Difference between revisions of "PERL/C2/More-Conditional-statements/English-timed"

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Revision as of 12:28, 28 May 2014

Visual Cue
Narration
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 spaceopen 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.

Contributors and Content Editors

Gaurav, PoojaMoolya, Sandhya.np14

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