--- marp: true title: 29 Jan 2021 theme: default paginate: true --- # CS 199 EMP ### Hosted by Jackie Chan and Akhila Ashokan **Topics:** Variables/Datatypes, Operations on Variables, and Conditional Statements/Expressions --- # Course Details Every Tuesday and Friday, there are two sessions that cover the same topic. - Session 1 @ 6AM on Tuesdays and Fridays w/ Akhila. - Session 2 @ 2PM on Tuesdays and 4PM on Fridays w/ Jackie. --- # Goals of the Course - Provide extra help and assistance to be successful in the course through practice problems. - Provide a safe environment to work on problems with others. Coding can be a very solitary activity, but not here. --- # Today's Learning Objectives Review briefly and practice: - Variables and datatypes - Operations on variables - Conditional expressions and statements Write code on the homepage or any playground on the site! https://cs125.cs.illinois.edu/ Slides are on the course site! https://cs199emp.netlify.app/ --- # What are variables? Variables are buckets that store data. Variable declarations looks like this: ```java ; // Initializing = ; // Assigning // Is equivalant to: = ; // Initializing and assigning ``` Here are some examples of variable declarations. ```java int myAge = 23; // is int (integer) double pi = 3.14; // is double (decimal) boolean programmingIsAwesome; programmingIsAwesome = true; // is boolean (true/false) char bestLetter = 'J'; // is char (a letter) ``` Questions before practice? --- # Practice with variables! (5 minutes) 1. Declare a variable called `firstLetter` with the first *letter* of your name. 2. Declare a variable `hadGoodSleep` that is `true` if you had good sleep, and `false` otherwise. 3. Declare a variable `minimumGPA` that is the minimum GPA for your program. 4. Declare a variable `mealsPerDay` with the number of meals you eat per day. Hint: You'll need to use `int`, `double`, `boolean`, and `char` only once in some order. --- # What can you do with variables? (Operations) For integers `int` and decimals `double`: - Add, subtract, multiply, divide (`+`, `-`, `*`, `/`). - Add, subtract, multiply, divide and assign (`+=`, `-=`, `*=`, `/=`) - Increment, i.e. add one, or decrement, i.e. subtract one (`++`, `--`). For booleans `bool`: - Negation, pronounced not in code. ```java boolean havingAGoodTime = true; boolean notHavingAGoodTime = !havingAGoodTime; // Not having a good time. ``` There are more with `String` too, but this is what we'll deal with. Questions before practice? --- # Practice with operations! (10 minutes) Tracking the number of people in Zoom. 1. Declare a variable `peopleInZoom` that is equal to the number of people in this Zoom call. 2. On the next line, increment `peopleInZoom` by one using `++`. 3. On the next line, add `7` to the variable `peopleInZoom` using `+=`. Negation practice. 1. Declare a boolean called `drankWater` if you have drank water today. 2. Reassign `drankWater` with the opposite value of `drankWater` using `!`. --- # What are conditional expressions and statements? Let's start off with expressions, conditional expressions are like questions that Java will evaluate and return `true` or `false`. - For `==` are the things on the left and right equal? - For `>` (`>=`) is the left value greater than the right value? Same goes with `<` and `<=` in the reverse. Conditional expressions go into conditional statements (otherwise known as if statements). We'll consider an example on the next page. --- Consider below. ```java double mealCost = 3.75 + 8.66; // Another example of an operation. mealCost *= 1.08; // Using the *= to multiple, and then assign back to mealCost. boolean mealIsExpensive = mealCost > 10.0; // Is this an expression or statement? if (mealIsExpensive) { // Is this an expression or statement? System.out.println("I'll put that on my business card!"); } // The above is the same as. if (mealCost > 10.0) { System.out.println("I'll put that on my business card!"); } ``` --- # Practice with conditional expressions and statements! (10 minutes) 1. Declare a variable `myAge` that contains your age. 2. Declare a variable called `canBuyAlcohol` that is true when `myAge` is greater or equal to `21` and false otherwise. 3. Write a conditional statement that prints "Get out of my store!" if `canBuyAlcohol` is false. Reminder that `!` is the negation operator. 4. Add an else statement to the if statement that prints "What can I help you with?". When will this print? --- # Reminder If-else statements look like. ```java if () { ```; } else { ; } ``` --- # Final, final questions about today's content? Anything! ```java if (!questions) { System.out.println("Have an awesome day!"); System.out.println("Be sure to mark attendance if that matters, " + "leave some feedback!"); } ``` Attendance and feedback links are found on the course site. https://cs199emp.netlify.app/ --- # Solutions Section --- # Practice with variables! (Solution) ```java char firstLetter = 'J'; // Note the single quotation. boolean hadGoodSleep = true; // Note that true and false are lowercased! double minimumGPA = 3.0; int mealsPerDay = 3; // Okay, maybe more than that. ``` --- # Practice with operations! (Solution) Tracking the number of people in Zoom. ```java int peopleInZoom = 13; peopleInZoom++; peopleInZoom += 7; // Notice that I don't need int here again. ``` Negation practice. ```java boolean drankWater = true; drankWater = !drankWater; // drankWater is now false. ``` Questions? --- # Practice with conditional expressions and statements! (Solution) ```java int myAge = 23; boolean canBuyAlcohol = myAge >= 21; if (!canBuyAlcohol) { // "If cannot buy alcohol." System.out.println("Get out of my store!"); } else { System.out.println("What can I help you with?"); } ``` ```