Variables are a way of assigning data to names in your programs. You can think of a variable as a box with a label on it: it stores something and has a name so that you know what’s inside. This is an imperfect metaphor as you’ll see by the end of this lesson, but it should help with understanding variables for now.
By the end of this lesson, you should be able to do the following:
/=assignment operators do.
This is how to create a variable in Ruby:
age = 18 #=> 18
You can also assign the result of an expression to a variable.
age = 18 + 5 #=> 23
Variable names are reusable, so you can assign a new value to a variable at any point in your program. Naturally, doing so will override the original value.
age = 18 age #=> 18 age = 33 age #=> 33
There will often be scenarios where you want to perform an operation on the original value of a variable and then reassign the result of that operation to the same variable.
age = 18 age #=> 18 age = age + 4 age #=> 22
Because this is a common scenario, Ruby provides a nice shorthand assignment operator for doing this:
age = 18 age += 4 #=> 22
There are similar assignment operators for all the common math operators:
age = 18 age -= 2 #=> 16 cash = 10 cash *= 2 #=> 20 temperature = 40 temperature /= 10 #=> 4
Ruby is a language that aims to be natural to read and easy to write. Remember this when you’re naming your variables. The name should, as clearly as possible, describe what the value of the variable represents.
Naming variables clearly will pay dividends when you review your code months after you’ve written it, when you can no longer remember what that variable was designed to store. From now on, when naming your variables, remember the following quote by John Woods:
Always code as if the person who ends up maintaining your code will be a violent psychopath who knows where you live.
The most basic thing you can do to write clean, maintainable code is to name your variables properly. So get into this habit early to avoid psychopath programmers coming after you.
Variable names should always be lowercase, and multiple words that make up a variable name should be split by an underscore. This is known as snake_case.
# bad a = 19 string = "John" # good age = 19 name = "John" can_swim = false
The information you name with a variable is stored in memory on your computer, so a variable is effectively a reference or a pointer to that address in memory. This is important to know as it can sometimes be the cause of unexpected behavior from your code.
Let’s look at an example of this unexpected behavior, with two variables:
desired_location, which is assigned to the string “Barcelona”, and
johns_location, which is assigned to the
desired_location variable. Both variables are pointing to where “Barcelona” is stored in memory.
desired_location = "Barcelona" johns_location = desired_location desired_location #=> "Barcelona" johns_location #=> "Barcelona"
Unexpected behavior happens if the string “Barcelona” that is stored in memory is modified. One way to modify a string is to use the
upcase! method, instead of the safe
upcase method. If the string is modified using
desired_location will also reflect that change:
johns_location.upcase! #=> "BARCELONA" desired_location #=> "BARCELONA" johns_location #=> "BARCELONA"
This example may be hard to completely understand at this point in the lesson. The important concept is that assigning variables to other variables can have unintended side effects. Just because you can do it, doesn’t mean you should. You will have the opportunity to revisit this example in one of the following assignments.
@@class_variablesare rarely needed and easily misused.
upcase!, as in the example above. If you come across anything quirky, Google it to find out why it happened.
This section contains helpful links to other content. It isn’t required, so consider it supplemental.
This section contains questions for you to check your understanding of this lesson. If you’re having trouble answering the questions below on your own, review the material above to find the answer.