notebooks/variables.ipynb

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    "## Variables\n",
    "*Variables* are symbols for values in a program.\n",
    "Unlike variables in [mathematics](./algebra.ipynb/#Variables), which are symbols for one value, programs can change the values in variables. \n",
    "Initially variables have no value. \n",
    "Running this program gives an error."
   ]
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    {
     "ename": "NameError",
     "evalue": "name 'n' is not defined",
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      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mNameError\u001b[0m                                 Traceback (most recent call last)",
      "Cell \u001b[1;32mIn[5], line 1\u001b[0m\n\u001b[1;32m----> 1\u001b[0m \u001b[38;5;28mprint\u001b[39m(n)\n",
      "\u001b[1;31mNameError\u001b[0m: name 'n' is not defined"
     ]
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   "source": [
    "print(n)"
   ]
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   "source": [
    "This stores 5 in a variable named `x` and prints it out.\n",
    " `=` assigns 5 to `x`. "
   ]
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       "5"
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   "source": [
    "x = 5\n",
    "x"
   ]
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   "source": [
    "The variable can be shown like this, where `x` is a name for a place in which the value 5 is stored.\n",
    "![image](variable1.jpg)"
   ]
  },
  {
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   "source": [
    "A variable can be assigned a  value and then be assigned  another  value to replace it. \n",
    "This stores 5 in the variable `x`, prints it out, then stores 7 in `x` and prints it out."
   ]
  },
  {
   "cell_type": "code",
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   "source": [
    "x = 5\n",
    "print(\"first x is \", x)\n",
    "x = 7\n",
    "print(\"then x is \", x)"
   ]
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  {
   "cell_type": "markdown",
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   "source": [
    "This can be shown like this, where `x` stores the value 5, which is then replaced with the data 7.\n",
    "`→` means \"set to new value\".\n",
    "![variable2.jpg](variable2.jpg)\n",
    "A variable can also be assigned the value of another variable. \n",
    "This stores 5 in `x`, then assigns that value to the variable `y` and prints it out."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "9b438088",
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   "source": [
    "x = 5\n",
    "y = x\n",
    "print(\"x is \", x, \" and y is \", y)"
   ]
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  {
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   "id": "4cc447ea",
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   "source": [
    "![image](variable3.jpg)\n",
    "Variables can store many different types of data besides numbers.\n",
    "This stores a string in the variable `s` and prints it out."
   ]
  },
  {
   "cell_type": "code",
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   "id": "fc018780",
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   "source": [
    "s = \"Hello world\"\n",
    "print(\"s is \", s)"
   ]
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   "source": [
    "### A note on variable names\n",
    "Variable names start with a [*lowercase*](#glossary_lowercase) letter, `a` to `z`, or an [*uppercase*](#glossary_uppercase) letter, `A` to `Z`, or `_`. They can have a `_`, letter, or number inside but no other punctuation in them. They can not have a number at the beginning. "
   ]
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     "text": [
      "x is  2  x_y is  3 , _x is  4\n"
     ]
    }
   ],
   "source": [
    "x = 2\n",
    "x_y = 3\n",
    "_x = 4\n",
    "print(\"x is \", x, \" x_y is \", x_y, \", _x is \", _x)"
   ]
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   "source": [
    "Capital and small letters matter, the variable name must always look exactly the same everywhere."
   ]
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     "text": [
      "X is  5  x is  6\n"
     ]
    }
   ],
   "source": [
    "X = 5\n",
    "x = 6\n",
    "print(\"X is \", X, \" x is \", x)"
   ]
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   "cell_type": "markdown",
   "id": "d9f18433",
   "metadata": {},
   "source": [
    "Many Values to Multiple Variables\n",
    "Python allows you to assign values to multiple variables in one line:"
   ]
  },
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   "cell_type": "code",
   "execution_count": null,
   "id": "d253b2ca",
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   "source": [
    "x, y, z = \"Orange\", \"Banana\", \"Cherry\"\n",
    "print(x)\n",
    "print(y)\n",
    "print(z)"
   ]
  },
  {
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   "id": "2819c4d9",
   "metadata": {},
   "source": [
    "### Python Comments\n",
    "Comments can be used to explain Python code.\n",
    "\n",
    "Comments can be used to make the code more readable.\n",
    "Creating a Comment\n",
    "Comments starts with a `#`, and Python will ignore them:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "b73ce57f",
   "metadata": {},
   "outputs": [],
   "source": [
    "# This is a comment\n",
    "print(\"Hello, World!\")"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "70d8aaf3",
   "metadata": {},
   "source": [
    "Comments can be placed at the end of a line, and Python will ignore the rest of the line:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "21651c02",
   "metadata": {},
   "outputs": [],
   "source": [
    "print(\"Hello, World!\") # This is a comment"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "960f4df1",
   "metadata": {},
   "source": [
    "Multiline comments can be written using `#`."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "id": "e9d4e42e",
   "metadata": {},
   "outputs": [],
   "source": [
    "# written in\n",
    "# more than just one line\n",
    "print(\"Hello, World!\")"
   ]
  },
  {
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   "id": "037583ed",
   "metadata": {},
   "source": [
    "This is an alternate way to create a multiline comment. \n",
    "Python will ignore string literals that are not assigned to a variable, you can add a multiline string (triple quotes) in your code, and place your comment inside it:"
   ]
  },
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   "execution_count": 1,
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   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello, World!\n"
     ]
    }
   ],
   "source": [
    "\"\"\"\n",
    "This is a comment\n",
    "written in\n",
    "more than just one line\n",
    "\"\"\"\n",
    "print(\"Hello, World!\")"
   ]
  }
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