Difference between revisions of "PERL/C2/More-Conditional-statements/English-timed"
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Revision as of 11:27, 13 June 2014
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| 00.00 | Welcome to the spoken tutorial on if-elsif-else and switch conditional statements in Perl. |
| 00.07 | In this tutorial, we will learn about |
| 00.10 | The if-elsif-else statement and switch statement in Perl |
| 00.15 | I am using Ubuntu Linux12.04 operating system and Perl 5.14.2
|
| 00.22 | I will also be using the gedit Text Editor.
|
| 00.25 | You can use any text editor of your choice. |
| 00.29 | You should have basic knowledge of Variables and Comments in Perl. |
| 00.34 | and knowledge of for, foreach, while and do-while loops and |
| 00.38 | if and if-else statements will be an added advantage. |
| 00.43 | Please go through the relevant spoken tutorials on the spoken tutorial website. |
| 00.48 | If-elsif-else statement in Perl can be used |
| 00.52 | to test multiple conditions and |
| 00.54 | When all conditions fail then it executes the default else block |
| 00.59 | The syntax of if-elsif-else statement is as follows |
| 01.04 | if space open bracket condition close bracket space Open curly bracket press Enter |
| 01.13 | piece of code to be executed when the condition is true semicolon
|
| 01.18 | Press Enter |
| 01.20 | Close curly bracket space elsif space open bracket condition close bracket space open curly bracket |
| 01.30 | Press Enter |
| 01.31 | another piece of code semicolon |
| 01.33 | to be executed when elsif condition is true |
| 01.37 | Press Enter |
| 01.39 | close curly bracket space else space open curly bracket
|
| 01.44 | Enter |
| 01.45 | code semicolon to be executed when both the above conditions are false semicolon |
| 01.51 | Press Enter |
| 01.52 | close curly bracket |
| 01.55 | First, the if condition is checked and executed if the condition is true. |
| 02.01 | If not, then the else if condition is checked and executed if it is true. |
| 02.06 | Otherwise, the code within else block is executed. |
| 02.11 | Now let us look at an example of if-elsif-else statement. |
| 02.16 | Open the Terminal and type |
| 02.19 | gedit conditionalBlocks dot pl space ampersand
|
| 02.26 | and press Enter |
| 02.28 | This will open the conditionalBlocks.pl file in gedit. |
| 02.33 | Type the following piece of code as displayed on the screen. |
| 02.38 | We have assigned the value 'Perl' to variable language. |
| 02.44 | Note that, eq is string comparison operator. |
| 02.49 | And then we have the various conditons that we want to check. |
| 02.55 | Now, press ctrl+s to save the file.
|
| 02.58 | Then switch to terminal and execute file directly. |
| 03.02 | Type, perl conditionalBlocks dot pl
|
| 03.09 | Note: I am skipping the compilation step. It is not a mandatory step for executing Perl scripts. |
| 03.16 | If there is any compilation error, |
| 03.18 | execution will throw an error and will stop execution of script
|
| 03.23 | Now press Enter.
|
| 03.25 | The output shown on the terminal is |
| 03.27 | Hi, I am Perl |
| 03.29 | Now, let us look at our next case. |
| 03.31 | Switch to gedit. |
| 03.33 | Assign 'Java' to variable language as shown. |
| 03.37 | Press ctrl+s to save the file. |
| 03.40 | Switch to the terminal and execute the file.
|
| 03.43 | Type perl conditionalBlocks dot pl
|
| 03.50 | and press Enter. |
| 03.53 | The output shown on terminal is Hi, I am Java |
| 03.59 | Again let us switch back to gedit. |
| 04.03 | Now, let us assign 'English' to the language variable. |
| 04.07 | Press ctrl+s to save the file.
|
| 04.09 | Switch to the terminal and execute the file.
|
| 04.13 | Type perl conditionalBlocks dot pl
|
| 04.18 | and press Enter. |
| 04.19 | The output shown on terminal is |
| 04.22 | I am not a computer language |
| 04.27 | The 3 cases imply that; |
| 04.29 | Only one if block that satisfies the condition will be executed. |
| 04.35 | otherwise the default else block will get execute. |
| 04.39 | We can have multiple elsif conditions as per our requirement, like this. |
| 04.46 | Here is an assignment for you - |
| 04.48 | Write an if-elsif-else statement to print |
| 04.51 | “I am a Science graduate” if stream is science |
| 04.55 | “I am a Commerce graduate” if stream is commerce
|
| 04.59 | “I am an Arts graduate” if stream is neither science or commerce
|
| 05.06 | Now let us learn about the switch statement.
|
| 05.10 | Till Perl 5.8, there was no switch statement in Perl. |
| 05.14 | After that, Switch module was introduced, |
| 05.18 | which provided the functionality of switch statement. |
| 05.22 | Note: Modules in Perl will be covered in subsequent tutorials. |
| 05.27 | The syntax of switch is as follows: |
| 05.30 | use Switch semicolon |
| 05.32 | Press Enter |
| 05.34 | switch space open bracket dollar value close bracket space open curly bracket |
| 05.42 | Press Enter |
| 05.44 | case space 1 space open curly bracket executes when dollar value equal to 1 close curly bracket. |
| 05.53 | Press Enter |
| 05.55 | case space single quote a single quote space open curly bracket executes when dollar value equal to single quote a single quote close curly bracket |
| 06.09 | Press Enter
|
| 06.10 | else space open curly bracket executes when dollar value does not match any of the cases |
| 06.18 | Close curly bracket |
| 06.19 | Press Enter
|
| 06.20 | close curly bracket |
| 06.22 | Let us understand switch using a sample program. |
| 06.26 | Open the Terminal and type |
| 06.29 | gedit sampleSwitch dot pl space ampersand |
| 06.36 | and press Enter |
| 06.38 | Now, type the sample program as shown on the screen. |
| 06.43 | Let us understand how the switch statement works. |
| 06.46 | The use Switch statement includes the Switch module inside the Perl code. |
| 06.54 | Note: We will learn about use keyword in detail in subsequent tutorials. |
| 07.00 | Now we'll test the different cases. |
| 07.03 | We have assigned 'Perl' to the variable $var |
| 07.08 | The value in variable $var is checked in the switch statement. |
| 07.14 | In the first case, it matches with the case 'Perl'. |
| 07.19 | So the code written against this case will be executed. |
| 07.24 | Press ctrl+s to save the file. |
| 07.27 | Now, switch to terminal and execute the script |
| 07.31 | perl sampleSwitch.pl |
| 07.36 | press Enter |
| 07.38 | The following output is shown on the terminal |
| 07.41 | I am Perl
|
| 07.43 | Switch back to sampleSwitch.pl in gedit. |
| 07.48 | Now, let us assign 'Linux' to the variable $var |
| 07.52 | Press Ctrl S to save the file. |
| 07.57 | Again, the value of variable $var will be checked in switch. |
| 08.03 | It matches with the case 'Linux' |
| 08.05 | So code written against this case will get executed. |
| 08.10 | Now, switch to terminal and execute the script |
| 08.15 | perl sampleSwitch.pl |
| 08.19 | Press Enter |
| 08.21 | The following output is shown on the terminal |
| 08.24 | I am Linux
|
| 08.26 | Switch to sampleSwitch.pl in gedit. |
| 08.30 | Similarly, if variable $var has value 'Java' , then second case will be checked. |
| 08.38 | Now, let us assign 'English' to the variable $var |
| 08.42 | Again, the value of variable $var will be checked in switch. |
| 08.47 | It does not match any of the case statements. |
| 08.50 | So the else statement will be executed. |
| 08.54 | Now, switch to terminal and execute the script |
| 09.00 | perl sampleSwitch.pl |
| 09.07 | and Press Enter |
| 09.09 | The following output is shown on the terminal - |
| 09.12 | I am not a computer language
|
| 09.17 | The 3 cases imply that: |
| 09.20 | The value of the expression decides the case to be executed |
| 09.25 | Only the valid case will be executed and |
| 09.28 | When there is no valid case, then the default else case will be executed |
| 09.35 | It is not mandatory to write the else case. |
| 09.39 | In such a scenario, |
| 09.41 | if none of the cases match |
| 09.44 | then there will be no output from the switch statement. |
| 09.48 | Here is another assignment for you - |
| 09.50 | Re-write the previous assignment |
| 09.53 | given earlier in this tutorial using switch statement.
|
| 09.57 | Let us summarize. |
| 09.59 | In this tutorial, we have learnt -
|
| 10.01 | if-elsif-else statement and
|
| 10.04 | switch statement in Perl |
| 10.05 | using sample programs. |
| 10.08 | Watch the video available at the following link
|
| 10.12 | It summaries the Spoken Tutorial project
|
| 10.15 | If you do not have good bandwidth, you can download and watch it |
| 10.20 | The Spoken Tutorial Project Team Conducts workshops using spoken tutorials
|
| 10.25 | Gives certificates to those who pass an online test
|
| 10.30 | For more details, please write to contact at spoken hyphen tutorial dot org |
| 10.36 | Spoken Tutorial Project is a part of the Talk to a Teacher project
|
| 10.40 | It is supported by the National Mission on Education through ICT, MHRD, Government of India.
|
| 10.47 | More information on this Mission is available at spoken hyphen tutorial dot org slash NMEICT hyphen Intro |
| 10.58 | Hope you enjoyed this Perl tutorial. |
| 11.00 | This is Amol signing off.
|
| 11.03 | Thanks for joining. |
