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    "# Programming Techniques — Laboratory\n",
    "## Input, Type Conversion and Strings\n",
    "\n",
    "This laboratory follows the order used in class, but the exercises deliberately **combine several concepts**.\n",
    "\n",
    "### Topics\n",
    "- `input()`\n",
    "- type conversion with `int()`, `float()` and `str()`\n",
    "- `int()` with a **base** (binary, hexadecimal, ...)\n",
    "- common conversion errors\n",
    "- `len()` with strings\n",
    "- character indexes\n",
    "- slicing, including negative steps\n",
    "- escape sequences\n",
    "- functions vs. methods\n",
    "- string methods: `.lower()`, `.upper()`, `.replace()`\n",
    "- f-strings\n",
    "\n",
    "### Working style\n",
    "1. **Guided exercise** — follow the instructor hands-on.\n",
    "2. **Laboratory exercises** — work semi-independently; ask questions and discuss your choices.\n",
    "3. **Independent review** — more complete exercises for consolidation and homework.\n",
    "\n",
    "> In this notebook we use strings as sequences. We do **not** use lists or loops yet."
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    "---\n",
    "# Part A — Guided Exercise\n",
    "## 1. Conference registration receipt\n",
    "\n",
    "### Theory recall\n",
    "\n",
    "`input()` always returns a **string**:\n",
    "\n",
    "```python\n",
    "name = input(\"Participant name: \")\n",
    "```\n",
    "\n",
    "When a string represents a number, it can be converted:\n",
    "\n",
    "```python\n",
    "tickets = int(\"3\")       # 3\n",
    "price = float(\"12.50\")   # 12.5\n",
    "text = str(42)           # \"42\"\n",
    "```\n",
    "\n",
    "### `int()` and number bases\n",
    "\n",
    "`int()` can also interpret a string using a specified **base**:\n",
    "\n",
    "```python\n",
    "int(\"1010\", 2)     # 10   binary → integer\n",
    "int(\"1A\", 16)      # 26   hexadecimal → integer\n",
    "int(\"25\", 10)      # 25   decimal → integer\n",
    "```\n",
    "\n",
    "The second argument tells Python how to interpret the digits.\n",
    "\n",
    "Invalid digits for the selected base cause a `ValueError`:\n",
    "\n",
    "```python\n",
    "int(\"102\", 2)      # ValueError: 2 is not a binary digit\n",
    "int(\"1G\", 16)      # ValueError: G is not a hexadecimal digit\n",
    "int(\"3.14\")        # ValueError: not an integer representation\n",
    "```\n",
    "\n",
    "For decimal numbers with a fractional part, use `float()`:\n",
    "\n",
    "```python\n",
    "float(\"3.14\")      # 3.14\n",
    "```\n",
    "\n",
    "### Task\n",
    "\n",
    "Build a small registration receipt.\n",
    "\n",
    "Ask the user for:\n",
    "- participant name;\n",
    "- number of tickets;\n",
    "- price per ticket;\n",
    "- a short **binary registration code**.\n",
    "\n",
    "Then:\n",
    "1. convert the numeric inputs;\n",
    "2. convert the binary code to an integer using `int(..., 2)`;\n",
    "3. calculate the total cost;\n",
    "4. print a compact receipt using an **f-string**.\n",
    "\n",
    "Example:\n",
    "\n",
    "```text\n",
    "Participant name: Sofia\n",
    "Number of tickets: 3\n",
    "Price per ticket: 12.50\n",
    "Binary registration code: 10101\n",
    "\n",
    "Sofia bought 3 tickets.\n",
    "Total: €37.50\n",
    "Registration code: 21\n",
    "```"
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    "name = input(\"Participant name: \")\n",
    "\n",
    "# TODO: read the remaining values\n",
    "# TODO: convert them to the appropriate types\n",
    "# TODO: convert the binary registration code using int(binary_text, 2)\n",
    "# TODO: calculate the total\n",
    "# TODO: print the receipt with f-strings"
   ]
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    "### Quick discussion\n",
    "- What type does `input()` return?\n",
    "- Why do we need `int()` or `float()` before arithmetic?\n",
    "- What does the `2` mean in `int(binary_code, 2)`?\n",
    "- What would happen with `int(\"102\", 2)`?\n",
    "- What does `{total:.2f}` do inside the f-string?"
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