{
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   "source": [
    "# Day 2 — Loops, Functions & Defensive Programming\n",
    "### Summer Coding & Cybersecurity Camp\n",
    "\n",
    "Yesterday we *broke* a calculator. Today we learn how to build programs that\n",
    "**refuse to break** — the heart of secure, professional code.\n",
    "\n",
    "**By the end of today you can:**\n",
    "- Repeat actions with `for` and `while` loops\n",
    "- Store collections in **lists** and **dictionaries**\n",
    "- Write reusable **functions**\n",
    "- Catch errors with `try / except` so programs fail *gracefully*\n",
    "- Keep asking until the user gives **valid** input (input validation)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "53640051",
   "metadata": {},
   "source": [
    "## 1. `while` loops — repeat until a condition changes"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "f85b5dfc",
   "metadata": {},
   "outputs": [],
   "source": [
    "count = 1\n",
    "while count <= 5:\n",
    "    print(\"Countdown:\", count)\n",
    "    count = count + 1\n",
    "print(\"Liftoff! 🚀\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "b3fe800e",
   "metadata": {},
   "source": [
    "## 2. `for` loops and `range()`"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "d8d97560",
   "metadata": {},
   "outputs": [],
   "source": [
    "for i in range(3):          # 0, 1, 2\n",
    "    print(\"Attempt number\", i + 1)\n",
    "\n",
    "for letter in \"code\":\n",
    "    print(letter)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "ce3ea78e",
   "metadata": {},
   "source": [
    "## 3. Lists — ordered collections"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "2041f2cd",
   "metadata": {},
   "outputs": [],
   "source": [
    "tasks = [\"learn python\", \"write secure code\", \"have fun\"]\n",
    "tasks.append(\"eat snacks\")\n",
    "\n",
    "print(\"Number of tasks:\", len(tasks))\n",
    "for t in tasks:\n",
    "    print(\"-\", t)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "a5de4a33",
   "metadata": {},
   "source": [
    "## 4. Dictionaries — labeled data (key → value)\n",
    "Dictionaries are everywhere in security: storing usernames mapped to data, settings,\n",
    "configuration, etc."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "94300ddb",
   "metadata": {},
   "outputs": [],
   "source": [
    "user = {\"name\": \"Sam\", \"role\": \"student\", \"logins\": 0}\n",
    "\n",
    "print(user[\"name\"])\n",
    "user[\"logins\"] = user[\"logins\"] + 1   # update a value\n",
    "print(\"Login count:\", user[\"logins\"])"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "28b5c696",
   "metadata": {},
   "source": [
    "## 5. Functions — package code so you can reuse it\n",
    "A function takes **inputs** (parameters), does work, and `return`s a result.\n",
    "Reusable functions are also *easier to secure*, because you fix a bug in **one** place."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "02d0e68d",
   "metadata": {},
   "outputs": [],
   "source": [
    "def double(number):\n",
    "    return number * 2\n",
    "\n",
    "print(double(10))\n",
    "print(double(7))"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "6f425ed7",
   "metadata": {},
   "source": [
    "## 6. 🔐 The fix: `try / except`\n",
    "Remember yesterday's crash? `try / except` lets us *attempt* something risky and\n",
    "catch the error instead of letting the whole program die."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "5e3ac49a",
   "metadata": {},
   "outputs": [],
   "source": [
    "text = input(\"Enter a number: \")\n",
    "\n",
    "try:\n",
    "    value = int(text)\n",
    "    print(\"Great, you entered:\", value)\n",
    "except ValueError:\n",
    "    print(\"⚠️ That wasn't a whole number — but I didn't crash!\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "9f3a1b2e",
   "metadata": {},
   "source": [
    "## 7. 🔐 Input validation: keep asking until it's valid\n",
    "Professional programs don't trust the first thing typed. They **loop** until the\n",
    "input is acceptable. This single pattern prevents a huge class of bugs and attacks."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "386cb502",
   "metadata": {},
   "outputs": [],
   "source": [
    "def get_valid_age():\n",
    "    while True:\n",
    "        text = input(\"Enter your age (0-120): \")\n",
    "        try:\n",
    "            age = int(text)\n",
    "        except ValueError:\n",
    "            print(\"Please type digits only.\")\n",
    "            continue\n",
    "        if 0 <= age <= 120:\n",
    "            return age          # only escapes the loop when valid\n",
    "        print(\"That age is out of range. Try again.\")\n",
    "\n",
    "age = get_valid_age()\n",
    "print(\"Validated age:\", age)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "234a8608",
   "metadata": {},
   "source": [
    "---\n",
    "## 🧪 LAB 2A — Number Guessing Game (that never crashes)\n",
    "Write a game that:\n",
    "1. Picks a secret number (use the code given)\n",
    "2. Repeatedly asks the user to guess\n",
    "3. Says \"too high\" / \"too low\" until correct\n",
    "4. **Validates** input — typing `abc` should NOT crash it\n",
    "\n",
    "Fill in the `TODO`s."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "b9bc86e2",
   "metadata": {},
   "outputs": [],
   "source": [
    "import random\n",
    "secret = random.randint(1, 20)\n",
    "print(\"I'm thinking of a number from 1 to 20.\")\n",
    "\n",
    "# TODO: loop until the user guesses correctly\n",
    "# - use try/except to handle non-numbers\n",
    "# - tell them too high / too low\n"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "f9358fe8",
   "metadata": {},
   "source": [
    "## 🧪 LAB 2B — Validator Toolbox\n",
    "Write **two functions**:\n",
    "- `is_valid_username(name)` → returns `True` if the name is 3–15 characters and\n",
    "  only letters/numbers (hint: `name.isalnum()`), else `False`\n",
    "- `get_valid_number(prompt)` → keeps asking until the user types a real number, then returns it\n",
    "\n",
    "Test them at the bottom."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "f3d02b2b",
   "metadata": {},
   "outputs": [],
   "source": [
    "# LAB 2B — your code here\n",
    "def is_valid_username(name):\n",
    "    # TODO\n",
    "    pass\n",
    "\n",
    "def get_valid_number(prompt):\n",
    "    # TODO\n",
    "    pass\n"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "d86e2a90",
   "metadata": {},
   "source": [
    "## 🧪 LAB 2C — To-Do List Manager\n",
    "Build a tiny menu program using a **list**:\n",
    "- `1` Add a task   `2` Show all tasks   `3` Quit\n",
    "- Use a `while True` loop and validate the menu choice\n",
    "\n",
    "This combines loops, lists, and input validation — everything from today!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "e9ce831c",
   "metadata": {},
   "outputs": [],
   "source": [
    "# LAB 2C — your code here\n",
    "tasks = []\n",
    "# TODO: menu loop\n"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "b5910c71",
   "metadata": {},
   "source": [
    "## 🏁 CHALLENGE — Make It Unbreakable\n",
    "Take any program from today and try every nasty input you can think of:\n",
    "empty Enter, letters, huge numbers, symbols. Add validation until **nothing** crashes it.\n",
    "Keep a \"bug log\" of what you found and fixed.\n",
    "\n",
    "---\n",
    "### ✅ Solutions (try first!)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "10661f28",
   "metadata": {},
   "outputs": [],
   "source": [
    "# --- LAB 2A solution ---\n",
    "import random\n",
    "secret = random.randint(1, 20)\n",
    "print(\"I'm thinking of a number from 1 to 20.\")\n",
    "\n",
    "while True:\n",
    "    guess_text = input(\"Your guess: \")\n",
    "    try:\n",
    "        guess = int(guess_text)\n",
    "    except ValueError:\n",
    "        print(\"Please enter a whole number.\")\n",
    "        continue\n",
    "    if guess == secret:\n",
    "        print(\"🎉 You got it!\")\n",
    "        break\n",
    "    elif guess < secret:\n",
    "        print(\"Too low.\")\n",
    "    else:\n",
    "        print(\"Too high.\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "7a3aa866",
   "metadata": {},
   "outputs": [],
   "source": [
    "# --- LAB 2B solution ---\n",
    "def is_valid_username(name):\n",
    "    return 3 <= len(name) <= 15 and name.isalnum()\n",
    "\n",
    "def get_valid_number(prompt):\n",
    "    while True:\n",
    "        try:\n",
    "            return float(input(prompt))\n",
    "        except ValueError:\n",
    "            print(\"Not a number — try again.\")\n",
    "\n",
    "print(is_valid_username(\"Sam99\"))    # True\n",
    "print(is_valid_username(\"a b\"))      # False\n",
    "print(is_valid_username(\"xy\"))       # False"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "df53561d",
   "metadata": {},
   "outputs": [],
   "source": [
    "# --- LAB 2C solution ---\n",
    "tasks = []\n",
    "while True:\n",
    "    print(\"\\n1) Add  2) Show  3) Quit\")\n",
    "    choice = input(\"Choose: \")\n",
    "    if choice == \"1\":\n",
    "        tasks.append(input(\"New task: \"))\n",
    "        print(\"Added!\")\n",
    "    elif choice == \"2\":\n",
    "        if not tasks:\n",
    "            print(\"(no tasks yet)\")\n",
    "        for i, t in enumerate(tasks, start=1):\n",
    "            print(i, \"-\", t)\n",
    "    elif choice == \"3\":\n",
    "        print(\"Bye!\")\n",
    "        break\n",
    "    else:\n",
    "        print(\"Pick 1, 2, or 3.\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "760cc38e",
   "metadata": {},
   "source": [
    "### 📝 Day 2 recap\n",
    "- `for` / `while` loops repeat work; lists & dicts store collections\n",
    "- functions make code reusable and easier to secure\n",
    "- 🔐 `try / except` + validation loops = programs that **fail gracefully**\n",
    "  instead of crashing. Tomorrow: protecting *data* — passwords, hashing, and secrets."
   ]
  }
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