day1_variable.ipynb

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 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Variables in Python"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Variable is just like a symbol that represents certain objects in Python. We use a variable to store a value so that we can use it in our program. Imagine you want to calculate the summation of two numbers in your mind, say 10 and 20. If you want the computer to do it for you, you can first use two variables to store these numbers like this\n",
    "```\n",
    "a = 10\n",
    "b = 20\n",
    "```\n",
    "Then, the computer will know variable `a` holds a number 10 and variable `b` holds a number 20. In this case, `a` and `b` look like containers that we put can numbers in it. \n",
    "\n",
    "After that, let the computer do the math for us! \n",
    "```\n",
    "a + b\n",
    "```\n",
    "If we run the above line of code, we should see the summation of 10 and 20 pop out in the window 🤩"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "a = 10\n",
    "b = 20"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "10"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
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   "source": [
    "a"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "30"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
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   "source": [
    "a + b"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [],
   "source": [
    "a = 120\n",
    "b = 30"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "120"
      ]
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     "execution_count": 5,
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     "output_type": "execute_result"
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   "source": [
    "a"
   ]
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  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "150"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a + b "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Naming of Variables\n",
    "\n",
    "We already know that a variable can represent or hold a number. A question is how should we pick the name of a variable? Usually we want the name to be something that we can easily remember and meaningful to us. For example, if we want to calculate the number of dollars that you have spent for buying a lego and a toy car, we can use a variable called `lego_cost` to represent the cost of the lego and `car_cost` to represent the cost of the car like the following\n",
    "```\n",
    "lego_cost = 38.5\n",
    "car_cost = 25.5\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [],
   "source": [
    "lego_cost = 38.5\n",
    "car_cost = 25.5"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "38.5"
      ]
     },
     "execution_count": 8,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "lego_cost"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "64.0"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "lego_cost + car_cost"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We can acutally use almost every possible symbol as a variable name. But the variable name can not start with a number or certain special characters like `=` or `+`. More importantly, we prefer variable names that can be easily remembered not like the example below where the variable name doesn't seem meaningful."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [],
   "source": [
    "ui97yki9 = 123"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "123"
      ]
     },
     "execution_count": 11,
     "metadata": {},
     "output_type": "execute_result"
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   "source": [
    "ui97yki9"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Use Variable to Hold String\n",
    "\n",
    "Other than holding a number, a variable can also hold a string or even a sentence! For example, we can define \n",
    "```\n",
    "my_greeting = \"Hello everyone, nice to meet you!\"\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [],
   "source": [
    "my_greeting = \"Hello everyone, nice to meet you!\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'Hello everyone, nice to meet you!'"
      ]
     },
     "execution_count": 18,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "my_greeting"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {},
   "outputs": [],
   "source": [
    "my_friend_response = \"Nice to meet you too!\""
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'Hello everyone, nice to meet you!Nice to meet you too!'"
      ]
     },
     "execution_count": 20,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "my_greeting + my_friend_response"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "This looks awesome! The computer just created a new sentence that includes both my greeting and my friend's response.👸 \n",
    "\n",
    "We can make the outcome look even nicer by adding a blank space between the two sentences."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'Hello everyone, nice to meet you! Nice to meet you too!'"
      ]
     },
     "execution_count": 22,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "my_greeting + \" \" + my_friend_response"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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