{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# If statements"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## What we know so far\n",
    "\n",
    "- Expressions\n",
    "- Variables\n",
    "- Print Statements\n",
    "- Types\n",
    "\n",
    "We can already do a lot with what we know so far. But what if we wanted to make something that is adaptable to specific situations?"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Making Decisions: if, elif, and else\n",
    "\n",
    "- How do we compute absolute values?\n",
    "\n",
    "**if** the value is *negative*, negate it\n",
    "\n",
    "**Otherwise** (else), use the original value"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "x = -10\n",
    "\n",
    "# calculate absolute value of x\n",
    "\n",
    "if x < 0:\n",
    "    result = -x\n",
    "else:\n",
    "    result = x\n",
    "\n",
    "print(x)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Try editing the above code to see if it works for any number! Here are some other ways of writing the same if statement"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "x = -10\n",
    "\n",
    "if x < 0:\n",
    "    print(-x)\n",
    "else:\n",
    "    print(x)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "What are some important components of the above if statements?\n",
    "\n",
    "* `val < 0`: This is called a *condition* and must be a boolean expression.\n",
    "* `result = -x` or `print(-val)`: These lines of code are only run *if* the conditon is true. They must be indented from the if statement.\n",
    "* `else`: Code to run if the condition is False. This is not required."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Multiple if statements can be used inside each other. These are called *nested if statements*"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "x = 0\n",
    "\n",
    "# calculate absolute value of x\n",
    "if x < 0:\n",
    "    print(\"x is negative\")\n",
    "    result = -x\n",
    "else:\n",
    "    if x == 0:\n",
    "        print(\"x is zero\")\n",
    "        result = 0\n",
    "    else:\n",
    "        print(\"x is positive\")\n",
    "        result = x\n",
    "\n",
    "print(x)\n",
    "print(result)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "However, nested if statements can be unwieldy especially when you have a lot of conditions. In these cases, you can use *elif* to specify more conditions besides the initial *if*."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "x = 0\n",
    "\n",
    "# calculate absolute value of val\n",
    "if x < 0:\n",
    "    print(\"x is negative\")\n",
    "    result = -x\n",
    "elif x == 0:\n",
    "    print(\"x is zero\")\n",
    "    result = 0\n",
    "else:\n",
    "    print(\"x is positive\")\n",
    "    result = x\n",
    "\n",
    "print(x)\n",
    "print(result)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Note that all of the `elif`s and `else` should follow the same indentation rules as the first `if`."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## More Examples"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Version 1\n",
    "\n",
    "height = 72\n",
    "if height > 100:\n",
    "    print(\"space\")\n",
    "else:\n",
    "    if height > 50:\n",
    "        print(\"mesosphere\")\n",
    "    else:\n",
    "        if height > 20:\n",
    "            print(\"stratosphere\")\n",
    "        else:\n",
    "            print(\"troposphere\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Version 2\n",
    "\n",
    "if height > 50:\n",
    "    if height > 100:\n",
    "        print(\"space\")\n",
    "    else:\n",
    "        print(\"mesosphere\")\n",
    "else:\n",
    "    if height > 20:\n",
    "        print(\"stratosphere\")\n",
    "    else:\n",
    "        print(\"troposphere\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Version 3 (Best)\n",
    "\n",
    "if height > 100:\n",
    "    print(\"space\")\n",
    "elif height > 50:\n",
    "    print(\"mesosphere\")\n",
    "elif height > 20:\n",
    "    print(\"stratosphere\")\n",
    "else:\n",
    "    print(\"troposphere\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Broken Version 3\n",
    "\n",
    "if height > 20:\n",
    "    print(\"stratosphere\")\n",
    "elif height > 50:\n",
    "    print(\"mesosphere\")\n",
    "elif height > 100:\n",
    "    print(\"space\")\n",
    "else:\n",
    "    print(\"troposphere\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Why does `height = 72` give different results?\n",
    "\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Incomplete Version 3\n",
    "\n",
    "if height > 20:\n",
    "    print(\"stratosphere\")\n",
    "elif height > 50:\n",
    "    print(\"mesosphere\")\n",
    "elif height > 100:\n",
    "    print(\"space\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "In this case it is possible that nothing is printed at all, when?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "if height > 100:\n",
    "    print(\"space\")\n",
    "if height > 50:\n",
    "    print(\"mesosphere\")\n",
    "if height > 20:\n",
    "    print(\"stratosphere\")\n",
    "else:\n",
    "    print(\"troposphere\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now what happens when `height` is 72? Or when `height` is 101?"
   ]
  }
 ],
 "metadata": {
  "kernelspec": {
   "display_name": ".venv",
   "language": "python",
   "name": "python3"
  },
  "language_info": {
   "codemirror_mode": {
    "name": "ipython",
    "version": 3
   },
   "file_extension": ".py",
   "mimetype": "text/x-python",
   "name": "python",
   "nbconvert_exporter": "python",
   "pygments_lexer": "ipython3",
   "version": "3.13.2"
  }
 },
 "nbformat": 4,
 "nbformat_minor": 2
}