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

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 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 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