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message "A variable is a way to name a piece of data so we can do things with
it. It can hold all kinds of things - words, numbers, the result of a function,
and even a function itself."

goals do
  goal "Understand what a variable is for"
  goal "Store data in variables"
  goal "Replace data in an existing variable"

step do
  message "Start up irb on the Virtual Machine."
  console "irb"

step do
  irb "my_variable = 5"
  message "This creates a new variable called `my_variable` and stores the value 5 in it."
  message "Let's confirm that. To see what value a variable holds, type its name."
    irb "my_variable"
    result "5"

  irb "another_variable = \"hi\""

  message "This creates another variable and stores the value \"hi\" in it."


step do
  irb "my_variable = 10"
  message "`my_variable` has a new value."
  irb "my_variable"
  result "10"

step do
  irb <<-IRB
    apples = 5
    bananas = 10 + 5
    fruits = 2 + apples + bananas
    bananas = fruits - apples
  message "Variables are assigned a value using a single equals sign (=)."
  message "The right side of the equals sign is evaluated, and the result is
    assigned to the variable named on the left side of the equals."

step do
   message "You've created a lot of variables. Let's see the list."
   irb "local_variables"
   result "[:bananas, :fruits, :apples, :another_variable, :my_variable]"
   message "Here Ruby gives you a list of variables you've defined in irb so
     far. This might be useful for when you want to see what variable names are
     already in use."
step do
  message <<-CONTENT
  The opposite of a variable is `constant` - a value that doesn't change.
  Numbers, strings, nil, true, and false are constants.
  Check out what happens if you assign a value to a constant."
  irb <<-IRB
    true == false
    1 == 1
    "a" == 1
  message "(Notice in the last example we put the a in quotation marks to make it a string.)"

step do
  message "There are some rules about what you can name a variable."
	message <<-VARIABLE_NAMES
Try making variables with the following kinds of names in irb:

* all letters (like 'folders')

* all numbers (like '2000')

* an underscore (like 'first_name')

* a dash (like 'last-name')

* a number anywhere (like 'y2k')

* a number at the start (like '101dalmations')

* a number at the end (like 'starwars2')

Which worked? Which didn't?

step do
  message "Variables can hold the result of a function."
  irb 'shouting = "hey, you!".upcase'

explanation do
  message "Variables allow you to store data so you can refer to it by name
    later. The data you store in variables will persist as long as your program
    keeps running and vanish when it stops."

next_step "datatypes"