Ruby Monstas

Variables

IRB: As soon as you hit Enter and the Ruby command has finished executing, the result is forgotten

We should be able to use the result of one line in the next

Enter variables!

The drawer metaphor

You can think of variables like drawers in an apothecary

The drawers each have a label on them and they contain a specific thing at any time (or nothing)

my_string = "Hello world"

a_number = 5 + 2

my_string = "Hello world"

a_number = 5 + 2

Note:

is called the assignment operator

Note:

differs from how it's used in mathematics

Note: We're defining the variable and initializing it with a value

Note: Syntax is

variable_name = expression

"Hello world"

a_number.odd?

my_string.include?("Hello")

8 * 6

(a_number / 5.0) + 42

An expression is any piece of Ruby code that returns a value

Any expression can be assigned to a variable!

b_number = (a_number / 5.0) + 42

You can give existing variables a new value by reassigning

a_number = 5 + 2
a_number = 42

Note: Note syntax is the same as for assignment

Note: The old value of the variable is lost by doing this

You can also use the variable in an expression when reassigning it

a_number = 5 + 2
a_number = a_number + 3

Note: Here's where it definitely stops making sense mathematically ;-)

A variable always has a specific type

For example String or Integer

Whenever Ruby executes a method on a variable, it first checks the type!

a_number = 5 + 2
a_number.length

NoMethodError (undefined method `length' for 7:Integer)

Which of these are good variable names?

mynewvariable
user_name
date_of_birth
5_things
AnotherVariableName
list_of_favourite_drinks

These characters are allowed:

Variable names can't contain spaces (use

instead)

Variable names can't start with a digit

What questions do you have?