Difference between revisions of "PERL/C2/while-do-while-loops/English-timed"
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Revision as of 18:04, 14 August 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 backslash 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. |
