{ "cells": [ { "cell_type": "markdown", "id": "fb312eb6", "metadata": { "slideshow": { "slide_type": "slide" } }, "source": [ "# String Comparison, Chained Conditionals, and Logical Operators\n", "#### CS 65: Introduction to Computer Science I" ] }, { "cell_type": "markdown", "id": "e6535225", "metadata": { "slideshow": { "slide_type": "slide" } }, "source": [ "## Conditionals Review\n", "\n", "So far, we've seen _conditional statements_" ] }, { "cell_type": "code", "execution_count": 1, "id": "da7d98e0", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "What is your age? 67\n", "Applying 10% senior discount\n", "Your total bill is 32.067\n" ] } ], "source": [ "total_bill = 35.63\n", "age = float(input(\"What is your age? \"))\n", "\n", "if age > 65:\n", " print(\"Applying 10% senior discount\")\n", " total_bill = total_bill * 0.9\n", " #any indented code is only runs\n", " #when the condition is True\n", " \n", "#un-indented code runs no matter what\n", "print(\"Your total bill is\", total_bill)" ] }, { "cell_type": "markdown", "id": "f5c3fbd6", "metadata": {}, "source": [ "conditional statements with two alternatives" ] }, { "cell_type": "code", "execution_count": 2, "id": "32936d95", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Enter your height in inches: 61\n", "You are tall enough for this ride.\n" ] } ], "source": [ "height = int(input(\"Enter your height in inches: \"))\n", "\n", "if height < 60:\n", " print(\"You are not tall enough for this ride.\")\n", "else:\n", " print(\"You are tall enough for this ride.\")" ] }, { "cell_type": "markdown", "id": "624b5abf", "metadata": {}, "source": [ "and in the lab, we saw _nested_ conditional statements" ] }, { "cell_type": "code", "execution_count": 3, "id": "72772ad6", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Enter a number: 9\n", "9 is odd and divisble by 3\n" ] } ], "source": [ "num = int(input(\"Enter a number: \"))\n", "\n", "#this code checks if a number is divisible by both 2 and 3\n", "if num % 2 == 0:\n", " print(num,\"is even\")\n", "else:\n", " if num % 3 == 0:\n", " print(num,\"is odd and divisble by 3\")\n", " else:\n", " print(num,\"is odd and not divisible by 3\")" ] }, { "cell_type": "markdown", "id": "89a5826a", "metadata": { "slideshow": { "slide_type": "slide" } }, "source": [ "## Group Exercise: Comparing Strings\n", "\n", "Type the following program into Thonny, and run it several times. What does it do?" ] }, { "cell_type": "code", "execution_count": 10, "id": "c0a7abcb", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Enter a name: Eric\n", "Enter another name: Manley\n", "Eric is first\n" ] } ], "source": [ "name1 = input(\"Enter a name: \")\n", "name2 = input(\"Enter another name: \")\n", "\n", "if name1 < name2:\n", " print(name1,\"is first\")\n", "else:\n", " print(name2,\"is first\")" ] }, { "cell_type": "markdown", "id": "0fecf3dd", "metadata": {}, "source": [ "Is string comparison in Python case-sensitive? E.g., is `\"Eric\"` the same as `\"eric\"`? How could we test it?" ] }, { "cell_type": "code", "execution_count": null, "id": "38681114", "metadata": {}, "outputs": [], "source": [] }, { "cell_type": "markdown", "id": "f1069ee6", "metadata": { "slideshow": { "slide_type": "slide" } }, "source": [ "## Character representation\n", "\n", "Every text character is represented by a numerical code in your computer's memory. \n", "\n", "They came up with in the 1960's as part of the ASCII standard (https://en.wikipedia.org/wiki/ASCII)\n", "\n", "Here's some examples\n", "\n", "\n", "\n", " \n", " \n", "
\n", " \n", " \n", " \n", " \n", " \n", " \n", " \n", "
code character
33 !
34 \"
35 #
36 $
37 %
\n", " 		\n", " \n", " \n", " \n", " \n", " \n", " \n", " \n", "
code character
65 A
66 B
67 C
68 D
69 E
\n", " 		\n", " \n", " \n", " \n", " \n", " \n", " \n", " \n", "
code character
97 a
98 b
99 c
100 d
101 e
\n", " \n", "
\n", " \n", "You can use the built-in `ord()` function to look up the code for any given character. Use `chr()` to do the opposite." ] }, { "cell_type": "code", "execution_count": 11, "id": "a28db44b", "metadata": {}, "outputs": [ { "data": { "text/plain": [ "65" ] }, "execution_count": 11, "metadata": {}, "output_type": "execute_result" } ], "source": [ "ord(\"A\")" ] }, { "cell_type": "code", "execution_count": 14, "id": "f6a45e70", "metadata": {}, "outputs": [ { "data": { "text/plain": [ "'A'" ] }, "execution_count": 14, "metadata": {}, "output_type": "execute_result" } ], "source": [ "chr(65)" ] }, { "cell_type": "markdown", "id": "b8463c9e", "metadata": { "slideshow": { "slide_type": "slide" } }, "source": [ "## Other conditional statement options\n", "\n", "There are also __chained conditional statements__ when you have more than two choices\n", "\n", "`elif` a new keyword meaning \"else if\" which allows you to add as many more options to a conditional statement as you want." ] }, { "cell_type": "code", "execution_count": 4, "id": "1636b35c", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "What's the temperature? 40\n", "Let's put on jackets and go hiking.\n" ] } ], "source": [ "temp = float(input(\"What's the temperature? \"))\n", "\n", "if temp >= 70:\n", " print(\"Let's go hiking.\")\n", "elif temp >= 30:\n", " print(\"Let's put on jackets and go hiking.\")\n", "elif temp >= 10:\n", " print(\"Let's go skiing.\")\n", "else:\n", " print(\"It's too cold. Let's stay in and code.\")" ] }, { "cell_type": "markdown", "id": "b2b0c20b", "metadata": {}, "source": [ "Note:\n", "* `else` part is still optional but gives you the opportunity for \"default\" behavior\n", "* at most one block in a `if-elif-else statement` will run" ] }, { "cell_type": "markdown", "id": "39991c37", "metadata": { "slideshow": { "slide_type": "subslide" } }, "source": [ "## a common chained-conditional logic error" ] }, { "cell_type": "code", "execution_count": 5, "id": "28065030", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "What's the temperature? 80\n", "Let's go skiing.\n" ] } ], "source": [ "temp = float(input(\"What's the temperature? \"))\n", "\n", "if temp >= 10:\n", " print(\"Let's go skiing.\")\n", "elif temp >= 30:\n", " print(\"Let's put on jackets and go hiking.\")\n", "elif temp >= 70:\n", " print(\"Let's go hiking.\")\n", "else:\n", " print(\"It's too cold. Let's stay in and code.\")" ] }, { "cell_type": "markdown", "id": "1b94ca3a", "metadata": {}, "source": [ "Make sure to put the conditions in the order you want to check them - the first one to evalute to `True` will be the one that runs." ] }, { "cell_type": "markdown", "id": "87b464e7", "metadata": { "slideshow": { "slide_type": "slide" } }, "source": [ "## Logical Operators\n", "\n", "__Logical operators__ are operators that take Booleans as operands: `and`, `or`, `not`" ] }, { "cell_type": "code", "execution_count": 6, "id": "0479f27a", "metadata": {}, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "What's the temperature? 60\n", "Is it raining? yes\n", "Grab your coat.\n" ] } ], "source": [ "temp = float(input(\"What's the temperature? \"))\n", "raining = input(\"Is it raining? \")\n", "\n", "if temp < 50 or raining == 'yes':\n", " print(\"Grab your coat.\")\n", "\n", "if not (raining == 'yes') and temp > 70:\n", " print(\"Grab your mitt.\")" ] }, { "cell_type": "code", "execution_count": null, "id": "9268fcdd", "metadata": { "slideshow": { "slide_type": "slide" } }, "outputs": [], "source": [ "a = 2\n", "b = 4\n", "c = 6" ] }, { "cell_type": "markdown", "id": "6240fbac", "metadata": {}, "source": [ "See if you can work out the values below before the answer is revealed" ] }, { "cell_type": "code", "execution_count": null, "id": "f43a0a30", "metadata": { "slideshow": { "slide_type": "-" } }, "outputs": [], "source": [ "a == 4 or b > 2" ] }, { "cell_type": "code", "execution_count": null, "id": "cb0246ae", "metadata": { "slideshow": { "slide_type": "-" } }, "outputs": [], "source": [ "6 <= c and a > 3" ] }, { "cell_type": "code", "execution_count": null, "id": "35b6a0cc", "metadata": { "slideshow": { "slide_type": "-" } }, "outputs": [], "source": [ "1 != b and c != 3" ] }, { "cell_type": "code", "execution_count": null, "id": "f4e30662", "metadata": { "slideshow": { "slide_type": "-" } }, "outputs": [], "source": [ "a >= -1 or a <= b" ] }, { "cell_type": "code", "execution_count": null, "id": "e8fd899b", "metadata": { "slideshow": { "slide_type": "-" } }, "outputs": [], "source": [ "not a > 2" ] }, { "cell_type": "markdown", "id": "348bf1bd", "metadata": { "slideshow": { "slide_type": "slide" } }, "source": [ "Logical operators are pretty intuitive because we use them in our natural language, but they can sometimes be tricky when you get complex expressions." ] }, { "cell_type": "code", "execution_count": null, "id": "2e6d6d89", "metadata": {}, "outputs": [], "source": [ "a = 2\n", "b = 4\n", "c = 6\n", "result = a == 2 or b != 2 and c != 6 or a == b + c\n", "print(result)" ] }, { "cell_type": "markdown", "id": "b8b28570", "metadata": { "slideshow": { "slide_type": "fragment" } }, "source": [ "Rule of thumb: Always use parentheses when you have more than one logical operator" ] } ], "metadata": { "celltoolbar": "Slideshow", "kernelspec": { "display_name": "Python 3", "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": "3.8.8" } }, "nbformat": 4, "nbformat_minor": 5 }