PERL/C3/Referencing-and-Dereferencing/English-timed - Revision history

PoojaMoolya at 12:43, 20 February 2017

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Sandhya.np14 at 10:58, 5 February 2016

2016-02-05T10:58:06Z

Sandhya.np14 at 07:35, 5 February 2016

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Sandhya.np14 at 12:40, 4 February 2016

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Sandhya.np14 at 07:38, 4 February 2016

2016-02-04T07:38:21Z

Sandhya.np14 at 12:57, 28 December 2015

2015-12-28T12:57:15Z

Sandhya.np14 at 05:44, 28 December 2015

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PoojaMoolya at 05:36, 26 November 2015

2015-11-26T05:36:41Z

PoojaMoolya at 09:46, 23 November 2015

2015-11-23T09:46:42Z

PoojaMoolya: Created page with " {| Border = 1 | ''' Time ''' | '''Narration''' |- | 00:01 | Welcome to the''' Spoken Tutorial''' on''' Referencing and Dereferencing in..."

2015-11-23T09:45:17Z

Created page with " {| Border = 1 | <center>''' Time '''</center> | <center>'''Narration'''</center> |- | 00:01 | Welcome to the''' Spoken Tutorial''' on''' Referencing and Dereferencing in..."

New page

{| Border = 1
| <center>''' Time '''</center>
| <center>'''Narration'''</center>

|-
| 00:01
| Welcome to the''' Spoken Tutorial''' on''' Referencing and Dereferencing in Perl.'''

|-
| 00:07
| In this tutorial we will learn about
* '''Scalar References'''
* '''Array References'''
* '''Hash References'''
* '''Dereferences''' and
* How to add, remove, access '''elements''' of '''array/hash references'''

|-
| 00:22
| For this tutorial, I am using
* '''Ubuntu Linux 12.04''' operating system
* '''Perl 5.14.2'''
* '''gedit Text Editor'''

|-
| 00:33
|You can use any text editor of your choice.

|-
| 00:37
| You should have working knowledge of
* '''Perl''' programming
* '''Array functions''' and
* '''Hash functions'''.

|-
| 00:43
|If not, then go through the relevant''' Perl''' tutorials on this website.

|-
| 00:49
| What is''' References'''?

|-
| 00:51
|A''' reference''' is a '''pointer''' or an '''address''' to '''a variable, array, hash''' or a '''subroutine'''.

|-
| 00:58
|It does not contain data directly.

|-
| 01:01
|'''Reference''' is an easy, compact '''scalar''' value.

|-
| 01:05
| '''Reference''' will improve the performance of '''Perl''' code when you pass or return large data structures.

|-
| 01:12
|It saves memory as it passes a''' reference''' to a '''subroutine''' rather than passing a value.

|-
| 01:18
|Easy to manage complicated '''Perl''' data structures.

|-
| 01:22
| Let us learn how to create a '''reference'''.

|-
| 01:25
| We can create a''' reference''' for any '''variable, subroutine''' or value, by putting a '''backslash (\)''' in front of it.

|-
| 01:33
|A''' scalar variable''' is''' referenced''' by '''backslash''' and '''dollar sign''' ($) as shown here.

|-
| 01:39
|An''' array variable''' is''' referenced''' by '''backslash''' and '''at the rate(@)''' symbol.

|-
| 01:45
|A''' hash variable''' is''' referenced''' by '''backslash''' and '''percentage(%)''' symbol as shown in the example here.

|-
| 01:53
| what is '''dereference'''?

|-
| 01:55
|When a '''reference''' is''' dereferenced''', the actual value is returned.

|-
| 02:00
|'''Dereference''' is done by enclosing the''' reference''' variable within curly brackets.

|-
| 02:06
|And preceding the left curly bracket with a character denoting the type of''' reference''' it is.

|-
| 02:12
| Let us see how to''' dereference''' variables.

|-
| 02:16
| A''' scalar variable''' is dereferenced by '''dollar sign ($)''' and curly brackets.

|-
| 02:21
|An''' array variable''' is dereferenced by '''at the rate (@)''' symbol and curly brackets.

|-
| 02:27
|A''' hash variable''' is dereferenced by '''percentage(%)''' symbol and curly brackets.

|-
| 02:33
| Let us see a simple program for''' Scalar reference''' and''' dereference.'''

|-
| 02:38
| Let me open a sample program in''' gedit Text editor.'''

|-
| 02:43
| Open the '''terminal''' and type''' gedit scalarRef dot pl ampersand''' and press '''Enter'''.

|-
| 02:50
| Type the following code as displayed on the screen

|-
| 02:55
| Let me explain the code.

|-
| 02:57
|First line declares a '''scalar variable '$a'''' and initialized to 10.

|-
| 03:03
|As mentioned earlier, a '''scalar variable''' is''' referenced''' by '''backslash''' and '''dollar sign ($)'''

|-
| 03:10
|This line will print '''memory address''' of the '''variable''' that is created as''' reference'''.

|-
| 03:16
|To print the actual value, the '''variable''' is''' dereferenced''' by curly brackets preceded by '''$'''.

|-
| 03:23
|Here'''ref()''' function will return the''' reference''' type such as '''scalar''' or '''array''' or '''hash'''.

|-
| 03:30
| Now, press''' Ctrl+S''' to save the file.

|-
| 03:34
| Let us execute the program.

|-
| 03:36
| Switch to the '''terminal''' and type '''perl scalarRef dot pl''' and press''' Enter'''.

|-
| 03:43
| The output is displayed as shown.

|-
| 03:46
|First line shows the memory address where the value 10 is stored.

|-
| 03:51
|The second line returns the actual value 10.

|-
| 03:55
|'''Ref() function '''returns ''''Scalar'''' as output.

|-
| 03:59
| Next, let us understand how to create a''' reference''' and''' dereference''' array by using a sample program.

|-
| 04:07
| I already have a sample program. Let me open it in''' gedit Text editor.'''

|-
| 04:13
| In the '''terminal''', type''' gedit arrayRef dot pl ampersand''' and press '''Enter'''.

|-
| 04:20
| Type the following code as displayed on the screen in the '''arrayRef dot pl''' file.

|-
| 04:26
| Let me explain the code now.

|-
| 04:28
|Here, in the first line, I have declared an '''array @color''' and initialised it with three values.

|-
| 04:35
|It is''' referenced''' with '''backslash @color''' which is the '''array name''' and assigned to''' $colorRef.'''

|-
| 04:42
|The '''print''' statement will print the''' reference''' value and the''' dereferenced''' value.

|-
| 04:47
| Now, press''' Ctrl+S''' to save the file.

|-
| 04:51
| Let us execute the program.

|-
| 04:53
| Switch back to the '''terminal''' and type '''perl arrayRef dot pl''' and press''' Enter'''.

|-
| 05:00
| The output is displayed as shown here

|-
| 05:04
| The first line shows the output of the '''memory address''' of the variable that is created as''' reference'''.

|-
| 05:10
|The second line shows the actual value that is''' dereferenced'''.

|-
| 05:16
| Next, we will see how to declare '''direct reference''' for an '''array'''.

|-
| 05:21
|Let’s come back to our program.

|-
| 05:24
|I have changed the existing program to show the '''direct reference''' for an '''array'''.

|-
| 05:29
| You can create a '''direct reference''' for an''' array''' by using square brackets<nowiki> [] </nowiki>as shown.

|-
| 05:35
|Use '''arrow operator (->)''' to '''dereference'''.

|-
| 05:39
|'''print''' statement will print ''''Green'''' as output.

|-
| 05:43
|Here the '''print''' statement takes the value of index<nowiki>[1]. </nowiki>i.e '''Green''' in our program.

|-
| 05:50
| Press''' Ctrl+S''' to save the file.

|-
| 05:54
| Switch back to the '''terminal''' and type '''perl arrayRef dot pl''' and press''' Enter''' to execute.

|-
| 06:03
| I’ll show an example on how to use the direct hash reference in the same code file.
So, let’s switch to '''gedit'''.

|-
| 06:11
| You can create a '''direct reference''' to hash by using curly brackets {} as shown here.

|-
| 06:18
| Use '''arrow operator (->)''' to dereference it. '''“Name”''' is the '''hash key'''.

|-
| 06:24
| On executing this block of code, both the '''print''' statements will print ''''Sunil'''' as output.

|-
| 06:31
| Next we will see how to add, remove, access '''elements''' to '''array reference''' with a sample program.

|-
| 06:39
| I already have a sample program. Let me open it in''' gedit Text editor'''

|-
| 06:45
| Open the''' terminal''' and type''' gedit arrayRefadd dot pl ampersand '''and press''' Enter'''

|-
| 06:54
| '''arrayRefadd.pl''' file is now open in''' gedit.''' Type the code as shown here in your file.

|-
| 07:02
| The first line initializes an array.

|-
| 07:06
| We have '''referenced''' an '''array''' with '''backslash @numarray''' and assigned to''' $ref.'''

|-
| 07:13
| Now, we will see how to access a particular '''element''' from the''' array reference.'''

|-
| 07:19
| We need to use the '''array index''' in square brackets<nowiki> “[ ]” </nowiki>to access the particular value. And an '''arrow operator (“->”)''' to''' dereference''' it.

|-
| 07:28
| The '''print''' statement will print the value of index<nowiki>[0]</nowiki>

|-
| 07:32
| '''Push function '''adds '''elements''' at the last position of an''' array reference.'''
In our case 5,6,7 is added to at the end of the existing array 1,2,3,4.

|-
| 07:47
| This '''print''' statement shows the output after adding to the''' array reference.'''

|-
| 07:53
| '''Pop function '''removes an element from the last position of an''' array reference'''

|-
| 07:58
| In our example, 7 will be removed from the existing''' array reference.'''

|-
| 08:03
| '''print '''statement shows the output after deleting from the''' array reference.'''

|-
| 08:08
| Now, press''' Ctrl+S''' to save the file.

|-
| 08:11
| Let us execute the program.

|-
| 08:14
| Switch back to the '''terminal''' and type '''perl arrayRefadd dot pl''' and press''' Enter'''.

|-
| 08:22
| The output is displayed as shown here

|-
| 08:26
| Now let us see another sample program to add, remove, and access '''elements''' of''' hash reference.'''

|-
| 08:34
| In the '''terminal''' type '''gedit hashRefadd dot pl ampersand''' and press '''Enter'''.

|-
| 08:42
| This will open the file''' hashRefadd.pl''' in''' gedit'''.

|-
| 08:47
| Let me explain the sample program.

|-
| 08:50
| I have declared a '''direct hash reference''' that can be stored in a '''scalar''' variable''' $weektemp.'''

|-
| 08:57
| I have used curly brackets to represent the''' hash reference''' and the '''arrow operator''' to''' dereference'''.

|-
| 09:04
| This code stores the temperature values from Monday to Friday.

|-
| 09:09
| I am using the '''“keys” built-in function''' to loop through the '''keys''' of the '''hash'''.

|-
| 09:15
| '''print''' statement will print each element of the '''hash'''.

|-
| 09:19
| We can access the particular value of an '''element''' as shown here.

|-
| 09:25
| '''print''' statement will print the temperature on Monday.

|-
| 09:29
| Now, save the file.

|-
| 09:32
| Switch to '''terminal''' and type '''perl hashRefadd dot pl''' and press''' Enter '''to see the output.

|-
| 09:41
| The '''hash keys '''and '''hash values''' are stored in a random order.

|-
| 09:46
| The displayed output is not related to the order in which they were added.

|-
| 09:52
| With this, we come to the end of this tutorial. Let us summarize.

|-
|09:57
| In this tutorial, we learnt about:

* '''Scalar References'''
* '''Array References'''
* '''Hash References'''
* '''Dereferences''' and
* How to add, remove, access '''elements''' of '''array/hash references''' with examples.

|-
| 10:14
| Here is an assignment for you.
Add new keys “'''Saturday'''” and “'''Sunday'''” in hash '''weektemp''' in our''' hashRefadd dot pl file.'''

|-
| 10:24
| Delete key “'''Saturday'''” at the end.

|-
| 10:27
| Print hash '''weektemp.'''

|-
| 10:30
| Save and execute the program. Now check the result.

|-
| 10:35
| The video at the following link summarises the Spoken Tutorial project.
Please download and watch it

|-
| 10:42
| We conduct workshops and give certificates for those who pass our online tests.
For more details, please write to us.

|-
| 10:51
| Spoken Tutorial project is funded by NMEICT, MHRD, Government of India.
More information on this mission is available at this link.

|-
| 11:02
| This is Nirmala Venkat from IIT Bombay, signing off. Thanks for watching.

|}

@@ Line 302: / Line 302: @@
 |-
 |  06:39
-|  I already have a sample program. Let me open it in''' gedit''' Text editor.
+|  I already have a sample program. Let me open it in''' gedit''' text-editor.
 |-
@@ Line 310: / Line 310: @@
 |-
 |  06:54
-|  'arrayRefadd.pl' file is now open in''' gedit.''' Type the code as shown here in your file.
+|  'arrayRefadd.pl' file is now open in''' gedit.''' Type the code as shown here, in your file.
 |-
@@ Line 334: / Line 334: @@
 |-
 |  07:32
-| '''Push()''' function adds '''elements''' at the last position of an''' array reference.'''
+| '''push()''' function adds '''elements''' at the last position of an''' array reference.'''
-In our case 5, 6, 7 are added to the end of the existing array 1, 2, 3, 4.
+In our case, 5, 6, 7 are added to the end of the existing array 1, 2, 3, 4.
 |-
@@ Line 343: / Line 343: @@
 |-
 |  07:53
-| '''Pop()''' function removes an '''element''' from the last position of an''' array reference'''.
+| '''pop()''' function removes an '''element''' from the last position of an''' array reference'''.
 |-

@@ Line 375: / Line 375: @@
 |-
 |  08:34
-|  In the '''terminal''', type: '''gedit hashRefadd dot pl ampersand'''  and press '''Enter'''.
+|  On the '''terminal''', type: '''gedit hashRefadd dot pl ampersand'''  and press '''Enter'''.
 |-

@@ Line 157: / Line 157: @@
 |-
 |  03:23
-|Here '''ref()''' function will return the''' reference''' type such as '''scalar''' or '''array''' or '''hash'''.
+|Here, '''ref()''' function will return the''' reference''' type such as '''scalar''' or '''array''' or '''hash'''.
 |-

@@ Line 11: / Line 11: @@
 | 00:07
 |  In this tutorial, we will learn about:
-* '''Scalar References'''
+'''Scalar References'''
-* '''Array References'''
+'''Array References'''
-* '''Hash References'''
+'''Hash References'''
-* '''Dereferences''' and
+'''Dereferences''' and
-* How to add, remove, access '''elements''' of '''array/hash references'''.
+How to add, remove, access '''elements''' of '''array/hash references'''.
 |-
 |  00:22
 |  For this tutorial, I am using:
-* '''Ubuntu Linux 12.04''' operating system
+'''Ubuntu Linux 12.04''' operating system
-* '''Perl 5.14.2'''
+'''Perl 5.14.2'''
-* '''gedit Text Editor'''
+'''gedit Text Editor'''
 |-
@@ Line 31: / Line 31: @@
 |  00:37
 |  You should have working knowledge of:
-* '''Perl''' programming
+'''Perl''' programming
-* '''Array functions''' and
+'''Array functions''' and
-* '''Hash functions'''.
+'''Hash functions'''.
 |-
@@ Line 436: / Line 436: @@
 |09:57
 | In this tutorial, we learnt about:
-* '''Scalar References'''
+'''Scalar References'''
-* '''Array References'''
+'''Array References'''
-* '''Hash References'''
+'''Hash References'''
-* '''Dereferences''' and
+'''Dereferences''' and
-* How to add, remove, access '''elements''' of '''array/hash references''' with examples.
+How to add, remove, access '''elements''' of '''array/hash references''' with examples.
 |-
@@ Line 460: / Line 460: @@
 |-
 |  10:35
-| The video at the following link summarizes the '''Spoken Tutorial''' project.
+| The video at the following link summarizes the '''Spoken Tutorial''' project.Please download and watch it.
 Please download and watch it.
 |-
 | 10:42
-| We conduct workshops and give certificates for those who pass our online tests.
+| We conduct workshops and give certificates for those who pass our online tests. For more details, please write to us.
 For more details, please write to us.
 |-

@@ Line 26: / Line 26: @@
 |-
 |  00:33
-|You can use any text editor of your choice.
+|You can use any text-editor of your choice.
 |-
@@ Line 41: / Line 41: @@
 |-
 |  00:49
-|  What is''' Reference'''?
+|  What is a''' Reference'''?
 |-

@@ Line 475: / Line 475: @@
 |-
 |  11:02
-|  This is Nirmala Venkat from IIT Bombay, signing off. Thanks for watching.
+|  This is Nirmala Venkat from '''IIT Bombay''', signing off. Thanks for watching.
 |}

@@ Line 404: / Line 404: @@
 |  09:15
 | '''print''' statement will print each element of the '''hash'''.
 |-
@@ Line 446: / Line 445: @@
 |-
 |  10:14
-| Here is an assignment for you.
+| Here is an assignment for you. Add new keys “'''Saturday'''” and “'''Sunday'''” in hash '''weektemp''' in our''' hashRefadd dot pl file.'''
- Add new keys “'''Saturday'''” and “'''Sunday'''” in hash '''weektemp''' in our''' hashRefadd dot pl file.'''
 |-