PERL/C2/while-do-while-loops/English-timed

Visual Cue	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 Linux12.04 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 is equal 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 close double quote 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 increments 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, 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 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