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

• if-elsif-else statement and
• switch statement in Perl

I will also be using the gedit Text Editor.

You can use any text editor of your choice.

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.

• to test multiple conditions and
• When all conditions fail then it executes the default else block

if (condition) {

piece of code;

} elsif (condition) {

another piece of code;

} else {

code to be executed if both the above

conditions are false;

}

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

Highlight if (condition)

Highlight elsif (condition)

Highlight else

If not, then the else if condition is checked and executed if it is true.

Otherwise, the code within else block is executed.

gedit conditionalBlocks.pl &

and press Enter.

gedit conditionalBlocks dot pl space ampersand

and press Enter

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”;

}

Type the following piece of code as displayed on the screen.

perl conditionalBlocks.pl

Don't press Enter.

perl conditionalBlocks dot pl

1. I am skipping the compilation step. It is not a mandatory step for executing Perl scripts.
2. If there is any compilation error,

• execution will throw an error and
• will stop execution of script

Hi, I am Perl

Hi, I am Perl

Switch to gedit.

perl conditionalBlocks.pl

Type

perl conditionalBlocks dot pl

and press Enter.

Hi, I am Java

Hi, I am Java

perl conditionalBlocks.pl

Type

perl conditionalBlocks dot pl

and press Enter.

I am not a computer language

I am not a computer language

• Only one if block that satisfies the condition will be executed
• otherwise the default else block will be executed.

<<Don't read out the remaining part just display>>

if (condition) { code1; }

elsif (condition) { code2; }

elsif (condition) { code3; }

else { default_code;}

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.

Now let us learn about the switch statement.

After that, Switch module was introduced,

which provided the functionality of switch statement.

Modules in Perl will be covered in subsequent tutorials.

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}

}

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

gedit sampleSwitch.pl &

and press Enter.

gedit sampleSwitch dot pl space ampersand

and press Enter

$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”;}

}

We will learn about use keyword in detail in subsequent tutorials.

perl sampleSwitch.pl

perl sampleSwitch.pl

press Enter

Highlight the output on terminal

I am Perl

perl sampleSwitch.pl

perl sampleSwitch.pl

Press Enter

Highlight the output on terminal

I am Linux

Highlight case 'Java'

<Don't execute this part>

So the else statement will be executed.

perl sampleSwitch.pl

perl sampleSwitch.pl

Press Enter

Highlight the output on Highlight

I am not a computer language

• 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

Highlight else case

In such a scenario,

• if none of the cases match
• then there will be no output from the switch statement.

• Re-write the previous assignment
• given earlier in this tutorial
• using switch statement.

In this tutorial, we have learnt -

• if-elsif-else statement and
• switch statement in Perl
• using sample programs.

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This is Amol Brahmankar signing off.

Thanks for joining