diff --git a/README.md b/README.md
deleted file mode 100644
index c0cc583..0000000
--- a/README.md
+++ /dev/null
@@ -1,2 +0,0 @@
-# smarthomework
-
diff --git a/doc/README.md b/doc/README.md
new file mode 100644
index 0000000..da4ee2d
--- /dev/null
+++ b/doc/README.md
@@ -0,0 +1,22 @@
+# 中小学数学卷子自动生成程序
+
+## 功能概览
+- 账户登录：支持小学、初中、高中各三位教师账号，登录成功提示当前难度。
+- 出题控制：支持输入 10-30 道题的数量限制，-1 退出当前登录。
+- 题目生成：根据难度生成符合运算规则的题目，并保证不与历史题库重复。
+- 难度切换：输入 `切换为小学|初中|高中` 可即时切换出题类型。
+- 结果保存：按 `YYYY-MM-DD-HH-mm-ss.txt` 格式保存在 `generated_questions/<用户名>/` 目录下，题号与空行符合要求。
+
+## 使用方式
+1. 在项目根目录执行 `javac $(find src -name '*.java') -d out` 完成编译。
+2. 执行 `java -cp out com.personalproject.MathExamApplication` 启动程序。
+3. 根据提示输入用户名、密码（以空格分隔）。
+4. 输入题目数量或切换命令生成试题，生成完成后可继续出题或输入 `-1` 退出当前账号。
+5. 登录新账号或结束程序（直接回车结束输入即可退出）。
+
+## 目录结构
+```
+src/                    Java 源码（遵循 Google Java Style）
+doc/README.md           项目说明文档
+generated_questions/    程序运行后生成的题目文件夹
+```
diff --git a/src/com/personalproject/MathExamApplication.java b/src/com/personalproject/MathExamApplication.java
new file mode 100644
index 0000000..498143a
--- /dev/null
+++ b/src/com/personalproject/MathExamApplication.java
@@ -0,0 +1,172 @@
+package com.personalproject;
+
+import com.personalproject.auth.AccountRepository;
+import com.personalproject.auth.UserAccount;
+import com.personalproject.generator.HighSchoolQuestionGenerator;
+import com.personalproject.generator.MiddleSchoolQuestionGenerator;
+import com.personalproject.generator.PrimaryQuestionGenerator;
+import com.personalproject.generator.QuestionGenerator;
+import com.personalproject.model.DifficultyLevel;
+import com.personalproject.service.QuestionGenerationService;
+import com.personalproject.storage.QuestionStorageService;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Path;
+import java.util.EnumMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Scanner;
+import java.util.Set;
+
+/**
+ * 数学试卷自动生成命令行程序的入口。
+ */
+public final class MathExamApplication {
+  private final AccountRepository accountRepository = new AccountRepository();
+  private final QuestionGenerationService questionGenerationService;
+  private final QuestionStorageService questionStorageService = new QuestionStorageService();
+
+  public MathExamApplication() {
+    Map<DifficultyLevel, QuestionGenerator> generatorMap = new EnumMap<>(DifficultyLevel.class);
+    generatorMap.put(DifficultyLevel.PRIMARY, new PrimaryQuestionGenerator());
+    generatorMap.put(DifficultyLevel.MIDDLE, new MiddleSchoolQuestionGenerator());
+    generatorMap.put(DifficultyLevel.HIGH, new HighSchoolQuestionGenerator());
+    questionGenerationService = new QuestionGenerationService(generatorMap);
+  }
+
+  public static void main(String[] args) {
+    MathExamApplication application = new MathExamApplication();
+    application.run();
+  }
+
+  private void run() {
+    Scanner scanner = new Scanner(System.in, StandardCharsets.UTF_8);
+    while (true) {
+      UserAccount account = promptLogin(scanner);
+      if (account == null) {
+        return;
+      }
+      handleSession(scanner, account);
+    }
+  }
+
+  private UserAccount promptLogin(Scanner scanner) {
+    while (true) {
+      System.out.print("请输入用户名和密码（以空格分隔）：");
+      if (!scanner.hasNextLine()) {
+        return null;
+      }
+      String input = scanner.nextLine().trim();
+      if (input.isEmpty()) {
+        continue;
+      }
+      String[] parts = input.split("\\s+");
+      if (parts.length != 2) {
+        System.out.println("请输入正确的用户名、密码");
+        continue;
+      }
+      Optional<UserAccount> account = accountRepository.authenticate(parts[0], parts[1]);
+      if (account.isPresent()) {
+        DifficultyLevel level = account.get().difficultyLevel();
+        System.out.println("当前选择为" + level.getDisplayName() + "出题");
+        return account.get();
+      }
+      System.out.println("请输入正确的用户名、密码");
+    }
+  }
+
+  private void handleSession(Scanner scanner, UserAccount account) {
+    DifficultyLevel currentLevel = account.difficultyLevel();
+    Set<String> existingQuestions = loadExistingQuestions(account.username());
+    while (true) {
+      System.out.print(
+          "准备生成"
+              + currentLevel.getDisplayName()
+              + "数学题目，请输入生成题目数量（输入-1将退出当前用户，重新登录）：");
+      if (!scanner.hasNextLine()) {
+        return;
+      }
+      String input = scanner.nextLine().trim();
+      if (input.isEmpty()) {
+        continue;
+      }
+      if (input.startsWith("切换为")) {
+        currentLevel = processSwitchCommand(input, currentLevel);
+        continue;
+      }
+      if ("-1".equals(input)) {
+        System.out.println("已退出当前用户。");
+        return;
+      }
+      Integer questionCount = parseQuestionCount(input);
+      if (questionCount == null) {
+        continue;
+      }
+      generateAndPersistQuestions(account, currentLevel, questionCount, existingQuestions);
+    }
+  }
+
+  private DifficultyLevel processSwitchCommand(String input, DifficultyLevel currentLevel) {
+    String targetName = input.substring("切换为".length()).trim();
+    Optional<DifficultyLevel> targetLevel = DifficultyLevel.fromDisplayName(targetName);
+    if (targetLevel.isEmpty()) {
+      System.out.println("请输入小学、初中和高中三个选项中的一个");
+      return currentLevel;
+    }
+    DifficultyLevel level = targetLevel.get();
+    System.out.println(
+        "系统提示: 准备生成"
+            + level.getDisplayName()
+            + "数学题目，请输入生成题目数量（输入-1将退出当前用户，重新登录）：");
+    return level;
+  }
+
+  private Integer parseQuestionCount(String input) {
+    try {
+      int value = Integer.parseInt(input);
+      if (value < 10 || value > 30) {
+        System.out.println("题目数量必须在10到30之间，请重新输入。");
+        return null;
+      }
+      return value;
+    } catch (NumberFormatException exception) {
+      System.out.println("请输入有效的数字或切换命令。");
+      return null;
+    }
+  }
+
+  private void generateAndPersistQuestions(
+      UserAccount account,
+      DifficultyLevel level,
+      int questionCount,
+      Set<String> existingQuestions) {
+    try {
+      var questions =
+          questionGenerationService
+              .generateUniqueQuestions(level, questionCount, existingQuestions);
+      Path outputPath = questionStorageService.saveQuestions(account.username(), questions);
+      existingQuestions.addAll(questions);
+      System.out.println(
+          "已生成"
+              + questionCount
+              + "道"
+              + level.getDisplayName()
+              + "数学题目，保存在："
+              + outputPath);
+    } catch (IllegalStateException exception) {
+      System.out.println("生成题目失败，请稍后重试。");
+    } catch (IOException exception) {
+      System.out.println("保存题目失败，请检查存储目录是否可写。");
+    }
+  }
+
+  private Set<String> loadExistingQuestions(String username) {
+    try {
+      return questionStorageService.loadExistingQuestions(username);
+    } catch (IOException exception) {
+      System.out.println("读取历史题目失败，将仅针对本次生成查重。");
+      return new HashSet<>();
+    }
+  }
+}
diff --git a/src/com/personalproject/auth/AccountRepository.java b/src/com/personalproject/auth/AccountRepository.java
new file mode 100644
index 0000000..9c2f379
--- /dev/null
+++ b/src/com/personalproject/auth/AccountRepository.java
@@ -0,0 +1,51 @@
+package com.personalproject.auth;
+
+import com.personalproject.model.DifficultyLevel;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+
+/**
+ * 存放预设教师账号并提供认证查询能力。
+ */
+public final class AccountRepository {
+  private final Map<String, UserAccount> accounts = new HashMap<>();
+
+  public AccountRepository() {
+    registerPrimaryAccounts();
+    registerMiddleSchoolAccounts();
+    registerHighSchoolAccounts();
+  }
+
+  public Optional<UserAccount> authenticate(String username, String password) {
+    if (username == null || password == null) {
+      return Optional.empty();
+    }
+    UserAccount account = accounts.get(username.trim());
+    if (account == null) {
+      return Optional.empty();
+    }
+    if (!account.password().equals(password.trim())) {
+      return Optional.empty();
+    }
+    return Optional.of(account);
+  }
+
+  private void registerPrimaryAccounts() {
+    accounts.put("张三1", new UserAccount("张三1", "123", DifficultyLevel.PRIMARY));
+    accounts.put("张三2", new UserAccount("张三2", "123", DifficultyLevel.PRIMARY));
+    accounts.put("张三3", new UserAccount("张三3", "123", DifficultyLevel.PRIMARY));
+  }
+
+  private void registerMiddleSchoolAccounts() {
+    accounts.put("李四1", new UserAccount("李四1", "123", DifficultyLevel.MIDDLE));
+    accounts.put("李四2", new UserAccount("李四2", "123", DifficultyLevel.MIDDLE));
+    accounts.put("李四3", new UserAccount("李四3", "123", DifficultyLevel.MIDDLE));
+  }
+
+  private void registerHighSchoolAccounts() {
+    accounts.put("王五1", new UserAccount("王五1", "123", DifficultyLevel.HIGH));
+    accounts.put("王五2", new UserAccount("王五2", "123", DifficultyLevel.HIGH));
+    accounts.put("王五3", new UserAccount("王五3", "123", DifficultyLevel.HIGH));
+  }
+}
diff --git a/src/com/personalproject/auth/UserAccount.java b/src/com/personalproject/auth/UserAccount.java
new file mode 100644
index 0000000..08d11ef
--- /dev/null
+++ b/src/com/personalproject/auth/UserAccount.java
@@ -0,0 +1,9 @@
+package com.personalproject.auth;
+
+import com.personalproject.model.DifficultyLevel;
+
+/**
+ * 不可变的账号定义。
+ */
+public record UserAccount(String username, String password, DifficultyLevel difficultyLevel) {
+}
diff --git a/src/com/personalproject/generator/HighSchoolQuestionGenerator.java b/src/com/personalproject/generator/HighSchoolQuestionGenerator.java
new file mode 100644
index 0000000..3240cf5
--- /dev/null
+++ b/src/com/personalproject/generator/HighSchoolQuestionGenerator.java
@@ -0,0 +1,36 @@
+package com.personalproject.generator;
+
+import java.util.Random;
+
+/**
+ * 生成至少包含一种三角函数的高中难度题目表达式。
+ */
+public final class HighSchoolQuestionGenerator implements QuestionGenerator {
+  private static final String[] OPERATORS = {"+", "-", "*", "/"};
+  private static final String[] TRIG_FUNCTIONS = {"sin", "cos", "tan"};
+
+  @Override
+  public String generateQuestion(Random random) {
+    int operandCount = random.nextInt(5) + 1;
+    String[] operands = new String[operandCount];
+    for (int index = 0; index < operandCount; index++) {
+      operands[index] = String.valueOf(random.nextInt(100) + 1);
+    }
+    int specialIndex = random.nextInt(operandCount);
+    String function = TRIG_FUNCTIONS[random.nextInt(TRIG_FUNCTIONS.length)];
+    operands[specialIndex] = function + '(' + operands[specialIndex] + ')';
+    StringBuilder builder = new StringBuilder();
+    for (int index = 0; index < operandCount; index++) {
+      if (index > 0) {
+        String operator = OPERATORS[random.nextInt(OPERATORS.length)];
+        builder.append(' ').append(operator).append(' ');
+      }
+      builder.append(operands[index]);
+    }
+    String expression = builder.toString();
+    if (operandCount > 1 && random.nextBoolean()) {
+      return '(' + expression + ')';
+    }
+    return expression;
+  }
+}
diff --git a/src/com/personalproject/generator/MiddleSchoolQuestionGenerator.java b/src/com/personalproject/generator/MiddleSchoolQuestionGenerator.java
new file mode 100644
index 0000000..4b3dba9
--- /dev/null
+++ b/src/com/personalproject/generator/MiddleSchoolQuestionGenerator.java
@@ -0,0 +1,38 @@
+package com.personalproject.generator;
+
+import java.util.Random;
+
+/**
+ * 生成包含平方或开根号运算的初中难度题目表达式。
+ */
+public final class MiddleSchoolQuestionGenerator implements QuestionGenerator {
+  private static final String[] OPERATORS = {"+", "-", "*", "/"};
+
+  @Override
+  public String generateQuestion(Random random) {
+    int operandCount = random.nextInt(5) + 1;
+    String[] operands = new String[operandCount];
+    for (int index = 0; index < operandCount; index++) {
+      operands[index] = String.valueOf(random.nextInt(100) + 1);
+    }
+    int specialIndex = random.nextInt(operandCount);
+    if (random.nextBoolean()) {
+      operands[specialIndex] = '(' + operands[specialIndex] + ")^2";
+    } else {
+      operands[specialIndex] = "sqrt(" + operands[specialIndex] + ')';
+    }
+    StringBuilder builder = new StringBuilder();
+    for (int index = 0; index < operandCount; index++) {
+      if (index > 0) {
+        String operator = OPERATORS[random.nextInt(OPERATORS.length)];
+        builder.append(' ').append(operator).append(' ');
+      }
+      builder.append(operands[index]);
+    }
+    String expression = builder.toString();
+    if (operandCount > 1 && random.nextBoolean()) {
+      return '(' + expression + ')';
+    }
+    return expression;
+  }
+}
diff --git a/src/com/personalproject/generator/PrimaryQuestionGenerator.java b/src/com/personalproject/generator/PrimaryQuestionGenerator.java
new file mode 100644
index 0000000..e0e0080
--- /dev/null
+++ b/src/com/personalproject/generator/PrimaryQuestionGenerator.java
@@ -0,0 +1,29 @@
+package com.personalproject.generator;
+
+import java.util.Random;
+
+/**
+ * 生成包含基础四则运算的小学难度题目表达式。
+ */
+public final class PrimaryQuestionGenerator implements QuestionGenerator {
+  private static final String[] OPERATORS = {"+", "-", "*", "/"};
+
+  @Override
+  public String generateQuestion(Random random) {
+    int operandCount = random.nextInt(5) + 1;
+    StringBuilder builder = new StringBuilder();
+    for (int index = 0; index < operandCount; index++) {
+      if (index > 0) {
+        String operator = OPERATORS[random.nextInt(OPERATORS.length)];
+        builder.append(' ').append(operator).append(' ');
+      }
+      int value = random.nextInt(100) + 1;
+      builder.append(value);
+    }
+    String expression = builder.toString();
+    if (operandCount > 1 && random.nextBoolean()) {
+      return '(' + expression + ')';
+    }
+    return expression;
+  }
+}
diff --git a/src/com/personalproject/generator/QuestionGenerator.java b/src/com/personalproject/generator/QuestionGenerator.java
new file mode 100644
index 0000000..9f346cd
--- /dev/null
+++ b/src/com/personalproject/generator/QuestionGenerator.java
@@ -0,0 +1,10 @@
+package com.personalproject.generator;
+
+import java.util.Random;
+
+/**
+ * 负责生成单条数学题目的表达式。
+ */
+public interface QuestionGenerator {
+  String generateQuestion(Random random);
+}
diff --git a/src/com/personalproject/model/DifficultyLevel.java b/src/com/personalproject/model/DifficultyLevel.java
new file mode 100644
index 0000000..5592801
--- /dev/null
+++ b/src/com/personalproject/model/DifficultyLevel.java
@@ -0,0 +1,38 @@
+package com.personalproject.model;
+
+import java.util.Optional;
+
+/**
+ * 系统支持的出题难度级别。
+ */
+public enum DifficultyLevel {
+  PRIMARY("小学"),
+  MIDDLE("初中"),
+  HIGH("高中");
+
+  private final String displayName;
+
+  DifficultyLevel(String displayName) {
+    this.displayName = displayName;
+  }
+
+  public String getDisplayName() {
+    return displayName;
+  }
+
+  public static Optional<DifficultyLevel> fromDisplayName(String name) {
+    if (name == null) {
+      return Optional.empty();
+    }
+    String trimmed = name.trim();
+    if (trimmed.isEmpty()) {
+      return Optional.empty();
+    }
+    for (DifficultyLevel level : values()) {
+      if (level.displayName.equals(trimmed)) {
+        return Optional.of(level);
+      }
+    }
+    return Optional.empty();
+  }
+}
diff --git a/src/com/personalproject/service/QuestionGenerationService.java b/src/com/personalproject/service/QuestionGenerationService.java
new file mode 100644
index 0000000..ca49ed2
--- /dev/null
+++ b/src/com/personalproject/service/QuestionGenerationService.java
@@ -0,0 +1,55 @@
+package com.personalproject.service;
+
+import com.personalproject.generator.QuestionGenerator;
+import com.personalproject.model.DifficultyLevel;
+import java.security.SecureRandom;
+import java.util.ArrayList;
+import java.util.EnumMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Random;
+import java.util.Set;
+
+/**
+ * 负责批量生成题目并避免与历史题库重复。
+ */
+public final class QuestionGenerationService {
+  private static final int MAX_ATTEMPTS = 10_000;
+  private final Map<DifficultyLevel, QuestionGenerator> generators;
+  private final Random random = new SecureRandom();
+
+  public QuestionGenerationService(Map<DifficultyLevel, QuestionGenerator> generatorMap) {
+    generators = new EnumMap<>(DifficultyLevel.class);
+    generators.putAll(generatorMap);
+  }
+
+  public List<String> generateUniqueQuestions(
+      DifficultyLevel level, int count, Set<String> existingQuestions) {
+    QuestionGenerator generator = generators.get(level);
+    if (generator == null) {
+      throw new IllegalArgumentException("Unsupported difficulty level: " + level);
+    }
+    Set<String> produced = new HashSet<>();
+    List<String> results = new ArrayList<>();
+    int attempts = 0;
+    while (results.size() < count) {
+      if (attempts >= MAX_ATTEMPTS) {
+        throw new IllegalStateException("Unable to generate enough unique questions.");
+      }
+      attempts++;
+      String question = generator.generateQuestion(random).trim();
+      if (question.isEmpty()) {
+        continue;
+      }
+      if (existingQuestions.contains(question)) {
+        continue;
+      }
+      if (!produced.add(question)) {
+        continue;
+      }
+      results.add(question);
+    }
+    return results;
+  }
+}
diff --git a/src/com/personalproject/storage/QuestionStorageService.java b/src/com/personalproject/storage/QuestionStorageService.java
new file mode 100644
index 0000000..4ce319e
--- /dev/null
+++ b/src/com/personalproject/storage/QuestionStorageService.java
@@ -0,0 +1,85 @@
+package com.personalproject.storage;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.nio.file.StandardOpenOption;
+import java.time.LocalDateTime;
+import java.time.format.DateTimeFormatter;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Stream;
+
+/**
+ * 负责保存生成的题目并维护查重信息。
+ */
+public final class QuestionStorageService {
+  private static final String BASE_DIRECTORY = "generated_questions";
+  private static final DateTimeFormatter FORMATTER =
+      DateTimeFormatter.ofPattern("yyyy-MM-dd-HH-mm-ss");
+
+  public Set<String> loadExistingQuestions(String username) throws IOException {
+    Path accountDirectory = getAccountDirectory(username);
+    Set<String> questions = new HashSet<>();
+    if (!Files.exists(accountDirectory)) {
+      return questions;
+    }
+    try (Stream<Path> paths = Files.list(accountDirectory)) {
+      paths
+          .filter(path -> path.getFileName().toString().endsWith(".txt"))
+          .sorted()
+          .forEach(path -> readQuestionsFromFile(path, questions));
+    }
+    return questions;
+  }
+
+  public Path saveQuestions(String username, List<String> questions) throws IOException {
+    Path accountDirectory = getAccountDirectory(username);
+    Files.createDirectories(accountDirectory);
+    String fileName = FORMATTER.format(LocalDateTime.now()) + ".txt";
+    Path outputFile = accountDirectory.resolve(fileName);
+    StringBuilder builder = new StringBuilder();
+    for (int index = 0; index < questions.size(); index++) {
+      String question = questions.get(index);
+      builder
+          .append(index + 1)
+          .append(". ")
+          .append(question)
+          .append(System.lineSeparator())
+          .append(System.lineSeparator());
+    }
+    Files.writeString(
+        outputFile, builder.toString(), StandardCharsets.UTF_8, StandardOpenOption.CREATE_NEW);
+    return outputFile;
+  }
+
+  private Path getAccountDirectory(String username) {
+    return Paths.get(BASE_DIRECTORY, username);
+  }
+
+  private void readQuestionsFromFile(Path path, Set<String> questions) {
+    try {
+      List<String> lines = Files.readAllLines(path, StandardCharsets.UTF_8);
+      for (String line : lines) {
+        String trimmed = line.trim();
+        if (trimmed.isEmpty()) {
+          continue;
+        }
+        int dotIndex = trimmed.indexOf('.');
+        if (dotIndex >= 0 && dotIndex + 1 < trimmed.length()) {
+          String question = trimmed.substring(dotIndex + 1).trim();
+          if (!question.isEmpty()) {
+            questions.add(question);
+          }
+        } else {
+          questions.add(trimmed);
+        }
+      }
+    } catch (IOException exception) {
+      // 继续处理其他文件，如有需要可在此处添加日志。
+    }
+  }
+}