Update content of sections

Author: thanhluanuit

.gitignore

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+.idea/

README.md

@@ -1,96 +1,95 @@
-## Ruby Programming Tutorial 
+# Ruby Programming Tutorial 
 This tutorial help beginners easy to learn and approach Ruby step by step. Have solid basic to learn about Ruby on Rails.
 
-### What Will I Learn?
+## What Will I Learn?
 
 - Features, data types of Ruby.
 - Object-Oriented Programming in Ruby.
 - You’ll be able to code by Ruby programming language.
 
 
-### Table of contents
+## Table of contents
 
-- [Getting Started](/getting_started.md)
-    - Introduction
-    - Installation
-    - Running Ruby
-    - Official Documents
+### [Getting Started](/getting_started.md)
+- Introduction
+- Installation
+- Running Ruby
+- Official Documents
 
-- [Variables](/variables.md)
-    - What is a variable?
-    - Examples
+### [Variables](/variables.md)
+- What is a variable?
+- Examples
 
-- [Constants]()
-    - What is a constant?
-    - Example
-    - Best Pratise
-    
-- [Comments]()
-    - What is a comment?
-    - Single line comments
-    - Multiline comments
+### [Constants](/constants.md)
+- What is a constant?
+- Example
+- Tips
 
-- [Strings](/strings.md)
-    - What is a String in Ruby?
-    - Interpolation
-    - Indexing
-    - Common methods
+### [Comments](/comments.md)
+- What is a comment?
+- Single line comments
+- Multiline comments
 
-- [Numbers](/numbers.md)
-    - Integers
-    - Floats
-    - Operaters
-    - Convert numbers
-    
-- [True, False and Nil](/true_false_nil.md)
-    - true and false are the two Boolean values, and they represent truth and falsehood, yes and no, on and off.
-    - nil is a special value to indicate the absence of value.
+### [Strings](/strings.md)
+- What is a String in Ruby?
+- Interpolation
+- Indexing
+- Common methods
+
+### [Numbers](/numbers.md)
+- Integers
+- Floats
+- Operaters
+- Convert numbers
 
-- [Symbols](/symbols.md)
-    - What is a symbol in Ruby?
-    - Examples
-    - Common methods
+### [True, False and Nil](/true_false_nil.md)
+- true and false are the two Boolean values, and they represent truth and falsehood, yes and no, on and off.
+- nil is a special value to indicate the absence of value.
 
+### [Symbols](/symbols.md)
+- What is a symbol in Ruby?
+- Examples
+- Common methods
 
-- [Date & Time]()
+### Date & Time
 
-- [Arrays](/arrays.md)
-    - Create an Array
-    - Indexing
-    - Accessing elements
-    - Iteration 
-    - Common methods
+### [Arrays](/arrays.md)
+- Create an Array
+- Indexing
+- Accessing elements
+- Iteration 
+- Common methods
 
-- [Range]()
+### Range
 
-- [Hashes](/hashes.md)
-    - Create a Hash
-    - Accessing value by key
-    - Iteration
-    - Common Uses
+### [Hashes](/hashes.md)
+- Create a Hash
+- Accessing value by key
+- Iteration
+- Common Uses
 
-- [Control Flow](/conditional.md)
-    - if
-    - else
-    - elsif
-    - unless
-    - case
-    
-- [Blocks]()
-    - What is a blocks in Ruby?
-    - Examples
-    
-- [Methods]()
-    - Defining a method
-    - Default parameters in method
+### [Control Flow](/conditional.md)
+- if
+- else
+- elsif
+- unless
+- case
 
-- [Classes]()
-    - Defining a Class
-    - Constructor
-    - Accessing methods levels
-    - Accessing instance variables
+### [Blocks]
+- What is a blocks in Ruby?
+- Examples
 
-- [Module]()
-    - Mixin
-    - Module as Namespace
-    - Modules and Class Composition
+### Methods
+- Defining a method
+- Default parameters in method
+ 
+### Classes
+- Defining a Class
+- Constructor
+- Accessing methods levels
+- Accessing instance variables
+ 
+### Module
+- Mixin
+- Module as Namespace
+- Modules and Class Composition

arrays.md

@@ -14,37 +14,40 @@ array_3 << 3 # Insert 3 to array_3
 => [1, 2, 3]
 ```
 
-## Index
+## Indexing
+- Array indexing start at 0 for first element, the second gets 1, and so on.
+- An index of -1 indicates the last element of the array, -2 is the next to last element in the array, and so on.
 
 ```ruby
 Array: [5, 2, 4, 7, 9]
         |  |  |  |  |
 Index:  0  1  2  3  4
 ```
-That mean: The first element gets the index 0. The second gets 1, and so on.
 
 ```ruby
 array = [5, 2, 4, 7, 9]
-array[0] # => 5 
-array[1] # => 2 
-array[4] # => 9
+array[0]  # => 5 
+array[1]  # => 2 
+array[4]  # => 9
+array[-1] # => 9
 ```
 
-## Common methods
+## Accessing elements
+
 - Get first element in array
 ```ruby
 array = [5, 2, 4, 7, 9]
-array[0]    # => 5
-array.first # => 5
-
+array[0]     # => 5
+array.first  # => 5
 ```
 
 - Get last element in array
 ```ruby
 array = [5, 2, 4, 7, 9]
-array.last # => 9
-array[4]   # => 9
-array[-1]  # => 9
+array.last  # => 9
+array[4]    # => 9
+array[-1]   # => 9
+
 ```
 
 - Get second of last element in array
@@ -53,10 +56,109 @@ array = [5, 2, 4, 7, 9]
 array[-2]  # => 7
 ```
 
-- Check a particular value in array
+- Get first n elements in array
+```ruby
+array = [5, 2, 4, 7, 9]
+array.first(3)  # => [5, 2, 4]
+```
+
+- Get last n elements in array
 ```ruby
 array = [5, 2, 4, 7, 9]
+array.last(2)  # => [7, 9]
+```
+
+## Iteration
+### each
+
+You can iterate elements in array:
+```ruby
+[3, 4, 5].each{ |i| puts "element: #{i}" }
+# Output:
+element: 3
+element: 4
+element: 5
+ => [3, 4, 5]
+```
+
+You can iterate over nested arrays:
+```ruby
+[[1, 2], [3, 4], [7, 8]].each do |a, b| 
+  puts "a: #{a}, b: #{b}" 
+end
+# Output:
+a: 1, b: 2
+a: 3, b: 4
+a: 7, b: 8
+ => [[1, 2], [3, 4], [7, 8]]
+```
+
+### each_with_index
+You can iterate elements with index in array:
+
+```ruby
+[3, 4, 5].each_with_index do |element, index|
+  puts "Index #{index}: element is #{element}"
+end
+# Output
+Index 0: element is 3
+Index 1: element is 4
+Index 2: element is 5
+```
+
+## Filtering with *select*, *reject*
 
+- *select*: will returen elements match to the condition
+```ruby
+array = [5, 2, 4, 7, 9]
+array.select{|item| item > 5} # => [7, 9]
+```
+
+- *reject*: will returen elements do not match to the condition
+```ruby
+array = [5, 2, 4, 7, 9]
+array.reject{|item| item > 5} # => [5, 2, 4]
+```
+
+## map: 
+Create new array by invoke a block on each element of array.
+
+```ruby
+array = [1, 2, 3]
+array.map{|item| item * 2}  # => [2, 4, 6]
+array.map{|item| item.to_s} # => ["1", "2", "3"]
+array.map(&:to_s)           # => ["1", "2", "3"]
+```
+
+## Common methods
+
+- Count numbers of elements of array with #count, #length or #size
+
+```ruby
+array = [1, 2, 4, 7, 9]
+array.count    # => 5
+array.length   # => 5
+array.size     # => 5
+```
+
+- Remove all nil elements in array with #compact and #compact!
+
+```ruby
+array = [5, nil, 4, 7, 9, nil]
+# It return new copy array with nil removed
+# Without effecting the origin array
+array.compact    #=> [5, 4, 7, 9]
+array            #=> [5, nil, 4, 7, 9, nil]
+
+# It effect to origin array
+array.compact!   #=> [5, 4, 7, 9]
+array            #=> [5, 4, 7, 9]
+```
+
+- Check a particular value in array with #include?
+
+```ruby
+array = [5, 2, 4, 7, 9]
 array.include?(4)
 => true
 

comments.md

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+# Comments
+
+## What is a comment?
+- Are line of annotations within Ruby code that are ignored at runtime.
+- We use comment to make source code easier to understand.
+
+## Single line comments
+A single line comment start with # character
+
+```ruby
+# This is a single line comment
+puts 'Welcome to comment section'
+```
+
+When executed, output of above program will *Welcome to comment section*
+
+## Multiline comments
+Multiline comments using by =begin and =end syntax
+
+```ruby
+=begin 
+This is a multiline comment
+Write your comment here
+=end
+puts 'Welcome to comment section'
+```
+