Difference between revisions of "PERL/C2/while-do-while-loops/English-timed"
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Revision as of 15:40, 15 April 2013
| Visual Cue | Narration |
|---|---|
| 00.01 | Welcome to the spoken tutorial on while and do-while loops in Perl |
| 00.07 | In this tutorial, we will learn about;while loop in Perl |
| 00.11 | do-while loop in Perl |
| 00.13 | I am using Ubuntu Linux12.04 operating system and Perl 5.14.2
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| 00.21 | I will also be using the gedit Text Editor.
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| 00.25 | You can use any text editor of your choice. |
| 00.29 | You should have basic knowledge of Variables and Comments in Perl
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| 00.33 | Knowledge of for and foreach loops in Perl will be an added advantage.
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| 00.39 | Please go through the relevant spoken tutorials on the spoken tutorial website. |
| 00.44 | while loop in Perl
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| 00.46 | The while loop executes a block of code while a condition is true. |
| 00.50 | The syntax of while loop is as follows -
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| 00.53 | while space open bracket condition close bracket Open curly bracket
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| 01.00 | Piece of code to be executed while the condition is true. 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. |
| 01.17 | Now let us look at an example of while loop. |
| 01.20 | Open the Terminal' and type gedit whileLoop dot pl space ampersand and press Enter |
| 01.31 | This will open the whileLoop.pl file in gedit.
|
| 01.35 | Now Type the following code
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| 01.37 | hash exclamation mark slash u s r slash bin slash perl Press Enter.
|
| 01.47 | dollar i is equal to zero semicolon |
| 01.52 | Press Enter
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| 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
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| 02.08 | print space double quote Value of i colon dollar i slash n double quote complete semicolon |
| 02.21 | Press Enter
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| 02.23 | dollar i plus plus semicolon press enter and |
| 02.29 | Close the curly bracket |
| 02.31 | Let me explain the while loop in detail. |
| 02.34 | We have initialized the variable i to 0. |
| 02.39 | Now we have specified the condition for while loop as $i less than or equal to 4. |
| 02.47 | 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.
|
| 03.17 | 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. |
| 03.38 | Type the following to check for any compilation or syntax error -
|
| 03.43 | perl hyphen c whileLoop dot pl and press Enter. |
| 03.49 | The following line will be displayed on the terminal whileLoop.pl syntax OK |
| 03.56 | As there is no compilation or syntax error, we will execute the Perl script by typing -
|
| 04.03 | perl whileLoop dot pl and press Enter |
| 04.10 | The following output will be displayed on the terminal. |
| 04.15 | Now, let us look at do-while loop |
| 04.20 | The do...while statement will always execute the piece of code at-least once.
|
| 04.26 | It will then check the condition and repeat the loop while the condition is true. |
| 04.31 | The syntax for do-while loop is as follows - 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 |
| 04.51 | Open the Terminal and type;
|
| 04.55 | gedit doWhileLoop dot pl space ampersand
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| 05.03 | and then press Enter |
| 05.05 | This will open the doWhileLoop.pl file in gedit. |
| 05.09 | Type the following piece of code -
|
| 05.12 | hash exclamation mark slash u s r slash bin slash perl
|
| 05.20 | Press Enter
|
| 05.21 | dollar i equals to zero semicolon press enter |
| 05.28 | do space |
| 05.30 | open curly bracket enter type |
| 05.33 | print space double quote Value of i colon space dollar i slash n double quote complete semicolon |
| 05.47 | Press Enter
|
| 05.49 | dollar i plus plus semicolon 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 |
| 06.11
| Here is the detail explanation of a do-while loop. | |
| 06.14 | We have initialized the variable i to 0. |
| 06.19 | First time, the do-while loop will print the output as 'Value of i colon 0' on the terminal
|
| 06.26 | without checking for condition |
| 06.29 | $i++ will increment the value of variable i by one each time loop gets executed. |
| 06.37 | Second time, the condition $i less than or equal to 4 will be checked.
|
| 06.44 | If the condition is true, the loop will get executed again.
|
| 06.49 | In our case, second time the output displayed on terminal will be 'Value of I colon 1'. |
| 06.58 | The loop will get executed till the condition becomes false that is when variable i becomes 5. |
| 07.07 | 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 and press Enter. |
| 07.24 | The following line will be displayed on the terminal |
| 07.27 | doWhileLoop.pl syntax OK |
| 07.31 | As there are no compilation or syntax errors, we will now execute the Perl script.
|
| 07.36 | Type,perl doWhileLoop dot pl and press Enter |
| 07.44 | 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 and type -
|
| 07.56 | gedit loop dot pl space ampersand and press Enter |
| 08.03 | This will open loop dot pl file in gedit.
|
| 08.08 | Now type the piece of code shown. |
| 08.13 | We have declared a variable count and initialized it to zero |
| 08.20 | In the while loop condition, we are checking if the variable count is greater than zero.
|
| 08.30 | The condition is not true. So, the while loop code will not be executed even once. |
| 08..36 | Then the do...while loop, we are first executing the code and then checking the condition. |
| 08.45 | So, the code will be executed at least once. |
| 08.50 | 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. |
| 09.06 | Now, switch to terminal and type the following to check for any compilation or syntax errors
|
| 09.13 | perl hyphen c loop dot pl and press Enter. |
| 09.19 | The following line will be displayed on the terminal loop dot pl syntax OK |
| 09.27 | As there are no compilation or syntax errors, let us execute the Perl script. |
| 09.32 | By Typing
|
| 09.34 | perl loop dot pl and press Enter. |
| 09.39 | The following output will be displayed on the terminal.
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| 09.44 | I am in do-while loop |
| 09.47 | Here we can see, there is no output message displaying 'I am in while loop'
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| 09.52 | This message was what we printed inside the while loop. |
| 10.00 | This implies that,
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| 10.02 | do-while loop executes at-least once before evaluating the condition
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| 10.08 | whereas while loop does not get executed even once when the condition specified is false. |
| 10.16 | I hope the difference is clear to you now.
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| 10.19 | That's all there is to while and do-while loops. |
| 10.23 | Let us summarize. |
| 10.25 | In this tutorial, we have learnt - |
| 10.27 | while loop and do-while loop in Perl |
| 10.29 | using sample programs. |
| 10.32 | Here is assignment for you - |
| 10.34 | Print 'Hello Perl' till the count of variable reaches 10 |
| 10.39 | by using while loop and do-while loops |
| 10.42 | Watch the video available at the following link
|
| 10.46 | It summaries the Spoken Tutorial project
|
| 10.49 | If you do not have good bandwidth, you can download and watch it |
| 10.54 | The Spoken Tutorial Project Team
|
| 10.57 | 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.
|
| 11.25 | More information on this Mission is available spoken hypen tutorial dot org slash NMEICT hyphen Intro |
| 11.37 | Hope you enjoyed this Perl tutorial. |
| 11.39 | This is Amol signing off.Thanks for joining |
