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

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|-

|-

|Welcome to the spoken tutorial on ''' if-elsif-else ''' and '''switch''' conditional statements in Perl.

|Welcome to the spoken tutorial on ''' if-elsif-else ''' and '''switch''' conditional statements in Perl.

   

   

|-

|-

| In this tutorial, we will learn about  

| In this tutorial, we will learn about  

|-

|-

  |The ''' if-elsif-else''' statement and ''' switch''' statement in '''Perl '''

  |The ''' if-elsif-else''' statement and ''' switch''' statement in '''Perl '''

   

   

|-

|-

| I am using '''Ubuntu Linux12.04''' operating system and '''Perl 5.14.2'''

| I am using '''Ubuntu Linux12.04''' operating system and '''Perl 5.14.2'''

   

   

   

   

|-

|-

|I will also be using the '''gedit '''Text Editor.

|I will also be using the '''gedit '''Text Editor.

   

   

   

   

|-

|-

|You can use any text editor of your choice.

|You can use any text editor of your choice.

   

   

|-

|-

| You should have basic knowledge of '''Variables '''and''' Comments '''in''' Perl.'''

| You should have basic knowledge of '''Variables '''and''' Comments '''in''' Perl.'''

   

   

|-

|-

|and knowledge of ''' for, foreach, while''' and '''do-while''' loops and  

|and knowledge of ''' for, foreach, while''' and '''do-while''' loops and  

|-

|-

| ''' if ''' and '''if-else''' statements will be an added advantage.

| ''' if ''' and '''if-else''' statements will be an added advantage.

|-

|-

|Please go through the relevant spoken tutorials on the '''spoken tutorial '''website.

|Please go through the relevant spoken tutorials on the '''spoken tutorial '''website.

   

   

|-

|-

|''' If-elsif-else''' statement in '''Perl''' can be used  

|''' If-elsif-else''' statement in '''Perl''' can be used  

   

   

|-

|-

| to test multiple conditions and  

| to test multiple conditions and  

   

   

|-

|-

|When all conditions fail then it executes the default '''else''' block  

|When all conditions fail then it executes the default '''else''' block  

   

   

|-

|-

|The syntax of '''if-elsif-else''' statement is as follows  

|The syntax of '''if-elsif-else''' statement is as follows  

   

   

|-

|-

|''' if space''' open bracket ''' condition''' close bracket space Open curly bracket press Enter

|''' if space''' open bracket ''' condition''' close bracket space Open curly bracket press Enter

   

   

|-

|-

|piece of code  to be executed when the condition is true semicolon

|piece of code  to be executed when the condition is true semicolon

   

   

|-

|-

|Press '''Enter '''

|Press '''Enter '''

|-

|-

| Close curly bracket space '''elsif''' space open bracket ''' condition''' close bracket space open curly bracket  

| Close curly bracket space '''elsif''' space open bracket ''' condition''' close bracket space open curly bracket  

|-

|-

|Press '''Enter '''

|Press '''Enter '''

|-

|-

|another piece of code semicolon  

|another piece of code semicolon  

   

   

|-

|-

|to be executed when '''elsif condition''' is true  

|to be executed when '''elsif condition''' is true  

   

   

|-

|-

|Press '''Enter '''

|Press '''Enter '''

   

   

|-

|-

|close curly bracket space  ''' else'''  space open curly bracket  

|close curly bracket space  ''' else'''  space open curly bracket  

   

   

|-

|-

| Enter  

| Enter  

   

   

|-

|-

|code semicolon  to be executed when both the above conditions are false  semicolon

|code semicolon  to be executed when both the above conditions are false  semicolon

|-

|-

|Press '''Enter '''

|Press '''Enter '''

   

   

|-

|-

| close curly bracket  

| close curly bracket  

|-

|-

| First, the ''' if ''' condition is checked and executed if the condition is true.  

| 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.  

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

   

   

|-

|-

|Otherwise, the code within '''else''' block is executed.  

|Otherwise, the code within '''else''' block is executed.  

   

   

|-

|-

|Now let us look at an example of '''if-elsif-else''' statement.  

|Now let us look at an example of '''if-elsif-else''' statement.  

   

   

|-

|-

|Open the Terminal and type  

|Open the Terminal and type  

   

   

|-

|-

| '''gedit conditionalBlocks dot pl space ampersand'''

| '''gedit conditionalBlocks dot pl space ampersand'''

   

   

   

   

|-

|-

| and press '''Enter'''

| and press '''Enter'''

   

   

|-

|-

|This will open the ''' conditionalBlocks.pl''' file in '''gedit. '''

|This will open the ''' conditionalBlocks.pl''' file in '''gedit. '''

   

   

|-

|-

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

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

   

   

|-

|-

| We have assigned the value  ''' 'Perl' ''' to variable language.

| We have assigned the value  ''' 'Perl' ''' to variable language.

|-

|-

|Note that, '''eq''' is  '''string comparison''' operator.  

|Note that, '''eq''' is  '''string comparison''' operator.  

   

   

|-

|-

|  And then we have the various conditons that we want to check.

|  And then we have the various conditons that we want to check.

   

   

|-

|-

|Now, press ctrl+s to save the file.  

|Now, press ctrl+s to save the file.  

   

   

   

   

|-

|-

|Then switch to terminal and execute file directly.  

|Then switch to terminal and execute file directly.  

   

   

|-

|-

|  Type, '''perl conditionalBlocks dot pl '''

|  Type, '''perl conditionalBlocks dot pl '''

   

   

|-

|-

|Note: I am skipping the compilation step. It is not a mandatory step for executing Perl scripts.  

|Note: I am skipping the compilation step. It is not a mandatory step for executing Perl scripts.  

   

   

|-

|-

| If there is any compilation error,  

| If there is any compilation error,  

   

   

|-

|-

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

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

   

   

|-

|-

| Now press '''Enter.'''

| Now press '''Enter.'''

   

   

   

   

|-

|-

|The output shown on the terminal is  

|The output shown on the terminal is  

   

   

|-

|-

|  ''' Hi, I am Perl '''

|  ''' Hi, I am Perl '''

   

   

|-

|-

| Now, let us look at our next case.  

| Now, let us look at our next case.  

   

   

|-

|-

|Switch to '''gedit. '''

|Switch to '''gedit. '''

   

   

|-

|-

|Assign ''' 'Java' ''' to variable language as shown.  

|Assign ''' 'Java' ''' to variable language as shown.  

   

   

|-

|-

|  Press '''ctrl+s''' to save the file.  

|  Press '''ctrl+s''' to save the file.  

   

   

|-

|-

|Switch to the terminal and execute the file.  

|Switch to the terminal and execute the file.  

   

   

   

   

|-

|-

|Type ''' perl conditionalBlocks dot pl '''

|Type ''' perl conditionalBlocks dot pl '''

   

   

|-

|-

| and press '''Enter.'''

| and press '''Enter.'''

   

   

|-

|-

|  The output shown on terminal is ''' Hi, I am Java '''

|  The output shown on terminal is ''' Hi, I am Java '''

   

   

|-

|-

| Again let us switch back to '''gedit. '''

| Again let us switch back to '''gedit. '''

   

   

|-

|-

| Now, let us assign  ''' 'English' ''' to the ''' language''' variable.  

| Now, let us assign  ''' 'English' ''' to the ''' language''' variable.  

|-

|-

| Press ''' ctrl+s ''' to save the file.  

| Press ''' ctrl+s ''' to save the file.  

   

   

|-

|-

|Switch to the terminal and execute the file.  

|Switch to the terminal and execute the file.  

   

   

   

   

|-

|-

|Type '''perl conditionalBlocks dot pl '''

|Type '''perl conditionalBlocks dot pl '''

   

   

|-

|-

|and press '''Enter.'''

|and press '''Enter.'''

   

   

|-

|-

|The output shown on terminal is  

|The output shown on terminal is  

|-

|-

|'''I am not a computer language '''

|'''I am not a computer language '''

   

   

|-

|-

|  The 3 cases imply that;  

|  The 3 cases imply that;  

|-

|-

| Only one ''' if block''' that satisfies the condition will be executed.

| Only one ''' if block''' that satisfies the condition will be executed.

   

   

|-

|-

| otherwise the default ''' else block''' will get execute.  

| otherwise the default ''' else block''' will get execute.  

|-

|-

|We can have multiple ''' elsif''' conditions as per our requirement, like this.  

|We can have multiple ''' elsif''' conditions as per our requirement, like this.  

   

   

|-

|-

|Here is an assignment for you -  

|Here is an assignment for you -  

   

   

|-

|-

|Write an ''' if-elsif-else''' statement to print   

|Write an ''' if-elsif-else''' statement to print   

   

   

|-

|-

|''' “I am a Science graduate” ''' if '''stream''' is ''' science '''

|''' “I am a Science graduate” ''' if '''stream''' is ''' science '''

|-

|-

|'''“I am a Commerce graduate” ''' if '''stream''' is '''commerce'''  

|'''“I am a Commerce graduate” ''' if '''stream''' is '''commerce'''  

   

   

   

   

|-

|-

|''' “I am an Arts graduate” ''' if ''' stream''' is neither ''' science''' or '''commerce '''

|''' “I am an Arts graduate” ''' if ''' stream''' is neither ''' science''' or '''commerce '''

   

   

   

   

|-

|-

|Now let us learn about the '''switch''' statement.  

|Now let us learn about the '''switch''' statement.  

   

   

|-

|-

| Till Perl 5.8, there was no '''switch''' statement in '''Perl.'''  

| Till Perl 5.8, there was no '''switch''' statement in '''Perl.'''  

   

   

|-

|-

| After that, '''Switch module''' was introduced,  

| After that, '''Switch module''' was introduced,  

   

   

|-

|-

|which provided the functionality of ''' switch''' statement.  

|which provided the functionality of ''' switch''' statement.  

   

   

|-

|-

| Note: ''' Modules''' in '''Perl''' will be covered in subsequent tutorials.  

| Note: ''' Modules''' in '''Perl''' will be covered in subsequent tutorials.  

|-

|-

| The syntax of ''' switch''' is as follows:  

| The syntax of ''' switch''' is as follows:  

   

   

|-

|-

|  use '''Switch''' semicolon

|  use '''Switch''' semicolon

|-

|-

| Press '''Enter'''  

| Press '''Enter'''  

|-

|-

| '''switch ''' space open bracket '''dollar value''' close bracket space open curly bracket  

| '''switch ''' space open bracket '''dollar value''' close bracket space open curly bracket  

|-

|-

|Press '''Enter '''

|Press '''Enter '''

   

   

|-

|-

|  '''case ''' space 1 space open curly bracket ''' executes when dollar value equal to 1''' close curly bracket.  

|  '''case ''' space 1 space open curly bracket ''' executes when dollar value equal to 1''' close curly bracket.  

   

   

|-

|-

| Press '''Enter'''  

| 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  

|'''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 '''

| Press ''' Enter '''

   

   

|-

|-

|''' else''' space open curly bracket ''' executes when dollar value does not match any of the cases '''

|''' else''' space open curly bracket ''' executes when dollar value does not match any of the cases '''

   

   

|-

|-

|Close curly bracket  

|Close curly bracket  

|-

|-

|Press '''Enter '''

|Press '''Enter '''

   

   

|-

|-

|  close curly bracket  

|  close curly bracket  

|-

|-

| Let us understand '''switch''' using a sample program.  

| Let us understand '''switch''' using a sample program.  

   

   

|-

|-

|  Open the Terminal and type  

|  Open the Terminal and type  

   

   

|-

|-

| ''' gedit sampleSwitch dot pl space ampersand'''

| ''' gedit sampleSwitch dot pl space ampersand'''

   

   

|-

|-

|and press '''Enter'''

|and press '''Enter'''

   

   

|-

|-

   |Now, type the sample program as shown on the screen.  

   |Now, type the sample program as shown on the screen.  

 

 

|-

|-

|  Let us understand how the ''' switch''' statement works.  

|  Let us understand how the ''' switch''' statement works.  

   

   

|-

|-

| The '''use Switch''' statement includes the '''Switch''' module inside the '''Perl''' code.  

| The '''use Switch''' statement includes the '''Switch''' module inside the '''Perl''' code.  

|-

|-

| Note: We will learn about '''use keyword''' in detail in subsequent tutorials.  

| Note: We will learn about '''use keyword''' in detail in subsequent tutorials.  

|-

|-

| Now we'll test the different cases.   

| Now we'll test the different cases.   

|-

|-

| We have assigned ''' 'Perl' ''' to the variable ''' $var'''

| We have assigned ''' 'Perl' ''' to the variable ''' $var'''

   

   

|-

|-

| The value in variable ''' $var''' is checked in the switch statement.  

| The value in variable ''' $var''' is checked in the switch statement.  

|-

|-

| In the first case, it matches with the case ''' 'Perl'.'''  

| In the first case, it matches with the case ''' 'Perl'.'''  

|-

|-

| So the code written against this '''case''' will be executed.  

| So the code written against this '''case''' will be executed.  

|-

|-

| Press ''' ctrl+s''' to '''save''' the file.  

| Press ''' ctrl+s''' to '''save''' the file.  

|-

|-

| Now, switch to terminal and execute the script  

| Now, switch to terminal and execute the script  

|-

|-

| '''perl sampleSwitch.pl'''

| '''perl sampleSwitch.pl'''

|-

|-

| press '''Enter'''  

| press '''Enter'''  

|-

|-

| The following output is shown on the terminal

| The following output is shown on the terminal

|-

|-

|''' I am Perl '''

|''' I am Perl '''

|-

|-

| Switch back to ''' sampleSwitch.pl''' in '''gedit.'''  

| Switch back to ''' sampleSwitch.pl''' in '''gedit.'''  

|-

|-

| Now, let us assign  ''' 'Linux' ''' to the variable ''' $var '''

| Now, let us assign  ''' 'Linux' ''' to the variable ''' $var '''

|-

|-

|Press ''' Ctrl S''' to save the file.

|Press ''' Ctrl S''' to save the file.

|-

|-

| Again, the value of variable ''' $var''' will be checked in switch.  

| Again, the value of variable ''' $var''' will be checked in switch.  

|-

|-

| It matches with the case  ''' 'Linux' '''

| It matches with the case  ''' 'Linux' '''

|-

|-

| So code written against this case will get executed.  

| So code written against this case will get executed.  

|-

|-

| Now, switch to terminal and execute the script  

| Now, switch to terminal and execute the script  

|-

|-

| '''perl sampleSwitch.pl'''

| '''perl sampleSwitch.pl'''

|-

|-

| Press '''Enter'''

| Press '''Enter'''

|-

|-

| The following output is shown on the terminal  

| The following output is shown on the terminal  

|-

|-

| ''' I am Linux'''  

| ''' I am Linux'''  

|-

|-

| Switch to ''' sampleSwitch.pl''' in ''' gedit.'''  

| Switch to ''' sampleSwitch.pl''' in ''' gedit.'''  

|-

|-

| Similarly, if variable ''' $var''' has value ''' 'Java' ''', then second case will be checked.  

| Similarly, if variable ''' $var''' has value ''' 'Java' ''', then second case will be checked.  

|-

|-

| Now, let us assign  ''' 'English' ''' to the variable ''' $var'''

| Now, let us assign  ''' 'English' ''' to the variable ''' $var'''

|-

|-

| Again, the value of variable ''' $var ''' will be checked in switch.  

| Again, the value of variable ''' $var ''' will be checked in switch.  

|-

|-

|It does not match any of the  ''' case''' statements.  

|It does not match any of the  ''' case''' statements.  

|-

|-

| So the ''' else ''' statement will be executed.  

| So the ''' else ''' statement will be executed.  

|-

|-

| Now, switch to terminal and execute the script  

| Now, switch to terminal and execute the script  

|-

|-

| ''' perl sampleSwitch.pl'''

| ''' perl sampleSwitch.pl'''

|-

|-

| and Press ''' Enter'''

| and Press ''' Enter'''

|-

|-

| The following output is shown on the terminal -  

| The following output is shown on the terminal -  

|-

|-

|''' I am not a computer language '''

|''' I am not a computer language '''

|-

|-

| The 3 cases imply that:  

| The 3 cases imply that:  

|-

|-

| The value of the expression decides the ''' case ''' to be executed  

| The value of the expression decides the ''' case ''' to be executed  

|-

|-

| Only the valid ''' case''' will be executed and  

| Only the valid ''' case''' will be executed and  

|-

|-

| When there is no valid '''case''', then the default ''' else '''  case will be executed  

| When there is no valid '''case''', then the default ''' else '''  case will be executed  

|-

|-

| It is not mandatory to write the '''else case. '''

| It is not mandatory to write the '''else case. '''

|-

|-

| In such a scenario,  

| In such a scenario,  

|-

|-

| if none of the ''' cases''' match  

| if none of the ''' cases''' match  

|-

|-

| then there will be no output from the ''' switch''' statement.  

| then there will be no output from the ''' switch''' statement.  

|-

|-

| Here is another assignment for you -  

| Here is another assignment for you -  

|-

|-

| Re-write the previous assignment  

| Re-write the previous assignment  

|-

|-

| given earlier in this tutorial using ''' switch''' statement.  

| given earlier in this tutorial using ''' switch''' statement.  

|-

|-

| Let us summarize.  

| Let us summarize.  

|-

|-

| In this tutorial, we have learnt -  

| In this tutorial, we have learnt -  

|-

|-

| ''' if-elsif-else''' statement and  

| ''' if-elsif-else''' statement and  

|-

|-

| '''switch''' statement in '''Perl '''

| '''switch''' statement in '''Perl '''

|-

|-

| '''using sample programs. '''

| '''using sample programs. '''

|-

|-

|Watch the video available at the following link

|Watch the video available at the following link

   

   

   

   

|-

|-

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|It summaries the Spoken Tutorial project

   

   

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|-

|If you do not have good bandwidth, you can download and watch it

|If you do not have good bandwidth, you can download and watch it

   

   

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|-

|  The Spoken Tutorial Project Team  Conducts workshops using spoken tutorials

|  The Spoken Tutorial Project Team  Conducts workshops using spoken tutorials

   

   

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|-

|Gives certificates to those who pass an online  test

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|For more details, please write to contact at spoken hyphen tutorial dot org

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|-

|  Spoken Tutorial Project is a part of the Talk to a  Teacher project

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|-

|More information on this Mission is available at spoken hyphen tutorial dot org slash NMEICT hyphen Intro

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|-

|-

|  Hope you enjoyed this Perl tutorial.  

|  Hope you enjoyed this Perl tutorial.  

   

   

|-

|-

|This is Amol signing off.

|This is Amol signing off.

   

   

|-

|-

|Thanks for joining.

|Thanks for joining.

   

   

|}

|}