PERL/C2/More-Conditional-statements/English

Title Of Script: if-elsif-else, switch statement

Author: Amol Brahmankar

Keywords: Conditional Statements in Perl, if-elsif-else, switch statement in perl video tutorial.

Visual Cue	Narration
Slide	Welcome to the spoken tutorial on if-elsif-else and switch conditional statements in Perl.
Slide: Learning Objectives	In this tutorial, we will learn about the if-elsif-else statement and switch statement in Perl
Slide: System Requirements	I am using Ubuntu Linux12.04 operating system and Perl 5.14.2 I will also be using the gedit Text Editor. You can use any text editor of your choice.
Slide: Prerequisites	You should have basic knowledge of Variables and Comments in Perl and knowledge of for, foreach, while and do-while loops and if and if-else statements will be an added advantage. Please go through relevant spoken tutorials on the spoken tutorial website.
Slide	If-elsif-else statement in Perl can be used to test multiple conditions and When all conditions fail then it executes the default else block
Slide if (condition) { piece of code; } elsif (condition) { another piece of code; } else { code to be executed if both the above conditions are false; }	The syntax of if-elsif-else statement is as follows if space open bracket condition close bracket space Open curly bracket Press Enter piece of code semicolon to be executed when the condition is true Press Enter Close curly bracket space elsif space open bracket condition close bracket space open curly bracket Press Enter another piece of code semicolon to be executed when elsif condition is true Press Enter close curly bracket space else space open curly bracket Enter code to be executed when both the above conditions are false semicolon Press Enter close curly bracket
Slide Highlight if (condition) Highlight elsif (condition) Highlight else	First, the if condition is checked and executed if the condition is true. If not, then the else if condition is checked and executed if it is true. Otherwise, the code within else block is executed.
	Now let us look at an example of if-elsif-else statement.
Switch to the Terminal and type gedit conditionalBlocks.pl & and press Enter.	Open the Terminal and type gedit conditionalBlocks dot pl space ampersand and press Enter
Point to the filename conditionalBlocks.pl in the Titlebar of gedit. Type the piece of code. #!/usr/bin/perl $language = 'Perl'; if ($language eq 'Perl') { print “Hi, I am Perl\n”; } elsif ($ language eq 'Java') { print “Hi, I am Java\n”; } else { print “I am not a computer language\n”; }	This will open the conditionalBlocks.pl file in gedit. Type the following piece of code as displayed on the screen.
Highlight variables declaration	We have assigned the value 'Perl' to variable language.
Highlight eq	Note that, eq is the string comparison operator.
Highlight the if-elsif-else code	And then we have the various conditons that we want to check here.
Press Ctrl S	Now, press ctrl+s to save the file.
Switch to terminal	Then switch to the terminal and execute file directly.
Type perl conditionalBlocks.pl Don't press Enter.	Type, perl conditionalBlocks dot pl
	Note: I am skipping the compilation step. It is not a mandatory step for executing Perl scripts. If there is any compilation error, execution will throw an error and will stop execution of script
Press Enter.	Now press Enter.
Highlight the output on the terminal Hi, I am Perl	The output shown on the terminal is Hi, I am Perl
Switch to gedit	Now, let us look at our next case. Switch to gedit.
Change $language = 'Java';	Assign 'Java' to variable language as shown.
Press Ctrl S	Press ctrl+s to save the file.
Switch to terminal perl conditionalBlocks.pl	Switch to the terminal and execute the file. Type perl conditionalBlocks dot pl and press Enter.
Highlight the output on the terminal Hi, I am Java	The output shown on terminal is Hi, I am Java
Switch to gedit	Again let us switch back to gedit.
Change $language = 'English';	Now, let us assign 'English' to the language variable.
Press Ctrl S	Again, press ctrl+s to save the file.
Switch to terminal perl conditionalBlocks.pl	Switch to the terminal and execute the file. Type perl conditionalBlocks dot pl and press Enter.
Highlight the output on the terminal I am not a computer language	The output shown on terminal is I am not a computer language
Slide	The 3 cases imply that; Only one if block that satisfies the condition will be executed otherwise the default else block will be executed.
Slide	We can have multiple elsif conditions as per our requirement, like this. <<Don't read out the remaining part just display>> if (condition) { code1; } elsif (condition) { code2; } elsif (condition) { code3; } else { default_code;}
Slide: Assignment	Here is an assignment for you - Write an if-elsif-else statement to print “I am a Science graduate” if stream is science “I am a Commerce graduate” if stream is commerce “I am an Arts graduate” if stream is neither science or commerce.
	<<Pause>> Now let us learn about the switch statement.
Slide	Till Perl 5.8, there was no switch statement in Perl. After that, Switch module was introduced, which provided the functionality of switch statement.
Remain on previous slide	Note: Modules in Perl will be covered in subsequent tutorials.
use Switch; switch ($value) { case 1 { executes when $value = 1} case 'a' { executes when $value = 'a'} else { executes when $value does not match any of the cases} }	The syntax of switch is as follows: use Switch semicolon Press Enter switch space open bracket dollar value close bracket space open curly bracket Press Enter case space 1 space open curly bracket executes when dollar value equal to 1 close curly bracket. Press Enter 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 Press Enter else space open curly bracket executes when dollar value does not match any of the cases close curly bracket Press Enter close curly bracket
	Let us understand switch using a sample program.
Switch to the Terminal and type gedit sampleSwitch.pl & and press Enter.	Open the Terminal and type gedit sampleSwitch dot pl space ampersand and press Enter
use Switch; $var = 'Perl' switch ($var) { case 'Perl' {print “I am Perl\n”;} case 'Java' {print “I am Java\n”;} case 'Linux' {prin “I am Linux\n”;} else {print “I am not a computer language\n”;} }	Now, type the sample program as shown on the screen.
Gedit	Let us understand how the switch statement works.
Highlight use Switch	The use Switch statement includes the Switch module inside the Perl code.
	Note: We will learn about use keyword in detail in subsequent tutorials.
	Now we'll test the different cases.
Highlight $var = 'Perl'	We have assigned 'Perl' to the variable $var
Highlight switch ($var)	The value in variable $var is checked in the switch statement.
Highlight case 'Perl'	In the first case, it matches with the case 'Perl'.
Highlight {print “I am Perl\n”;}	So the code written against this case will be executed.
Press ctrl+s	Press ctrl+s to save the file.
Switch to terminal perl sampleSwitch.pl	Now, switch to terminal and execute the script perl sampleSwitch.pl press Enter
Terminal Highlight the output on terminal	The following output is shown on the terminal I am Perl
	Switch back to sampleSwitch.pl in gedit.
Change $var = 'Linux'	Now, let us assign 'Linux' to the variable $var
Highlight switch ($var)	Again, the value of variable $var will be checked in switch.
Highlight case 'Linux'	It matches with the case 'Linux'
Highlight {print “I am Linux\n”;}	So code written against this case will get executed.
Switch to terminal perl sampleSwitch.pl	Now, switch to terminal and execute the script perl sampleSwitch.pl Press Enter
Terminal Highlight the output on terminal	The following output is shown on the terminal I am Linux
Switch to gedit.	Switch to sampleSwitch.pl in gedit.
Change $var = ''Java'' >> Highlight case 'Java' <Don't execute this part>	Similarly, if variable $var has value 'Java', then second case will be checked.
Change $var = 'English'	Now, let us assign 'English' to the variable $var
Highlight switch ($var)	Again, the value of variable $var will be checked in switch.
Point to the 3 case statements >> then point to the else statement	It does not match any of the case statements. So the else statement will be executed.
Switch to Highlight perl sampleSwitch.pl	Now, switch to terminal and execute the script perl sampleSwitch.pl Press Enter
Terminal Highlight the output on Highlight	The following output is shown on the terminal - I am not a computer language
Slide	The 3 cases imply that: The value of the expression decides the case to be executed Only the valid case will be executed and When there is no valid case, then the default else case will be executed
Slide Highlight else case	It is not mandatory to write the else case. In such a scenario, if none of the cases match then there will be no output from the switch statement.
Slide: Assignment	Here is another assignment for you - Re-write the previous assignment given earlier in this tutorial using switch statement.
Slide: Summary	Let us summarize. In this tutorial, we have learnt - if-elsif-else statement and switch statement in Perl using sample programs.
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Acknowledgment http://spoken-tutorial.org\NMEICT-Intro	Spoken Tutorial Project is a part of the Talk to a Teacher project It is supported by the National Mission on Education through ICT, MHRD, Government of India. More information on this Mission is available spoken hypen tutorial dot org slash NMEICT hyphen Intro
	Hope you enjoyed this Perl tutorial. This is Amol Brahmankar signing off. Thanks for joining

Contributors and Content Editors

AmolBrahmankar, PoojaMoolya