diff --git a/README.md b/README.md
deleted file mode 100644
index 02cbfde..0000000
--- a/README.md
+++ /dev/null
@@ -1,2 +0,0 @@
-# double_program
-
diff --git a/doc/run_environment.md b/doc/run_environment.md
new file mode 100644
index 0000000..c0edbf4
--- /dev/null
+++ b/doc/run_environment.md
@@ -0,0 +1,6 @@
+**结对编程项目**
+
+操作系统：  Windows11 22H4  
+编码语言：  python3.8  
+中文编码格式：  UTF-8  
+个人项目参考：  张勇进的个人项目
\ No newline at end of file
diff --git a/src/main.py b/src/main.py
new file mode 100644
index 0000000..f8c1d40
--- /dev/null
+++ b/src/main.py
@@ -0,0 +1,790 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+"""
+单文件桌面应用：小初高数学练习（含注册/邮箱验证码、密码规则、题目自动生成）
+修改点：
+- 每道题操作数数量为 1-5（随机），操作数取值 1-100
+- 登录界面支持 使用 用户名 或 邮箱 登录
+- 其它功能保留：注册（邮箱验证码）、激活并设置密码、修改密码、选择学段与题量、自动生成题目、逐题答题、评分
+注意：
+- 请替换 SMTP 配置为有效账户或在无法发送邮件时调整 send_verification_email 为测试模式。
+- Python 3.8+
+"""
+
+import tkinter as tk
+from tkinter import messagebox, simpledialog, scrolledtext
+import json
+import os
+import secrets
+import hashlib
+import binascii
+import random
+import re
+import math
+import threading
+from datetime import datetime, timedelta
+import smtplib
+from email.mime.text import MIMEText
+
+# ---------------- 配置 ----------------
+USERS_FILE = "users.json"
+QUESTION_FILES = {
+    "小学": "questions_primary.json",
+    "初中": "questions_middle.json",
+    "高中": "questions_high.json",
+}
+LOG_FILE = "app_log.txt"
+
+# SMTP 配置 —— 请替换为可用的 SMTP 服务账号/密码/端口
+SMTP_SERVER = "smtp.126.com"
+SMTP_PORT = 25
+SENDER_EMAIL = "hape233@126.com"      # <-- 请替换
+SENDER_PASSWORD = "ZKcbV37TdRwgnsZC"  # <-- 请替换或使用授权码
+
+CODE_TTL_SECONDS = 300   # 验证码有效期 5 分钟
+SEND_COOLDOWN = 60       # 发送按钮冷却 60 秒
+MAX_QUESTIONS = 20       # 题目上限
+DEFAULT_QUESTIONS = 3    # 默认题目数
+
+WINDOW_W = 820
+WINDOW_H = 620
+
+# 题目生成参数
+MIN_OPERANDS = 1
+MAX_OPERANDS = 5
+OPERAND_MIN = 1
+OPERAND_MAX = 100
+# --------------------------------------
+
+# ----------------- 辅助与存储 -----------------
+def log(msg: str):
+    with open(LOG_FILE, "a", encoding="utf-8") as f:
+        f.write(f"{datetime.utcnow().isoformat()} {msg}\n")
+
+def ensure_files_exist():
+    # users file
+    if not os.path.exists(USERS_FILE):
+        with open(USERS_FILE, "w", encoding="utf-8") as f:
+            json.dump([], f, ensure_ascii=False, indent=2)
+    # question files
+    for k, p in QUESTION_FILES.items():
+        if not os.path.exists(p):
+            with open(p, "w", encoding="utf-8") as f:
+                json.dump([], f, ensure_ascii=False, indent=2)
+
+# User store
+class UserStore:
+    def __init__(self, path=USERS_FILE):
+        self.path = path
+        self._load()
+
+    def _load(self):
+        try:
+            with open(self.path, "r", encoding="utf-8") as f:
+                self.users = json.load(f)
+        except Exception:
+            self.users = []
+
+    def _save(self):
+        with open(self.path, "w", encoding="utf-8") as f:
+            json.dump(self.users, f, ensure_ascii=False, indent=2)
+
+    def find_by_email(self, email: str):
+        for u in self.users:
+            if u.get("email") == email:
+                return u
+        return None
+
+    def find_by_username(self, username: str):
+        for u in self.users:
+            if u.get("username") == username:
+                return u
+        return None
+
+    def find(self, key: str):
+        # try email first, then username
+        u = self.find_by_email(key)
+        if u:
+            return u
+        return self.find_by_username(key)
+
+    def add_or_update(self, user: dict):
+        existing = self.find_by_email(user["email"])
+        if existing:
+            existing.update(user)
+        else:
+            self.users.append(user)
+        self._save()
+
+# Question store
+class QuestionStore:
+    def __init__(self, files_map=QUESTION_FILES):
+        self.files_map = files_map
+
+    def load(self, grade: str):
+        p = self.files_map.get(grade)
+        try:
+            with open(p, "r", encoding="utf-8") as f:
+                return json.load(f)
+        except Exception:
+            return []
+
+    def save(self, grade: str, qs):
+        p = self.files_map.get(grade)
+        with open(p, "w", encoding="utf-8") as f:
+            json.dump(qs, f, ensure_ascii=False, indent=2)
+
+# ----------------- 验证码管理 & 密码哈希 -----------------
+EMAIL_RE = re.compile(r"^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}$")
+def is_valid_email(e: str) -> bool:
+    return bool(EMAIL_RE.match(e or ""))
+
+class VerificationManager:
+    def __init__(self):
+        self.store = {}  # email -> (code, expiry)
+
+    def gen(self, email):
+        code = f"{random.randint(100000, 999999)}"
+        expiry = datetime.utcnow() + timedelta(seconds=CODE_TTL_SECONDS)
+        self.store[email] = (code, expiry)
+        return code
+
+    def verify(self, email, code):
+        rec = self.store.get(email)
+        if not rec:
+            return False, "未发送验证码"
+        real, expiry = rec
+        if datetime.utcnow() > expiry:
+            return False, "验证码已过期"
+        if not secrets.compare_digest(real, code):
+            return False, "验证码不匹配"
+        # 删除以防二次使用
+        del self.store[email]
+        return True, "验证成功"
+
+verif_mgr = VerificationManager()
+
+def hash_password(password: str, salt: bytes = None):
+    if salt is None:
+        salt = secrets.token_bytes(16)
+    dk = hashlib.pbkdf2_hmac("sha256", password.encode("utf-8"), salt, 100000)
+    return binascii.hexlify(dk).decode("utf-8"), binascii.hexlify(salt).decode("utf-8")
+
+def verify_password_hash(stored_hash, stored_salt, attempt):
+    try:
+        salt = binascii.unhexlify(stored_salt)
+        at_hash, _ = hash_password(attempt, salt)
+        return secrets.compare_digest(at_hash, stored_hash)
+    except Exception:
+        return False
+
+# ----------------- SMTP 发送 -----------------
+def send_verification_email(target_email: str, code: str):
+    """同步发送；上层在线程中调用"""
+    msg = MIMEText(f"您的注册码（6位）：{code}\n有效期 {CODE_TTL_SECONDS//60} 分钟。")
+    msg['Subject'] = "注册码"
+    msg['From'] = SENDER_EMAIL
+    msg['To'] = target_email
+    try:
+        server = smtplib.SMTP(SMTP_SERVER, SMTP_PORT, timeout=30)
+        try:
+            server.starttls()
+        except Exception:
+            pass
+        server.login(SENDER_EMAIL, SENDER_PASSWORD)
+        server.sendmail(SENDER_EMAIL, [target_email], msg.as_string())
+        try:
+            server.quit()
+        except Exception:
+            server.close()
+        log(f"Sent code {code} to {target_email}")
+        return True, "发送成功"
+    except Exception as e:
+        try:
+            server.close()
+        except:
+            pass
+        log(f"Failed send code to {target_email}: {e}")
+        return False, str(e)
+
+# ----------------- 题目生成（1~5 个操作数，操作数范围 1~100） -----------------
+def gen_id(prefix: str) -> str:
+    return f"{prefix}_{secrets.token_hex(4)}"
+
+def mk_options_from_number(correct_val, kind="int"):
+    # produce 4 unique options including correct
+    opts = []
+    if kind == "int":
+        corr = int(round(correct_val))
+        opts = [str(corr)]
+        attempts = 0
+        while len(opts) < 4 and attempts < 100:
+            delta = random.choice([-10, -6, -3, -2, -1, 1, 2, 3, 5, 8, 10])
+            candidate = corr + delta
+            if str(candidate) not in opts:
+                opts.append(str(candidate))
+            attempts += 1
+        while len(opts) < 4:
+            opts.append(str(corr + random.randint(11, 50)))
+        random.shuffle(opts)
+        return opts, opts.index(str(corr))
+    else:
+        # float
+        corr = float(correct_val)
+        corr_s = f"{corr:.3f}"
+        opts = [corr_s]
+        attempts = 0
+        while len(opts) < 4 and attempts < 200:
+            delta = random.choice([-0.8, -0.5, -0.3, -0.2, -0.1, 0.1, 0.2, 0.3, 0.5, 0.8])
+            cand = corr + delta
+            s = f"{cand:.3f}"
+            if s not in opts:
+                opts.append(s)
+            attempts += 1
+        while len(opts) < 4:
+            opts.append(f"{(corr + random.uniform(1.0,3.0)):.3f}")
+        random.shuffle(opts)
+        return opts, opts.index(corr_s)
+
+# 安全评估：表达式由程序生成，使用受限 eval 环境评估
+SAFE_EVAL_ENV = {"__builtins__": None, "sqrt": math.sqrt, "sin": math.sin, "cos": math.cos, "tan": math.tan, "pi": math.pi}
+
+def safe_eval(expr: str):
+    # 只包含数字、运算符、sqrt, sin, cos, tan, (, ), ^ 替换为 **
+    expr = expr.replace("^", "**")
+    return eval(expr, SAFE_EVAL_ENV, {})
+
+# 小学题：1~5 个操作数，运算符 + - * /，可能带一对括号
+def generate_primary_question():
+    n_ops = random.randint(MIN_OPERANDS, MAX_OPERANDS)  # number of operands
+    nums = [random.randint(OPERAND_MIN, OPERAND_MAX) for _ in range(n_ops)]
+    ops_list = [random.choice(['+', '-', '*', '/']) for _ in range(max(0, n_ops - 1))]
+    # Build expression, maybe with parentheses
+    parts = []
+    for i in range(n_ops):
+        parts.append(str(nums[i]))
+        if i < len(ops_list):
+            parts.append(ops_list[i])
+    expr = "".join(parts)
+    if n_ops >= 2 and random.choice([True, False]):
+        idx = random.randint(0, n_ops - 2)
+        parts = []
+        for i in range(n_ops):
+            p = str(nums[i])
+            if i == idx:
+                p = "(" + p
+            if i == idx + 1:
+                p = p + ")"
+            parts.append(p)
+            if i < len(ops_list):
+                parts.append(ops_list[i])
+        expr = "".join(parts)
+    # evaluate and prefer integer
+    val = None
+    for _ in range(60):
+        try:
+            v = safe_eval(expr)
+            if v is None or isinstance(v, complex):
+                raise ValueError
+            if isinstance(v, float):
+                v = int(round(v))
+            val = v
+            break
+        except Exception:
+            # regenerate simpler
+            n_ops = random.randint(MIN_OPERANDS, MAX_OPERANDS)
+            nums = [random.randint(OPERAND_MIN, OPERAND_MAX) for _ in range(n_ops)]
+            ops_list = [random.choice(['+', '-', '*', '/']) for _ in range(max(0, n_ops - 1))]
+            parts = []
+            for i in range(n_ops):
+                parts.append(str(nums[i]))
+                if i < len(ops_list):
+                    parts.append(ops_list[i])
+            expr = "".join(parts)
+    if val is None:
+        val = 0
+    opts, idx = mk_options_from_number(val, kind="int")
+    return {"id": gen_id("pri"), "grade": "小学", "stem": f"{expr} = ?", "options": opts, "answer_index": idx}
+
+# 初中题：至少包含平方或开根号 sqrt(...)
+def generate_middle_question():
+    use_sqrt = random.choice([True, False])
+    use_square = not use_sqrt if random.random() < 0.3 else random.choice([True, False])
+    n_ops = random.randint(MIN_OPERANDS, MAX_OPERANDS)
+    nums = [random.randint(OPERAND_MIN, OPERAND_MAX) for _ in range(n_ops)]
+    ops_list = [random.choice(['+', '-', '*', '/']) for _ in range(max(0, n_ops - 1))]
+    idx = random.randint(0, n_ops - 1)
+    if use_sqrt:
+        # try to use perfect square inside sometimes
+        inside = random.randint(1, 50)
+        if random.choice([True, False]):
+            nums[idx] = f"sqrt({inside*inside})"
+        else:
+            nums[idx] = f"sqrt({nums[idx]})"
+    else:
+        nums[idx] = f"({nums[idx]}**2)"
+    parts = []
+    for i in range(n_ops):
+        parts.append(str(nums[i]))
+        if i < len(ops_list):
+            parts.append(ops_list[i])
+    expr = "".join(parts)
+    val = None
+    for _ in range(60):
+        try:
+            v = safe_eval(expr)
+            if v is None or isinstance(v, complex):
+                raise ValueError
+            val = v
+            break
+        except Exception:
+            n_ops = random.randint(MIN_OPERANDS, MAX_OPERANDS)
+            nums = [random.randint(OPERAND_MIN, OPERAND_MAX) for _ in range(n_ops)]
+            ops_list = [random.choice(['+', '-', '*', '/']) for _ in range(max(0, n_ops - 1))]
+            idx = random.randint(0, n_ops - 1)
+            if random.choice([True, False]):
+                nums[idx] = f"sqrt({nums[idx]*nums[idx]})"
+            else:
+                nums[idx] = f"({nums[idx]}**2)"
+            parts = []
+            for i in range(n_ops):
+                parts.append(str(nums[i]))
+                if i < len(ops_list):
+                    parts.append(ops_list[i])
+            expr = "".join(parts)
+    if val is None:
+        val = 0
+    if isinstance(val, float) and abs(val - round(val)) > 1e-9:
+        opts, idx = mk_options_from_number(val, kind="float")
+    else:
+        opts, idx = mk_options_from_number(val, kind="int")
+    return {"id": gen_id("mid"), "grade": "初中", "stem": f"{expr} = ?", "options": opts, "answer_index": idx}
+
+# 高中题：至少包含 sin/cos/tan（使用角度），并可包含 1~5 个操作数
+def generate_high_question():
+    func = random.choice(["sin", "cos", "tan"])
+    n_ops = random.randint(MIN_OPERANDS, MAX_OPERANDS)
+    nums = [random.randint(OPERAND_MIN, OPERAND_MAX) for _ in range(n_ops)]
+    ops_list = [random.choice(['+', '-', '*', '/']) for _ in range(max(0, n_ops - 1))]
+    idx = random.randint(0, n_ops - 1)
+    angle = random.choice([0, 30, 45, 60, 90, 120, 135, 150, 180, 210, 225, 240, 270, 300, 315, 330])
+    nums[idx] = f"{func}(pi*{angle}/180)"
+    parts = []
+    for i in range(n_ops):
+        parts.append(str(nums[i]))
+        if i < len(ops_list):
+            parts.append(ops_list[i])
+    expr = "".join(parts)
+    val = None
+    for _ in range(60):
+        try:
+            v = safe_eval(expr)
+            if v is None or isinstance(v, complex):
+                raise ValueError
+            val = v
+            break
+        except Exception:
+            n_ops = random.randint(MIN_OPERANDS, MAX_OPERANDS)
+            nums = [random.randint(OPERAND_MIN, OPERAND_MAX) for _ in range(n_ops)]
+            ops_list = [random.choice(['+', '-', '*', '/']) for _ in range(max(0, n_ops - 1))]
+            idx = random.randint(0, n_ops - 1)
+            angle = random.choice([30,45,60,90,120])
+            func = random.choice(["sin", "cos", "tan"])
+            nums[idx] = f"{func}(pi*{angle}/180)"
+            parts = []
+            for i in range(n_ops):
+                parts.append(str(nums[i]))
+                if i < len(ops_list):
+                    parts.append(ops_list[i])
+            expr = "".join(parts)
+    if val is None:
+        val = 0.0
+    opts, idx = mk_options_from_number(val, kind="float")
+    stem = f"{expr} = ? (保留3位小数)"
+    return {"id": gen_id("high"), "grade": "高中", "stem": stem, "options": opts, "answer_index": idx}
+
+# Ensure enough questions in file; auto-generate and append if insufficient
+def ensure_questions_for_grade(grade: str, needed: int, qstore: QuestionStore):
+    qs = qstore.load(grade)
+    if len(qs) >= needed:
+        return qs
+    to_gen = needed - len(qs)
+    gen = []
+    for _ in range(to_gen):
+        if grade == "小学":
+            gen.append(generate_primary_question())
+        elif grade == "初中":
+            gen.append(generate_middle_question())
+        else:
+            gen.append(generate_high_question())
+    qs.extend(gen)
+    qstore.save(grade, qs)
+    log(f"Auto-generated {len(gen)} questions for {grade}")
+    return qs
+
+# ----------------- 服务逻辑（注册/激活/登录/改密） -----------------
+class AuthService:
+    def __init__(self, store: UserStore):
+        self.store = store
+
+    def send_code(self, email: str):
+        if not is_valid_email(email):
+            return False, "邮箱格式不正确"
+        u = self.store.find_by_email(email)
+        if u and u.get("activated"):
+            return False, "该邮箱已注册并激活"
+        code = verif_mgr.gen(email)
+        ok, msg = send_verification_email(email, code)
+        return ok, msg
+
+    def register_with_code(self, email: str, code: str, username: str, password: str):
+        if not is_valid_email(email):
+            return False, "邮箱格式不正确"
+        if not username:
+            return False, "用户名不能为空"
+        # check username uniqueness
+        existing_user = self.store.find_by_username(username)
+        if existing_user and existing_user.get("email") != email:
+            return False, "用户名已被占用"
+        if not (6 <= len(password) <= 10 and any(c.isupper() for c in password) and any(c.islower() for c in password) and any(c.isdigit() for c in password)):
+            return False, "密码规则不满足（6-10位，含大小写字母和数字）"
+        ok, msg = verif_mgr.verify(email, code)
+        if not ok:
+            return False, msg
+        ph, salt = hash_password(password)
+        rec = {
+            "email": email,
+            "username": username,
+            "password_hash": ph,
+            "salt": salt,
+            "activated": True,
+            "created_at": datetime.utcnow().isoformat()
+        }
+        self.store.add_or_update(rec)
+        log(f"user registered: {email} / {username}")
+        return True, "注册并设置密码成功"
+
+    def login(self, key: str, password: str):
+        # key can be email or username
+        u = self.store.find(key)
+        if not u:
+            return False, "未找到该用户"
+        if not u.get("activated"):
+            return False, "该账号未激活"
+        if not verify_password_hash(u.get("password_hash"), u.get("salt"), password):
+            return False, "密码错误"
+        return True, u
+
+    def change_password(self, email: str, old_pw: str, new_pw: str):
+        u = self.store.find_by_email(email)
+        if not u:
+            return False, "未找到用户"
+        if not verify_password_hash(u.get("password_hash"), u.get("salt"), old_pw):
+            return False, "原密码错误"
+        if not (6 <= len(new_pw) <= 10 and any(c.isupper() for c in new_pw) and any(c.islower() for c in new_pw) and any(c.isdigit() for c in new_pw)):
+            return False, "新密码不符合规则"
+        ph, salt = hash_password(new_pw)
+        u.update({"password_hash": ph, "salt": salt})
+        self.store._save()
+        log(f"user changed password: {email}")
+        return True, "修改成功"
+
+# ----------------- GUI -----------------
+class MathApp:
+    def __init__(self, root):
+        self.root = root
+        self.root.title("小初高数学练习")
+        self.root.geometry(f"{WINDOW_W}x{WINDOW_H}")
+        ensure_files_exist()
+        self.user_store = UserStore()
+        self.qstore = QuestionStore()
+        self.auth = AuthService(self.user_store)
+        self.current_user = None  # user dict
+        self.current_exam = None
+        self.build_main()
+
+    def clear(self):
+        for w in self.root.winfo_children():
+            w.destroy()
+
+    def build_main(self):
+        self.clear()
+        frm = tk.Frame(self.root, padx=20, pady=20)
+        frm.pack(fill="both", expand=True)
+        tk.Label(frm, text="数学学习应用", font=("Arial", 18)).pack(pady=12)
+        tk.Button(frm, text="注册", width=40, command=self.ui_register_flow).pack(pady=6)
+        tk.Button(frm, text="登录", width=40, command=self.ui_login).pack(pady=6)
+        tk.Button(frm, text="退出", width=40, command=self.root.quit).pack(pady=6)
+
+    # ----- 注册流程 -----
+    def ui_register_flow(self):
+        self.clear()
+        fr = tk.Frame(self.root, padx=12, pady=12)
+        fr.pack(fill="both", expand=True)
+
+        tk.Label(fr, text="邮箱（注册邮箱）:").grid(row=0, column=0, sticky="e")
+        email_var = tk.StringVar()
+        email_entry = tk.Entry(fr, textvariable=email_var, width=36)
+        email_entry.grid(row=0, column=1, padx=6)
+        send_btn = tk.Button(fr, text="发送验证码")
+        send_btn.grid(row=0, column=2, padx=6)
+
+        tk.Label(fr, text="验证码:").grid(row=1, column=0, sticky="e")
+        code_var = tk.StringVar()
+        code_entry = tk.Entry(fr, textvariable=code_var, width=20)
+        code_entry.grid(row=1, column=1, padx=6)
+
+        tk.Label(fr, text="用户名:").grid(row=2, column=0, sticky="e")
+        username_var = tk.StringVar()
+        username_entry = tk.Entry(fr, textvariable=username_var, width=30)
+        username_entry.grid(row=2, column=1, padx=6)
+
+        tk.Label(fr, text="密码:").grid(row=3, column=0, sticky="e")
+        pw_var = tk.StringVar()
+        pw_entry = tk.Entry(fr, textvariable=pw_var, show="*", width=30)
+        pw_entry.grid(row=3, column=1, padx=6)
+
+        tk.Label(fr, text="确认密码:").grid(row=4, column=0, sticky="e")
+        pw2_var = tk.StringVar()
+        pw2_entry = tk.Entry(fr, textvariable=pw2_var, show="*", width=30)
+        pw2_entry.grid(row=4, column=1, padx=6)
+
+        btn_fr = tk.Frame(fr)
+        btn_fr.grid(row=6, column=0, columnspan=3, pady=18)
+        tk.Button(btn_fr, text="确定", width=12, command=lambda: on_confirm()).pack(side="left", padx=8)
+        tk.Button(btn_fr, text="返回", width=12, command=self.build_main).pack(side="left", padx=8)
+
+        fr.grid_columnconfigure(1, weight=1)
+
+        cooldown = {"left": 0, "timer": None}
+
+        def update_send_btn():
+            if cooldown["left"] > 0:
+                send_btn.config(text=f"重新发送({cooldown['left']})", state="disabled")
+            else:
+                send_btn.config(text="发送验证码", state="normal")
+
+        def countdown_tick():
+            if cooldown["left"] <= 0:
+                update_send_btn()
+                return
+            cooldown["left"] -= 1
+            update_send_btn()
+            cooldown["timer"] = self.root.after(1000, countdown_tick)
+
+        def on_send():
+            email = email_var.get().strip()
+            if not is_valid_email(email):
+                messagebox.showwarning("邮箱错误", "请输入正确的邮箱地址", parent=self.root)
+                return
+            # generate and send code asynchronously
+            def worker():
+                send_btn.config(state="disabled", text="发送中...")
+                ok, msg = self.auth.send_code(email)
+                if ok:
+                    messagebox.showinfo("发送成功", f"验证码已发送到 {email}（若未收到, 请检查垃圾邮件）。", parent=self.root)
+                    cooldown["left"] = SEND_COOLDOWN
+                    countdown_tick()
+                else:
+                    messagebox.showerror("发送失败", f"发送失败: {msg}", parent=self.root)
+                update_send_btn()
+            threading.Thread(target=worker, daemon=True).start()
+
+        send_btn.config(command=on_send)
+
+        def on_confirm():
+            email = email_var.get().strip()
+            code = code_var.get().strip()
+            username = username_var.get().strip()
+            pw = pw_var.get()
+            pw2 = pw2_var.get()
+            if not is_valid_email(email):
+                messagebox.showwarning("错误", "请输入合法邮箱", parent=self.root); return
+            if not code:
+                messagebox.showwarning("错误", "请输入验证码", parent=self.root); return
+            if not username:
+                messagebox.showwarning("错误", "请输入用户名", parent=self.root); return
+            if not pw or not pw2:
+                messagebox.showwarning("错误", "请输入密码并确认", parent=self.root); return
+            if pw != pw2:
+                messagebox.showwarning("错误", "两次密码不一致", parent=self.root); return
+            if not (6 <= len(pw) <= 10 and any(c.isupper() for c in pw) and any(c.islower() for c in pw) and any(c.isdigit() for c in pw)):
+                messagebox.showwarning("错误", "密码需6-10位，且包含大写、小写字母与数字", parent=self.root); return
+            ok, msg = self.auth.register_with_code(email, code, username, pw)
+            if not ok:
+                messagebox.showerror("失败", msg, parent=self.root); return
+            messagebox.showinfo("成功", "注册并设置密码成功，跳转到选择界面", parent=self.root)
+            # login and go to choice screen
+            self.current_user = self.user_store.find_by_email(email)
+            self.build_choice_screen()
+
+    # ----- 登录界面（用户名/邮箱登录） -----
+    def ui_login(self):
+        self.clear()
+        fr = tk.Frame(self.root, padx=12, pady=12)
+        fr.pack(fill="both", expand=True)
+        tk.Label(fr, text="登录", font=("Arial", 16)).pack(pady=8)
+        tk.Label(fr, text="用户名/邮箱：").pack(anchor="w")
+        key_var = tk.StringVar()
+        tk.Entry(fr, textvariable=key_var, width=50).pack(pady=4)
+        tk.Label(fr, text="密码：").pack(anchor="w")
+        pw_var = tk.StringVar()
+        tk.Entry(fr, textvariable=pw_var, show="*", width=50).pack(pady=4)
+        btn_fr = tk.Frame(fr); btn_fr.pack(pady=12)
+        def do_login():
+            key = key_var.get().strip()
+            pw = pw_var.get()
+            if not key:
+                messagebox.showwarning("输入错误", "请输入用户名或邮箱", parent=self.root); return
+            ok, res = self.auth.login(key, pw)
+            if not ok:
+                messagebox.showerror("登录失败", res, parent=self.root); return
+            # res is user dict
+            self.current_user = res
+            messagebox.showinfo("登录成功", f"欢迎，{self.current_user.get('username')}", parent=self.root)
+            self.build_choice_screen()
+        tk.Button(btn_fr, text="登录", width=12, command=do_login).pack(side="left", padx=6)
+        tk.Button(btn_fr, text="返回", width=12, command=self.build_main).pack(side="left", padx=6)
+
+    # ----- 选择学段与题量 -----
+    def build_choice_screen(self):
+        self.clear()
+        fr = tk.Frame(self.root, padx=12, pady=12)
+        fr.pack(fill="both", expand=True)
+        uname = self.current_user.get("username") if self.current_user else ""
+        email = self.current_user.get("email") if self.current_user else ""
+        tk.Label(fr, text=f"已登录: {uname} ({email})", font=("Arial", 12)).pack(anchor="w")
+        tk.Button(fr, text="修改密码", command=self.ui_change_password).pack(anchor="w", pady=4)
+        tk.Button(fr, text="注销", command=self.logout).pack(anchor="w", pady=4)
+        tk.Label(fr, text="请选择学段并输入题目数量（默认3，上限20）:", font=("Arial", 12)).pack(pady=8, anchor="w")
+        grade_var = tk.StringVar(value="小学")
+        for g in QUESTION_FILES.keys():
+            tk.Radiobutton(fr, text=g, variable=grade_var, value=g).pack(anchor="w")
+        num_entry = tk.Entry(fr, width=8)
+        num_entry.pack(pady=6, anchor="w")
+        num_entry.delete(0, "end"); num_entry.insert(0, str(DEFAULT_QUESTIONS))
+        def start():
+            try:
+                n = int(num_entry.get())
+                if n <= 0:
+                    raise ValueError()
+                if n > MAX_QUESTIONS:
+                    messagebox.showwarning("超过上限", f"题目数量上限为 {MAX_QUESTIONS}", parent=self.root); return
+            except Exception:
+                messagebox.showwarning("输入错误", "请输入正整数题目数量", parent=self.root); return
+            grade = grade_var.get()
+            qs = self.qstore.load(grade)
+            if len(qs) < n:
+                qs = ensure_questions_for_grade(grade, n, self.qstore)
+            chosen = random.sample(qs, n)
+            self.current_exam = {"grade": grade, "questions": chosen, "index": 0, "answers": [None]*n}
+            self.build_question_screen()
+        tk.Button(fr, text="开始做题", command=start).pack(pady=8)
+
+    def logout(self):
+        self.current_user = None
+        self.current_exam = None
+        self.build_main()
+
+    def ui_change_password(self):
+        if not self.current_user:
+            messagebox.showwarning("未登录", "请先登录", parent=self.root); return
+        old = simpledialog.askstring("修改密码", "请输入原密码：", show="*", parent=self.root)
+        if old is None:
+            return
+        new1 = simpledialog.askstring("新密码", "请输入新密码（6-10位，含大小写字母与数字）：", show="*", parent=self.root)
+        if new1 is None:
+            return
+        new2 = simpledialog.askstring("确认新密码", "请再次输入新密码：", show="*", parent=self.root)
+        if new2 is None:
+            return
+        if new1 != new2:
+            messagebox.showwarning("不一致", "两次新密码不一致", parent=self.root); return
+        ok, msg = self.auth.change_password(self.current_user.get("email"), old, new1)
+        if not ok:
+            messagebox.showerror("失败", msg, parent=self.root); return
+        messagebox.showinfo("成功", "密码修改成功", parent=self.root)
+
+    # ----- 题目界面 -----
+    def build_question_screen(self):
+        self.clear()
+        exam = self.current_exam
+        idx = exam["index"]
+        q = exam["questions"][idx]
+        fr = tk.Frame(self.root, padx=12, pady=12)
+        fr.pack(fill="both", expand=True)
+        header = tk.Label(fr, text=f"学段：{exam['grade']}    题目 {idx+1}/{len(exam['questions'])}", font=("Arial", 12))
+        header.pack(anchor="w")
+        stem = tk.Label(fr, text=q["stem"], font=("Arial", 14), wraplength=WINDOW_W-80, justify="left")
+        stem.pack(pady=8, anchor="w")
+        chosen_var = tk.IntVar(value=-1 if exam["answers"][idx] is None else exam["answers"][idx])
+        for i, opt in enumerate(q["options"]):
+            tk.Radiobutton(fr, text=opt, variable=chosen_var, value=i).pack(anchor="w")
+        nav = tk.Frame(fr); nav.pack(pady=10, anchor="w")
+        def save_choice():
+            v = chosen_var.get()
+            exam["answers"][idx] = None if v == -1 else int(v)
+            return True
+        def prev_q():
+            if idx == 0:
+                messagebox.showinfo("提示", "已经是第一题", parent=self.root); return
+            save_choice(); exam["index"] -= 1; self.build_question_screen()
+        def next_or_finish():
+            save_choice()
+            if idx + 1 < len(exam["questions"]):
+                exam["index"] += 1
+                self.build_question_screen()
+            else:
+                self.show_result_screen()
+        tk.Button(nav, text="上一题", command=prev_q).pack(side="left", padx=6)
+        tk.Button(nav, text="下一题/提交", command=next_or_finish).pack(side="left", padx=6)
+        tk.Button(nav, text="放弃并返回", command=self.build_choice_screen).pack(side="left", padx=6)
+
+    # ----- 结果界面 -----
+    def show_result_screen(self):
+        exam = self.current_exam
+        total = len(exam["questions"])
+        correct = 0
+        for i, q in enumerate(exam["questions"]):
+            ans = exam["answers"][i]
+            if ans is not None and ans == q["answer_index"]:
+                correct += 1
+        percent = round(correct / total * 100, 2) if total > 0 else 0.0
+        self.clear()
+        fr = tk.Frame(self.root, padx=12, pady=12)
+        fr.pack(fill="both", expand=True)
+        tk.Label(fr, text=f"考试结束 - 得分：{percent}%", font=("Arial", 14)).pack(pady=6)
+        tk.Label(fr, text=f"答对：{correct} / {total}").pack(pady=4)
+        def show_details():
+            win = tk.Toplevel(self.root); win.title("答题详情")
+            txt = scrolledtext.ScrolledText(win, width=100, height=30)
+            txt.pack(fill="both", expand=True)
+            for i, q in enumerate(exam["questions"]):
+                chosen = exam["answers"][i]
+                chosen_text = q["options"][chosen] if chosen is not None and 0 <= chosen < len(q["options"]) else "未作答"
+                correct_text = q["options"][q["answer_index"]]
+                status = "正确" if chosen == q["answer_index"] else "错误"
+                txt.insert("end", f"题 {i+1}: {q['stem']}\n你的答案: {chosen_text}\n正确答案: {correct_text}  [{status}]\n\n")
+            txt.config(state="disabled")
+        tk.Button(fr, text="查看答题详情", command=show_details).pack(pady=6)
+        tk.Button(fr, text="继续做题", command=self._continue_again).pack(pady=6)
+        tk.Button(fr, text="退出登录并返回主界面", command=self._logout_and_return).pack(pady=6)
+
+    def _continue_again(self):
+        self.current_exam = None
+        self.build_choice_screen()
+
+    def _logout_and_return(self):
+        self.current_user = None
+        self.current_exam = None
+        self.build_main()
+
+# ----------------- 初始化 -----------------
+def main():
+    ensure_files_exist()
+    root = tk.Tk()
+    app = MathApp(root)
+    root.mainloop()
+
+if __name__ == "__main__":
+    main()
\ No newline at end of file