rubyNotes.md

Ruby

• an object orientated language

Comments

• start with octothorps

Output

• keywords
  • puts will move cursor to the next line
  • print will keep the cursor on the same line
• in output statements, you can use #{variable_name} to input variables
• \ (backslash) is used as an escape character
  • \n new line character
  • \t new tab character
  • \r carriage return
  • \v new vertical tab
• using the triple double quotes, the string can span several lines

Input

• use "print" to keep it on the same line
• "gets.chomp" for strings
  • use ".to_i" to convert to int
  • use ".to_f" to convert to float
• ARGV (argument variable)
  • used when you want the user to input information before the script runs

Operators

• math operators
  • /
  • %
  • <
  • <=

  • =

• boolean operators
  • && (and)
  • || (or)
  • ! (not)
  • != (not equal)
  • == (equal)

  • = (greater-than-equal)

  • <= (lesser-than-equal)
  • true
  • false

Variables

• assign them using the = sign
• ||= for default assigning
• argument variable is assigned when you run it
• arrays
  • are set in square brackets ( [] )
  • .push to push to the end
  • use .split(' ') to split strings
• hashes
  • are set in curly brackets ( { } )
  • assigned values using "=>"
  • anything can be used as a key
  • .delete to delete keys and values associated with them

Reading and writing files

• txt = open(filename)
  • close() to close the file
• readline() reads one line
• truncate() empties the file
• write('stuff') writes "stuff" to the file

Functions

• use def and end to signify start and end
• *args is like ARGV but for functions
• can return a value using "return"

  def print_two(arg1, arg2)
    puts "arg1: #{arg1}, arg2: #{arg2}"
    end

  print_two("Jenny", "Chen")

Modules

• a collection of methods and constants
• can import to use methods and stuff
• can access variables using ::
• "require"

Classes

• keyword class

• instantiate new objects using .new()

• use @ to distinguish variables inside the class

• use $ to distinguish variables from outside the class

• inheritance

• mixins

  • can use modules in classes as well
  • "include"

  class mammal
    def breathe
      puts "Inhale and exhale."
    end
  end
  
  # Use the less than sign to signal inheritance
  class cat < mammal
    def speak
      puts "Meow"
    end
  end
  
  dave = cat.new()
  dave.speak()
  dave.breathe()

Loops

• if statements

if people < cats
  puts "Too many cats! The world is doomed!"
elsif people > cats
  puts "Too many people! The world is doomed!"
else
  puts "Purrfect!"
end

• for loops
  • use (firstNumber .. secondNumber) to show ranges

fruits = ["apples", "oranges", "pears", "apricots"]

for fruit in fruits
  puts "I love #{fruit}"
end

fruits.each do |fruit|
  puts "I love #{fruit}"
end

fruits.each {|fruit| puts "I love #{fruit}"}

• while loops

i = 0
numbers = []

while i < 6
  puts "i = #{i}"

  i += 1

  puts "i = #{i}"
end