Variables

Let's dive in further.

One of the most fundamental concepts in programming is called a variable. Variables are what allow programmers like you to store information throughout their code. Here's what declaring (or setting the value of) a variable looks like in Kotlin:

var teamName = "SERT"

Now lets break this down. The var keyword (a specific word or command which tells the computer what you're doing) is used whenever you want to make a new variable that can change later. The teamName is just the name of the variable. The equal sign = means that we want to give the variable a value, and "SERT" is the value that we are assigning to the variable.

Now lets look at another example:

val teamNumber = 2521

There are a few differences in this example to explain. The most obvious one is that instead of var, our variable is declared with val. The difference between var and val is that a variable declared with var can be changed later, but a variable declared with val cannot. Trying to change a variable declared with val will result in errors when trying to run your program. Another difference is the type of value we assign the variable. In the previous example, we assigned a string to the variable, but here we assign a number. Note that there are no quotations around the number. Numbers do not need quotation marks.

Well, if a variable declared with var can change, how do we change it? Good question! To change the value of a variable, just do something like this:

var willChange = "I won't be set to this for long."
willChange = "I changed!"

This is called reassigning a variable. Note that you do not have to use the var keyword again, you must only use it when you first declare the variable. Also note that you cannot set a variable to a different type. For example, you cannot assign a variable that was originally storing a string to later be a number. You'll learn more about data types in the next lesson.

Your Turn

1. Open up src/main/kotlin/part1/Variables.kt.

2. In the main function, declare a new variable with var. It can store whatever whatever you want.

3. On the next line, put the name of your variable inside a println(...). Run the program. Were

   you surprised?

4. Next, reassign the variable to a different value, and then put it inside println(...) again.

   Run the program again.

5. Finally, change the var to val and try to run the program. Did it work?

That last instruction should have caused an error. It's impossible to reassign a variable declared with the val keyword. Variables are some of the most useful tools in any programming language, as they let us store and use data within a program, even if we don't exactly know what it will be. Next, we will discuss data types.