Coding practice

Goal: Teaching ruby to newbies

We will build a self-checkout machine used in a supermarket together.

Here is basic ruby syntax useful to this task.

Define Class

class with no argument

class Item
  def initialize()
  end
end

create with 1 argument

class Item
  def initialize(name)
  end
end

Create object

item1 = Item.new()
item2 = Item.new("apple")

Include other file

require "./item" # read file item.rb under the current folder and insert it

instance variable (start with @)

class Item
  def initialize(name)
    @name = name
  end
  def print()
    puts @name
  end
end
Item.new("apple").print() #=> "apple"

instance method

declear method

class Item
  def initialize()
  end
  def price(quantity)
    10 * quantity # result of the last line returns automatically
  end
end

call method

price = Item.new().price(5) #=> 50

Condition

if statement

if (1 == 1)
  puts "case1"
elsif (2 == 2)
  puts "case2"
else
  puts "case3"
end

switch statement

case 1
when 1
  puts "1"
when 2
  puts "2"
end

String

create string

name = "apple"

append string

name = "apple"
puts name + "orange" #=> apple orange

combine strings

name = "apple"
puts "having #{name}" #=> having apple

Array

create empty array

array = []

add item to array

array = []
array << "mlik"

get item by index

array = ["apple", "orange"]
array[0] #=> "apple"

find index of item

array = ["apple", "orange"]
array.index("apple") #=> 0

loop through each item

array = ["apple", "orange"]
array.each do |item|
  puts item # execute this line for each item
end #=> "apple\norange"
array.each { |item| puts item } # same as above

map to create a new array with different value

array = [1,2,3]
array.map do |item|
  item * 3
end #=> [3,6,9]

Minitest

file name ends with "_test.rb"

basic format

require 'minitest/autorun'
describe "math" do            # 'describe' block wraps 'it' blocks
  it "can sum two numbers" do # 'it' block represents single test
    assert_equal(2, 1 + 1)    # assertion
  end
end

assetion

expected = true
actual = (1 + 1 == 2)
assert_equal(expected, actual)