Difference between revisions of "PERL/C2/while-do-while-loops/English-timed"
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! <center>'''Narration'''</center> | ! <center>'''Narration'''</center> | ||
Revision as of 11:26, 13 June 2014
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| 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. |
