);
                break;
            case 4:
                printf("Enter dept: ");
                scanf("%s", dept);
                printf("Teacher info (postorder traversal by dept):\n");
                postorder_traversal_dept(root, dept);
                break;
            case 5:
                printf("Young teacher info (inorder traversal):\n");
                inorder_traversal_young(root);
                break;
            case 6:
                printf("Exiting...\n");
                exit(0);
            default:
                printf("Invalid choice!\n");
        }
    }
    return 0;
}