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    "# Class Notes 30/09/2025 — While loops, For loops & Iterables\n",
    "## Try me\n",
    "[![Open In Colab](https://colab.research.google.com/assets/colab-badge.svg)](https://colab.research.google.com/github/ffraile/computer_science_tutorials/blob/main/source/Introduction/class%20notes/class_notes_30092025.ipynb)[![Binder](https://mybinder.org/badge_logo.svg)](https://mybinder.org/v2/gh/ffraile/computer_science_tutorials/main?labpath=source%2FIntroduction%2Fclass%20notes%2Fclass_notes_30092025.ipynb)\n",
    "\n",
    "## 2) `while` Loops\n",
    "\n",
    "**Definition:** Repeat a block **while** a condition remains `True`.\n",
    "**Syntax:**\n",
    "```python\n",
    "while condition:\n",
    "    # loop body\n",
    "    # executed while the condition is True\n",
    "    # condition is re-evaluated each iteration\n",
    "```\n",
    "**Important**\n",
    "- Ensure the loop **eventually stops** (update variables, read input, etc.).\n",
    "- Use `break` to exit early; `continue` to skip to next iteration.\n",
    "\n",
    "\n"
   ],
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    "# Example: echo until user types 'quit' (safe sentinel pattern)\n",
    "while True:\n",
    "    msg = input(\"Say something ('quit' to stop): \")\n",
    "    if msg.strip().lower() == \"quit\":\n",
    "        break                 # exit the loop\n",
    "    if not msg:               # empty input? skip\n",
    "        continue\n",
    "    print(\"You said:\", msg)\n",
    "print(\"Bye!\")"
   ],
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   "source": [
    "**`break` / `continue` demo**\n",
    "\n",
    "\n"
   ],
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    "x = 0\n",
    "y = 0\n",
    "while x < 5:\n",
    "    x += 1\n",
    "    if x % 2 == 0:        # even\n",
    "        print(x, \"is even\")\n",
    "        continue          # go to next iteration (skip y += x)\n",
    "    y += x                # odd: accumulate\n",
    "print(\"Sum of odd numbers 1..5 is\", y)"
   ],
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    "## 3) Iterables: Lists\n",
    "\n",
    "**Definition:** Ordered, indexable, mutable collection.\n",
    "**Create:** `lst = [a, b, c]` • Empty: `[]` • Length: `len(lst)`\n",
    "**Indexing:** `lst[i]` (0-based) • Negative index from end: `lst[-1]`\n",
    "\n",
    "**Common ops:** `append`, `pop`, `insert`, `remove`, `in`, `count`\n",
    "\n",
    "\n"
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    "row = [\"A\", \"B\", \"C\"]\n",
    "print(len(row), row[0], row[-1])  # 3 A C\n",
    "row.append(\"D\")\n",
    "print(row)   # [\"A\", \"B\", \"C\", D]"
   ],
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    "### 3.1 Slicing\n",
    "\n",
    "- **Syntax:** `seq[start:stop:step]` slices seq from start to stop with step (stop **excluded**)\n",
    "- Omitted parts default to start, step 1, or end of the sequence.\n",
    "- Use negative step to go backwards\n"
   ],
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    "s = [\"A\",\"B\",\"C\",\"D\",\"E\",\"F\"]\n",
    "print(s[1:4])     # ['B','C','D']\n",
    "print(s[:3])      # first three\n",
    "print(s[3:])      # from index 3 to end\n",
    "print(s[::2])     # every 2nd\n",
    "print(s[::-1])    # reversed copy"
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    "## 4) `for` Loops\n",
    "\n",
    "**Definition:** Iterate over the elements of an iterable.\n",
    "**Syntax:**\n",
    "```python\n",
    "for element in iterable:\n",
    "    # use element\n",
    "```\n",
    "**Tips**\n",
    "- Use `for name in names:` to get items; use `enumerate(iterable)` when you also need the index.\n",
    "- `continue` and `break` work as in `while` loops.\n",
    "\n",
    "### Grasping the concept: Iteration\n",
    "#### Real‑world example: corporate emails\n",
    "Let us write a hand-made email generator. Each student in the first row, given their full name, should write in the whiteboard an email with the following format:\n",
    "**Rule:** first initial + surname (lowercase, no spaces/hyphens) + `@stark_company.com`"
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    "\n",
    "names = [\"Tony Stark\", \"Bruce Banner\", \"Thor Odinson\"]\n",
    "for full in names:\n",
    "    print(full) #prints names in different lines\n",
    "\n",
    "for i, full in enumerate(names, start=1):\n",
    "    print(i, full)"
   ],
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    "### 4.1 Range\n",
    "The ```range``` function is a built-in function widely used in combination with for loops.\n",
    "- Use `range(n)` to loop a specific number of times.\n",
    "- Use `range(start,stop,step) as in slicing to generate a specific numeric sequence\n",
    "\n",
    "for i in range(5):\n"
   ],
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    "for i in range(5):\n",
    "    print(i)        # prints 0, 1, 2, 3, 4\n",
    "\n",
    "for i in range(1,7,2):\n",
    "    print(i)        # prints (1, 3, 5)"
   ],
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    "## 5) Quick Checks (self‑test)\n",
    "\n",
    "1) What does this print and **why**?\n",
    "```python\n",
    "x = 20\n",
    "if x < 20:\n",
    "    msg = \"A\"\n",
    "elif x <= 20:\n",
    "    msg = \"B\"\n",
    "else:\n",
    "    msg = \"C\"\n",
    "print(msg)\n",
    "```\n",
    "2) Write a loop that sums only the **even** numbers in `nums = [0,1,2,3,4,5]`.\n",
    "3) Slice `letters = list(\"ABCDEFG\")` to get `[\"C\",\"D\",\"E\"]`.\n",
    "4) Turn the rule “`age` between 18 and 64 inclusive” into a single boolean expression.\n",
    "5) Try writing the corporate email generator from the example above.\n",
    "\n",
    "\n"
   ],
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