Difference between revisions of "PERL/C2/while-do-while-loops/English-timed"

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|Welcome to the spoken tutorial on '''while and do-while''' loops in '''Perl'''.
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|Welcome to the '''spoken tutorial''' on '''while and do-while loops''' in '''Perl'''.
 
   
 
   
 
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|* '''while''' loop in '''Perl'''  
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| '''while''' loop in '''Perl'''  
  
 
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|* '''do-while''' loop in '''Perl '''.
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| '''do-while''' loop in '''Perl '''.  I am using '''Ubuntu Linux 12.04''' operating system and '''Perl 5.14.2'''.
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| I am using '''Ubuntu Linux 12.04''' operating system and '''Perl 5.14.2'''.
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| You should have basic knowledge of "variables" and "comments" in ''' Perl.'''
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| You should have basic knowledge of '''variables''' and '''comments''' in ''' Perl.'''
 
   
 
   
 
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| Now Type the following code:  
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| Now type the following code:  
 
   
 
   
 
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|'''print''' space double quote '''Value of i''' colon ''' dollar i slash n'''  double quote complete semicolon
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|'''print''' space double quote '''Value of i''' colon ''' dollar i backslash n'''  double quote complete semicolon
 
   
 
   
 
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|press '''Enter '''.
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|press '''Enter'''.
 
   
 
   
 
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| Now again, the loop condition ''' $i<=4''' will be evaluated.  
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|Now again, the loop condition ''' $i<=4''' will be evaluated.  
 
   
 
   
 
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|''' perl whileLoop dot pl'''
 
|''' perl whileLoop dot pl'''
 
   
 
   
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|piece of code to be executed while the condition is true  
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|'''print''' space double quote '''Value of i colon <space> dollar i slash n'''  double quote complete semicolon  
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|'''print''' space double quote '''Value of i colon <space> dollar i backslash n'''  double quote complete semicolon  
 
   
 
   
 
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| If the condition is true, the loop will be executed again.  
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| If the condition is '''True''', the loop will be executed again.  
  
 
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|  The loop will get executed till the condition becomes false that is when variable 'i' becomes 5.  
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|  The loop will get executed till the condition becomes '''False''' that is when variable 'i' becomes 5.  
 
   
 
   
 
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|The condition is not true. So the loop will exit.  
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|The condition is not '''True'''. So, the loop will exit.  
  
 
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|This message was what we printed inside the while loop.  
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|whereas '''while''' loop does not get executed even once when the condition specified is false.  
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|whereas '''while''' loop does not get executed even once when the condition specified is '''False'''.  
  
 
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|Here is assignment for you -  
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|Here is an assignment for you -  
  
 
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| The Spoken Tutorial Project Team:  
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|The Spoken Tutorial Project Team:  
  
 
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|Gives certificates to those who pass an online  test.
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Latest revision as of 15:12, 10 March 2017

Time Narration
00:01 Welcome to the spoken tutorial on while and do-while loops in Perl.
00:06 In this tutorial, we will learn about:
00:09 while loop in Perl
00:11 do-while loop in Perl . I am using Ubuntu Linux 12.04 operating system and Perl 5.14.2.
00:20 I will also be using the gedit Text Editor.
00:24 You can use any text editor of your choice.
00:28 You should have basic knowledge of variables and comments in Perl.
00:33 Knowledge of for and foreach loops in Perl will be an added advantage.
00:38 Please go through the relevant spoken tutorials on the "Spoken Tutorial" website.
00:43 while loop in Perl:
00:45 The while loop executes a block of code while a condition is true.
00:50 The syntax of while loop is as follows -
00:53 while space open bracket condition close bracket
00:58 open curly bracket
01:00 piece of code to be executed while the condition is true
01:04 close curly bracket.
01:07 So, what happens if the condition is not satisfied? Then the while loop will exit without executing the code within, even once.
01:16 Now let us look at an example of while loop.
01:19 Open the Terminal and type:
01:22 gedit whileLoop dot pl space ampersand
01:29 and press Enter.
01:31 This will open the whileLoop.pl file in gedit.
01:34 Now type the following code:
01:37 hash exclamation mark slash u s r slash bin slash perl
01:45 press Enter.
01:47 'dollar i' ($i) equals to zero semicolon
01:52 press Enter .
01:54 while open bracket dollar i less than or equal to four close bracket space
02:04 open curly bracket press Enter and type:
02:08 print space double quote Value of i colon dollar i backslash n double quote complete semicolon
02:20 press Enter.
02:22 dollar i plus plus semicolon
02:27 press Enter and close the curly bracket.
02:31 Let me explain the while loop in detail.
02:33 We have initialized the variable 'i' to 0.
02:38 Now, we have specified the condition for while loop as $i less than or equal to 4.
02:46 If the 'condition' is true, the code within the while loop will get executed.
02:52 This means, first time our while loop will print "Value of i: 0" on the terminal.
03:01 Then the $i++ will increment the value of variable 'i' by one.
03:08 Now again, the loop condition $i<=4 will be evaluated.
03:16 And the loop will exit once the value of 'i' becomes 5.
03:22 In this case, while loop will get executed for i equal to 0, 1, 2, 3 and 4.
03:32 Press Ctrl+s to save the file.
03:35 Now, switch to the terminal.
03:37 Type the following to check for any compilation or syntax error:
03:42 perl hyphen c whileLoop dot pl
03:47 and press Enter.
03:49 The following line will be displayed on the terminal.
03:52 whileLoop.pl syntax OK
03:56 As there is no compilation or syntax error, we will execute the Perl script by typing:
04:02 perl whileLoop dot pl
04:06 and press Enter.
04:09 The following output will be displayed on the terminal.
04:14 Now, let us look at do-while loop.
04:20 The do..while statement will always execute the piece of code at-least once.
04:25 It will then check the condition and repeat the loop while the condition is true.
04:30 The syntax for do-while loop is as follows:
04:34 do space
04:36 open curly bracket
04:38 piece of code to be executed while the condition is true
04:42 close curly bracket then space
04:45 while space within the brackets condition and then semicolon.
04:50 Open the Terminal and type:
04:54 gedit doWhileLoop dot pl space ampersand
05:03 and then press Enter.
05:05 This will open doWhileLoop.pl file in gedit.
05:09 Type the following piece of code:
05:11 hash exclamation mark slash u s r slash bin slash perl Press Enter.
05:21 dollar i equals to zero semicolon press Enter.
05:27 do space
05:29 open curly bracket Enter type:
05:33 print space double quote Value of i colon <space> dollar i backslash n double quote complete semicolon
05:46 press Enter .
05:48 dollar i plus plus semicolon
05:52 press Enter .
05:54 close curly bracket.
05:56 space while space open bracket dollar i less than or equal to four
06:06 close bracket semicolon.
06:10 Here is the detail explanation of a do-while loop.
06:13 We have initialized the variable i to 0.
06:18 First time, the do-while loop will print the output as 'Value of i colon 0' on the terminal without checking for condition.
06:28 $i++ will increment the value of variable 'i' by one, each time loop gets executed.
06:36 Second time, the condition '$i' less than or equal to 4 will be checked.
06:43 If the condition is True, the loop will be executed again.
06:48 In our case, second time the output displayed on terminal will be 'Value of i colon 1'.
06:57 The loop will get executed till the condition becomes False that is when variable 'i' becomes 5.
07:05 Press Ctrl+s to save the file.
07:09 Now, switch to terminal and type the following to check for any compilation or syntax error.
07:16 perl hyphen c doWhileLoop dot pl
07:21 and press Enter.
07:23 The following line will be displayed on the terminal:
07:26 doWhileLoop.pl syntax OK
07:30 As there is no compilation or syntax error, we will now execute the Perl script.
07:36 Type: perl doWhileLoop dot pl
07:41 and press Enter.
07:43 The following output will be displayed on the terminal.
07:48 Now, let us see the actual difference between while and do-while loops.
07:53 On the Terminal, type:
07:55 gedit loop dot pl space ampersand
08:01 and press Enter.
08:03 This will open loop dot pl file in gedit.
08:07 Now type the piece of code shown.
08:12 We have declared a variable count and initialized it to zero.
08:19 In the while loop condition, we are checking if the variable count is greater than zero.
08:29 The condition is not true. So, the while loop code will not be executed even once.
08:36 In the do...while loop, we are first executing the code and then checking the condition.
08:44 So, the code will be executed at least once.
08:49 Then the condition whether the variable count is greater than zero, is checked.
08:57 The condition is not True. So, the loop will exit.
09:02 Now, press Ctrl+s to save the file.
09:05 Now, switch to terminal and type the following to check for any compilation or syntax errors.
09:12 perl hyphen c loop dot pl
09:16 and press Enter.
09:19 The following line will be displayed on the terminal.
09:22 loop dot pl syntax OK
09:26 As there is no compilation or syntax error, let us execute the Perl script
09:31 by typing perl loop dot pl
09:36 and press Enter.
09:38 The following output will be displayed on the terminal.
09:43 I am in do-while loop
09:46 Here we can see, there is no output message displaying 'I am in while loop' .
09:52 This message was what we printed inside the 'while' loop.
09:59 This implies that
10:01 do-while loop executes at-least once before evaluating the condition
10:07 whereas while loop does not get executed even once when the condition specified is False.
10:15 I hope the difference is clear to you now.
10:18 That's all there is to while and do-while loops.
10:22 Let us summarize.
10:24 In this tutorial, we have learnt:
10:26 while loop and do-while loop in Perl
10:29 using sample programs.
10:31 Here is an assignment for you -
10:33 Print 'Hello Perl'
10:35 till the count of variable reaches 10
10:38 by using while loop and do-while loops.
10:41 Watch the video available at the following link.
10:45 It summarizes the Spoken Tutorial project.
10:49 If you do not have good bandwidth, you can download and watch it.
10:53 The Spoken Tutorial Project Team:
10:56 Conducts workshops using spoken tutorials.
11:00 Gives certificates to those who pass an online test.
11:04 For more details, please write to contact at spoken hyphen tutorial dot org.
11:12 "Spoken Tutorial" project is a part of the "Talk to a Teacher" project.
11:17 It is supported by the National Mission on Education through ICT, MHRD, Government of India.
11:24 More information on this mission is available at spoken hyphen tutorial dot org slash NMEICT hyphen Intro.
11:36 Hope you enjoyed this Perl tutorial.
11:38 This is Amol Brahmankar, signing off.
11:40 Thanks for joining.

Contributors and Content Editors

Gaurav, PoojaMoolya, Sandhya.np14, Sneha

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