Ruby/Language Basics/Variables
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Array elements automatically assigned to variables
x,y,z = [1,2,3] # Array elements automatically assigned to variables
Assign constant array value to three variables
a, b, *c = [12, 14, 178, 89, 90] puts a # => 12 puts b # => 14 puts c # => [178, 89, 90]
Assign values to more than one variable in one statement
array = [:red, :green, :blue] c, a, b = array puts a # => :green puts b # => :blue puts c # => :red
create a variable and compare it with a number.
# If the variable and number are equal, the code is executed. x = 256 if x == 256 puts "x equals 256" end # => x equals 256
Define a variable to hold an integer
x = 10
puts x
Doing a calculation
temperature = 36 puts "The temperature is " + String(temperature) + "." temperature = temperature + 5 puts "Now the temperature is " + String(temperature) + "."
Everything Is an Object
class MyClass def my_method end end a_class = MyClass an_object = MyClass.new a_method = an_object.my_method print 42.class, " " print a_class.class, " " print an_object.class, " " print a_method.class, " " print a_method.methods.class
Exchange three value with using new variables
a, b, c = :red, :green, :blue c, a, b = a, b, c puts a # => :green puts b # => :blue puts c # => :red
Exchange value with an extra variable
a, b = 1, 2 x = a a = b b = x
Exchanging Values Without Using Temporary Variables
a = 1 b = 2 a, b = b, a puts a # => 2 puts b # => 1
give a value a name by assigning it to a variable
hi = "Hello, Matz!" puts hi # => Hello, Matz!
Interpolation with two variables
n, animal = 2, "mice" "#{n+1} blind #{animal}" # => "3 blind mice"
Math calculation
1 + 2 # => 3: addition 1 * 2 # => 2: multiplication 1 + 2 == 3 # => true: == tests equality 2 ** 1024 # 2 to the power 1024: Ruby has arbitrary size ints
Objects Might Have Their Own Methods
class MyClass def speak puts "Ruby!" end end first_object = MyClass.new second_object = MyClass.new def first_object.sing puts "Give My Regards to Broadway" end first_object.speak second_object.speak first_object.sing second_object.sing
Prefix and variable type
$files # A global variable @data # An instance variable @@counter # A class variable empty? # A Boolean-valued method or predicate sort! # An in-place alternative to the regular sort method timeout= # A method invoked by assignment
Storing Data in Variables
# A standard variable starts with a lowercase letter, a to z, # or an underscore, _, followed by any number of name characters. # A name character is a lowercase letter, an uppercase letter, a digit, or # an underscore. temperature = 34 puts temperature
Swap the value of two variables
a, B = 1, 2 # Same as x = 1; y = 2 a, b = b, a # Swap the value of two variables
understand the difference between numbers and digits.
# 12 is a number, but "12" is a string of two digits. puts 12 + 12 puts "12" + "12" puts "12 + 12" # 24 # 1212 # 12 + 12
Variables allow you to write and use programs that work upon varying data.
x = 100 y = 10 puts x - y
variables can also be assigned the results of an expression
x = 50 y = x * 100 x += y puts x
variables can point to any kind of object
var = "just another " + "string" puts var var = 5 * (1+2) puts var
Variables in a Class
# The global variables are always preceded by the dollar sign ($). # using the class variable @@no_of_customers class Customer @@no_of_customers=0 end
==x, Same as/td>
x, y = 1, 2 # Same as x = 1; y = 2
