Ruby/C2/Variables-in-Ruby/English - Revision history

Nancyvarkey at 14:03, 18 August 2013

2013-08-18T14:03:46Z

Sneha at 06:35, 16 April 2013

2013-04-16T06:35:04Z

Afrin: Created page with ''''Title of script''': Variables in Ruby '''Author: Afrin pinjari''' '''Keywords: to_s, to_i, video tutorial, local variable, global variable''' {| style="border-spacing:0;…'

2013-01-08T12:28:19Z

Created page with ''''Title of script''': Variables in Ruby '''Author: Afrin pinjari''' '''Keywords: to_s, to_i, video tutorial, local variable, global variable''' {| style="border-spacing:0;…'

New page

'''Title of script''': Variables in Ruby

'''Author: Afrin pinjari'''

'''Keywords: to_s, to_i, video tutorial, local variable, global variable'''

{| style="border-spacing:0;"
! <center>Visual Clue</center>
! <center>Narration</center>

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 1
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| <center>Welcome to the Spoken Tutorial on </center>

<center>Variables in '''Ruby'''</center>

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 2

Learning Objectives
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| In this tutorial we will learn

* What is a variable?
* Dynamic typing in '''Ruby'''
* Declaring a variable
* Converting variable types
* What is variable's scope?
* Types of variables

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 3

System Requirements
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Here we are using

* '''Ubuntu''' Linux version 12.04
* '''Ruby''' 1.9.3

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 4

Pre-requisites
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| To follow this tutorial you must have knowledge of using''' Terminal''' in '''Linux.'''

You must also be familiar with '''irb'''

If not, for relevant tutorials, please visit our website

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 5

Variables
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Now I will explain what a variable is.

* Variable is used to store a value.
* Variable is a reference that can be assigned.
* Please note that '''Ruby '''variables are''' case sensitive.'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 6

Variables

| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| * Variable names should be '''meaningful'''.
* Variable name may only contain lowercase letters, numbers and underscores.
* Ex : first_name

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 7

Dynamic Typing
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Now''' '''let us see what is dynamic typing

* '''Ruby''' is a dynamic typed language.
* It means that you '''don't''' need to declare '''datatype''' while creating a variable.

* '''Ruby interpreter '''determines the data type at the time of assignment.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"|
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Now let us see how to declare a variable in '''Ruby.'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Press '''Ctrl+Alt+t'''

Switch to the terminal
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Open the terminal by pressing '''Ctrl,Alt''' and''' T '''keys simultaneously.

A terminal window appears on your screen.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Type

'''irb'''<nowiki><<Press </nowiki>'''Enter'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Type''' '''

'''irb'''

Press '''Enter '''to launch '''Interactive Ruby'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Type

'''var1=10 '''<nowiki><<press </nowiki>'''Enter'''

| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Now type

'''var1''' equal to '''10 '''

Press '''Enter'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''var1'''

Highlight '''10'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Here we have declared a variable '''var1''' and assigned a value '''10 '''to it'''.'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"|
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Let's check whether the datatype allotted by the interpreter is

'''integer '''or not''' . '''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Type

'''var1.kind_of?Integer '''<nowiki><< press </nowiki>'''Enter'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| So, type

'''var1 '''dot '''kind''' underscore '''of '''question mark '''Integer'''

and press '''Enter'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''true'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| We will get the output as '''true.'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"|
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| In''' Ruby''' you can dynamically change the variable type.

To do so, just assign a new value to it.

Let's do this by assigning a '''string''' value to variable '''var1.'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Type

'''var1=”hello”'''<nowiki><< press </nowiki>'''Enter'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Type

'''var1''' equal to within double quote '''hello'''

press Enter

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Type

'''<nowiki>var1.class<< </nowiki>'''press '''Enter'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Let's verify the variable type assigned

Type

'''var1''' dot '''class '''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight''' .class'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Class method tells us what class of variable it is

Press''' Enter'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''string'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| We get the output as '''string'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"|
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| '''Ruby '''has automatically changed the variable type from '''integer''' to '''string'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 7

Converting variable types

Highlight '''to_s'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| We will now learn how to convert a variable value to different type

Lets switch back to slides

'''Ruby''' variable classes have methods to convert their value to a different type

* '''to_i '''method is used to convert a variable to '''integer'''
* '''to_f '''method is used to convert a variable to '''floating point value'''
* '''to_s''' method is used to convert a variable to''' string'''<br/>

The '''to _''' '''s()''' method takes number base as an argument.

The conversion depends on this number base.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| '''Press Ctrl+L'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Now let us try out these methods.

Go to the''' terminal'''

Lets clear the terminal first

Press Ctrl,l to clear the '''irb '''console

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Type

'''<nowiki>y=20<<</nowiki>'''press''' '''Enter
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Type

'''y '''equal to '''20'''

Press''' '''Enter

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''y''' and '''20'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Here we have declared a variable''' y''' and assigned a value '''20''' to it.

We will now convert '''y''' to a floating point value using '''to '''underscore''' f''' method

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Type

'''<nowiki>y.to_f<< </nowiki>'''press''' Enter'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Type

'''y '''dot '''to '''underscore '''f'''

Press '''Enter'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight''' 20.0'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| We will get the value as float'''.'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Type

'''<nowiki>y.to_s<<</nowiki>''' press''' Enter'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Now Type

'''y '''dot '''to '''underscore '''s.'''

Press '''Enter'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''“20”'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| We will get output '''20 '''within double quotes

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"|
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| To convert variable '''y''' in binary form give number base as '''2''' in '''to_s''' method

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Press '''Up Arrow'''

| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Press up arrow key to get the previous command

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Type

y.to_s'''<nowiki>(2)<<</nowiki>'''press''' Enter'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Now type

opening bracket 2 closing bracket

press '''Enter'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''10100'''
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| We will get the output''' 10100 '''in binary form

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"|
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Similarly you can convert variable '''y''' to '''octal''' or '''hexadecimal''' form

By changing the number base to 8 or 16.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"|
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Let us switch back to our slide

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 8

Variable Scope
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| We will now learn what is '''variable scope'''.

'''Scope''' defines where in a program a variable is accessible.

'''Ruby''' has four types of variable scope:

* '''Local'''
* '''Global'''
* '''Instance '''
* '''Class '''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 9

Naming Convention
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Each variable type is declared by using a special character

At the beginning of the variable name

Name Beginning With Variable Scope

'''$ '''A '''global''' variable

'''<nowiki>[a-z] or _ </nowiki>'''A '''local''' variable

'''@ '''An '''instance''' variable

'''@@ '''A '''class''' variable

'''<nowiki>[A-Z]</nowiki>''' A '''constant'''

'''$ '''represents '''global''' variable

Lower case letters with underscore represents a '''local''' variable

'''@''' represents an '''instance''' variable

Two''' @@''' represents a '''class''' variable

Upper case letters represents a '''constant'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"|
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| We will learn in detail about this in another tutorial.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"|
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| <nowiki><<Pause>></nowiki>

This brings us to the end of this Spoken Tutorial.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 11

Summary
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| In this tutorial we have learnt

* To declare a variable <br/> eg var1=10
* Changing variable type using to_f, to_s methods
* Different Variable '''scope'''

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 13

Assignment
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| As an assignment

Declare a variable and convert it to '''octal''' and '''hexadecimal''' form

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 14

About the Spoken Tutorial Project
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Watch the video available at the following link.

It summarises the Spoken Tutorial project.

If you do not have good bandwidth, you can download and watch it.

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 15
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| The Spoken Tutorial Project Team :

Conducts workshops using spoken tutorials

Gives certificates to those who pass an online test

For more details, please write to

contact at spoken hyphen tutorial dot org

|-
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Slide 16

Acknowledgement
| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Spoken Tutorial Project is a part of the Talk to a Teacher project.

It is supported by the National Mission on Education through ICT, MHRD, Government of India.

More information on this Mission is available at:

spoken hyphen tutorial dot org slash NMEICT hyphen Intro.

This is Afrin Pinjari from IIT Bombay, signing off.

Thank you for watching.

|}

@@ Line 197: / Line 197: @@
 |-
 | style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight''' .class'''
-| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Class method tells us what class of variable it is
+| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Class method tells us what class of variable it is and
-Press''' Enter'''
+ Now Press''' Enter'''
 |-
@@ Line 249: / Line 249: @@
 '''<nowiki>y=20<<</nowiki>'''press''' '''Enter
-| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Type
+| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Now Type
 '''y '''equal to '''20'''
-Press''' '''Enter
+ and Press''' '''Enter
 |-
 | style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''y''' and '''20'''
-| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Here we have declared a variable''' y''' and assigned a value '''20''' to it.
+| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Here we have declared a variable called''' y''' and assigned a value '''20''' to it.
 We will now convert '''y''' to a floating point value using '''to '''underscore''' f''' method
@@ Line 267: / Line 267: @@
 | style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Type
-'''y '''dot '''to '''underscore '''f'''
+'''y '''dot '''to '''underscore '''f''' and
 Press '''Enter'''
@@ Line 281: / Line 281: @@
 | style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Now Type
-'''y '''dot '''to '''underscore '''s.'''
+'''y '''dot '''to '''underscore '''s.'''and
 Press '''Enter'''
@@ Line 306: / Line 306: @@
 | style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| Now type
-opening bracket 2 closing bracket
+opening bracket 2 closing bracket and
 press '''Enter'''
@@ Line 312: / Line 312: @@
 |-
 | style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:none;padding:0.097cm;"| Highlight '''10100'''
-| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| We will get the output''' 10100 '''in binary form
+| style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| We will get the output''' 10100 '''in the  binary form
 |-
@@ Line 368: / Line 368: @@
 '''$ '''represents '''global''' variable
-Lower case letters with underscore represents a '''local''' variable
+Lower case letters and underscore represents a '''local''' variable
 '''@''' represents an '''instance''' variable
@@ Line 387: / Line 387: @@
 | style="border-top:none;border-bottom:1pt solid #000000;border-left:1pt solid #000000;border-right:1pt solid #000000;padding:0.097cm;"| <nowiki><<Pause>></nowiki>
-This brings us to the end of this Spoken Tutorial.
+This brings us to the end of this Spoken Tutorial.let us summarise
 |-