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

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| '''dollar i''' is equal to zero semicolon
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| 'dollar i' ($i) equals to zero semicolon
 
   
 
   
 
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| Press '''Enter '''
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| press '''Enter '''.
 
   
 
   
 
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|Open curly bracket press '''Enter''' and type  
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|open curly bracket press '''Enter''' and type:
 
   
 
   
 
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|02:08
 
|02:08
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|'''print''' space double quote '''Value of i''' colon,  ''' dollar i slash n''' close double quote semicolon
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|'''print''' space double quote '''Value of i''' colon ''' dollar i slash n''' double quote complete semicolon
 
   
 
   
 
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|Press '''Enter '''
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|press '''Enter '''.
 
   
 
   
 
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|Close the curly bracket  
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|close the curly bracket.
 
   
 
   
 
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| We have initialized the variable '''i''' to 0.  
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| We have initialized the variable 'i' to 0.  
  
 
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|02:38
 
|02:38
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|Now we have specified the condition for '''while''' loop as '''$i'''  less than or equal to 4.  
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|Now, we have specified the condition for '''while''' loop as '''$i'''  less than or equal to 4.  
 
   
 
   
 
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| If the '''condition''' is true, the code within the '''while''' loop will get executed.  
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| If the 'condition' is true, the code within the '''while''' loop will get executed.  
  
 
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|This means, first time our '''while''' loop will ''' print 'Value of i: 0' ''' on the terminal.  
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|This means, first time our '''while''' loop will print "Value of i: 0" on the terminal.  
 
   
 
   
 
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|Then the ''' $i++ ''' will increments the value of variable i by one.  
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|Then the '''$i++''' will increment the value of variable 'i' by one.  
  
 
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|And the loop will exit once the value of i becomes 5.  
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|And the loop will exit once the value of 'i' becomes 5.  
 
   
 
   
 
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| In this case, '''while''' loop will get executed for '''i''' equal to 0, 1, 2, 3, 4.   
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| In this case, '''while''' loop will get executed for '''i''' equal to 0, 1, 2, 3 and 4.   
 
   
 
   
 
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|  03:32
 
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| Press ctrl+s to save the file.  
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| Press '''Ctrl+s''' to '''save''' the file.  
 
   
 
   
 
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| Type the following to check for any compilation or syntax error -
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| Type the following to check for any compilation or syntax error: 
 
   
 
   
 
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|The following line will be displayed on the terminal  
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|The following line will be displayed on the terminal.
 
   
 
   
 
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|As there is no compilation or syntax error, we will execute the '''Perl''' script by typing -
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|As there is no compilation or syntax error, we will execute the '''Perl''' script by typing: 
 
   
 
   
 
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|and press '''Enter'''
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|and press '''Enter'''.
 
   
 
   
 
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| Now, let us look at '''do-while loop'''
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| Now, let us look at '''do-while loop'''.
  
 
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| The '''do...while''' statement will always execute the piece of code at-least once.  
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| The '''do..while''' statement will always execute the piece of code at-least once.  
 
   
 
   
 
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|The syntax for '''do-while ''' loop is as follows -
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|The syntax for '''do-while''' loop is as follows:
  
 
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|Piece of code to be executed while the condition is true  
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|piece of code to be executed while the condition is true  
 
   
 
   
 
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|'''while''' space within brackets '''condition''' and then semicolon  
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|'''while''' space within the brackets '''condition''' and then semicolon.
 
   
 
   
 
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|Open the Terminal and type;
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|Open the Terminal and type:
  
 
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|  and then press '''Enter'''
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|  and then press '''Enter'''.
  
 
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| Type the following piece of code -
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| Type the following piece of code: 
 
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|'''hash exclamation mark slash u s r slash bin slash perl'''  Press '''Enter'''
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|'''hash exclamation mark slash u s r slash bin slash perl'''  Press '''Enter'''.
 
   
 
   
 
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|'''dollar i equals to zero semicolon press enter'''
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|'''dollar i equals to zero''' semicolon press '''Enter'''.
  
 
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|open curly bracket enter type  
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|open curly bracket '''Enter''' type:
  
 
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Revision as of 21:31, 7 May 2015

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 .
00:12 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 slash n double quote complete semicolon
02:20 press Enter .
02:22 dollar i plus plus semicolon
02:27 press Enter and
02:28 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 slash n close double quote 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 get 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 are no compilation or syntax errors, 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 Open 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 are no compilation or syntax errors, 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 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 summaries 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 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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