Ruby Basic concepts...

   Ruby is a pure object oriented programming language. It was created in 1993 by Yukihiro Matsumoto of Japa
   Ruby is an open-source and is freely available on the Web, but it is subject to a license.
   Ruby is a general-purpose, interpreted programming language.
   Ruby is a true object-oriented programming language.
   Ruby is a server-side scripting language similar to Python and PERL.
   Ruby can be used to write Common Gateway Interface (CGI) scripts.
   Ruby can be embeded into Hypertext Markup Language (HTML).
   Ruby has a clean and easy syntax that allows a new developer to learn Ruby very quickly and easily.
   Ruby has similar syntax to that of many programming languages such as C++ and Perl.
   Ruby is very much scalable and big programs written in Ruby are easily maintainable.
   Ruby can be used for developing Internet and intranet applications.
   Ruby can be installed in Windows and POSIX environments.
   Ruby support many GUI tools such as Tcl/Tk, GTK, and OpenGL.
   Ruby can easily be connected to DB2, MySQL, Oracle, and Sybase.
   Ruby has a rich set of built-in functions which can be used directly into Ruby scripts.


##simple
def hello
out = "Hello World"
puts out
 end
hello
##o/p:Hello World
####The initialize method is a special type of method, which will be executed when the new method of the class is called with parameters####
class Customer
   @@no_of_customers=0
   def initialize(id, name, addr)
      @cust_id=id
      @cust_name=name
      @cust_addr=addr
   end
end
cust1=Customer.new("1", "John", "Wisdom Apartments, Ludhiya")
cust2=Customer.new("2", "Poul", "New Empire road, Khandala")
puts cust1.inspect
puts cust2.inspect
#o/p  <Customer:0x8a29ee8 @cust_id="1", @cust_name="John", @cust_addr="Wisdom Apartments, Ludhiya">
#<Customer:0x8a29e98 @cust_id="2", @cust_name="Poul", @cust_addr="New Empire road, Khandala">

#################33
class Sample
   def hello
      puts "Hello Ruby!"
   end
end

# Now using above class to create objects
object = Sample. new
object.hello

    Local Variables: Local variables are the variables that are defined in a method. Local variables are not available outside the method. You will see more detail about method in subsequent chapter. Local variables begin with a lowercase letter or _.
=====================================
    Instance Variables: Instance variables are available across methods for any particular instance or object. That means that instance variables change from object to object. Instance variables are preceded by the at sign (@) followed by the variable name.


class Customer
   def initialize(id, name, addr)
      @cust_id=id
      @cust_name=name
      @cust_addr=addr
   end
   def display_details()
      puts "Customer id #@cust_id"
      puts "Customer name #@cust_name"
      puts "Customer address #@cust_addr"
    end
end

# Create Objects
cust1=Customer.new("1", "John", "Wisdom Apartments, Ludhiya")
cust2=Customer.new("2", "Poul", "New Empire road, Khandala")

# Call Methods
cust1.display_details()
cust2.display_details()

o/p:Customer id 1
Customer name John
Customer address Wisdom Apartments, Ludhiya
Customer id 2
Customer name Poul
Customer address New Empire road, Khandala
=============================================================

    Class Variables: Class variables are available across different objects. A class variable belongs to the class and is a characteristic of a class. They are preceded by the sign @@ and are followed by the variable name.

class Customer
   @@no_of_customers=0
   def initialize(id, name, addr)
      @cust_id=id
      @cust_name=name
      @cust_addr=addr
   end
   def display_details()
      puts "Customer id #@cust_id"
      puts "Customer name #@cust_name"
      puts "Customer address #@cust_addr"
    end
    def total_no_of_customers()
       @@no_of_customers += 1
       puts "Total number of customers: #@@no_of_customers"
    end
end

# Create Objects
cust1=Customer.new("1", "John", "Wisdom Apartments, Ludhiya")
cust2=Customer.new("2", "Poul", "New Empire road, Khandala")

# Call Methods
cust1.total_no_of_customers()
cust2.total_no_of_customers()

o/p:
Total number of customers: 1
Total number of customers: 2


=====================================
    Global Variables: Class variables are not available across classes. If you want to have a single variable, which is available across classes, you need to define a global variable. The global variables are always preceded by the dollar sign ($).
ex:$global_variable = 10
class Class1
  def print_global
     puts "Global variable in Class1 is #$global_variable"
  end
end
class Class2
  def print_global
     puts "Global variable in Class2 is #$global_variable"
  end
end

class1obj = Class1.new
class1obj.print_global
class2obj = Class2.new
class2obj.print_global
o/p:Global variable in Class1 is 10
Global variable in Class2 is 10

=====================================
Ruby Constants:


class Example
   VAR1 = 100
   VAR2 = 200
   def show
       puts "Value of first Constant is #{VAR1}"
       puts "Value of second Constant is #{VAR2}"
   end
end

# Create Objects
object=Example.new()
object.show

Here VAR1 and VAR2 are constant. This will produce following result:

Value of first Constant is 100
Value of second Constant is 200


===========================
Ruby Pseudo-Variables:

They are special variables that have the appearance of local variables but behave like constants. You can not assign any value to these variables.

    self: The receiver object of the current method.

    true: Value representing true.

    false: Value representing false.

    nil: Value representing undefined.

    __FILE__: The name of the current source file.

    __LINE__: The current line number in the source file

=================================
Ruby Arrays:

Literals of Ruby Array are created by placing a comma-separated series of object references between square brackets. A trailing comma is ignored.

ary = [  "fred", 10, 3.14, "This is a string", "last element", ]
ary.each do |i|
   puts i
end
=======================
Ruby Hashes:

A literal Ruby Hash is created by placing a list of key/value pairs between braces, with either a comma or the sequence => between the key and the value. A trailing comma is ignored.
Example:

#!/usr/bin/ruby

hsh = colors = { "red" => 0xf00, "green" => 0x0f0, "blue" => 0x00f }
hsh.each do |key, value|
   print key, " is ", value, "\n"
end

This will produce following result:

green is 240
red is 3840
blue is 15
========================
Ruby Ranges:

A Range represents an interval.a set of values with a start and an end. Ranges may be constructed using the s..e and s...e literals, or with Range.new.

Ranges constructed using .. run from the start to the end inclusively. Those created using ... exclude the end value. When used as an iterator, ranges return each value in the sequence.

A range (1..5) means it includes 1, 2, 3, 4, 5 values and a range (1...5) means it includes 1, 2, 3, 4 values.
Example:

#!/usr/bin/ruby
(10..15).each do |n|
   print n, ' '
end
This will produce following result:
10 11 12 13 14 15
####ruby condtions
Ruby if...else, case, unless
#####ruby loops
while, for, until, break, redo and retry
for i in 0..5
   puts "Value of local variable is #{i}"end