Difference between revisions of "PERL/C2/while-do-while-loops/English-timed"

|'''Time'''

|'''Narration'''

| 00:01

|Welcome to the '''spoken tutorial''' on '''while and do-while loops''' in '''Perl'''.

| 00:06

| In this tutorial, we will learn about:

|00:09

| '''while''' loop in '''Perl'''  

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| '''do-while''' loop in '''Perl '''.  I am using '''Ubuntu Linux 12.04''' operating system and '''Perl 5.14.2'''.

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

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| 00:28

| You should have basic knowledge of '''variables''' and '''comments''' in ''' Perl.'''

|00:33

|Knowledge of '''for''' and '''foreach''' loops in '''Perl''' will be an added advantage.

|00:38

|Please go through the relevant spoken tutorials on the "Spoken Tutorial" website.  

| 00:43

| '''while''' loop in '''Perl''':

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|The '''while''' loop executes a block of code while a condition is true.  

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|The syntax of '''while''' loop is as follows -  

|00:53

|'''while''' space open bracket '''condition''' close bracket  

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|piece of code to be executed while the condition is true  

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|close curly bracket.  

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| So, what happens if the condition is not satisfied? Then the '''while''' loop will exit without executing the code within, even once.  

|01:16

|Now let us look at an example of '''while''' loop.  

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|Open the Terminal and type:

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|'''gedit whileLoop dot pl space ampersand'''

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|and press '''Enter'''.

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

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| Now type the following code:

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| '''hash exclamation mark slash u s r slash bin slash perl'''

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|press '''Enter'''.

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| 'dollar i' ($i) equals to zero semicolon

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| press '''Enter '''.

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|'''while''' open bracket '''dollar i less than or equal to four''' close bracket space  

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|open curly bracket press '''Enter''' and type:

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|'''print''' space double quote '''Value of i''' colon ''' dollar i backslash n''' double quote complete semicolon

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|press '''Enter'''.

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| '''dollar i plus plus semicolon'''

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| press '''Enter'''  and close the curly bracket.

|02:31

|Let me explain the '''while''' loop in detail.  

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| We have initialized the variable 'i' to 0.  

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|Now, we have specified the condition for '''while''' loop as '''$i''' less than or equal to 4.  

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| If the 'condition' is true, the code within the '''while''' loop will get executed.  

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|This means, first time our '''while''' loop will print "Value of i: 0" on the terminal.  

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|Then the '''$i++''' will increment the value of variable 'i' by one.  

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|Now again, the loop condition ''' $i<=4''' will be evaluated.  

|03:16

|And the loop will exit once the value of 'i' becomes 5.  

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| In this case, '''while''' loop will get executed for '''i''' equal to 0, 1, 2, 3 and 4.

|   03:32

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

|03:35

|Now, switch to the terminal.  

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| Type the following to check for any compilation or syntax error: 

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|'''perl hyphen c whileLoop dot pl'''

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| and press '''Enter.'''

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|The following line will be displayed on the terminal.

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|'''whileLoop.pl syntax OK '''

|03:56

|As there is no compilation or syntax error, we will execute the '''Perl''' script by typing: 

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|''' perl whileLoop dot pl'''

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|and press '''Enter'''.

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|The following output will be displayed on the terminal.  

| 04:14

| Now, let us look at '''do-while loop'''.

|   04:20

| The '''do..while''' statement will always execute the piece of code at-least once.

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| It will then check the condition and repeat the loop while the condition is true.

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|The syntax for '''do-while''' loop is as follows:

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| '''do''' space  

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|open curly bracket

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|piece of code to be executed while the condition is '''true'''  

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|close curly bracket then space

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|'''while''' space within the brackets '''condition''' and then semicolon.  

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|Open the Terminal and type:

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| '''gedit doWhileLoop dot pl space ampersand'''

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| and then press '''Enter'''.

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| This will open  '''doWhileLoop.pl''' file in '''gedit.'''  

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| Type the following piece of code: 

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|'''hash exclamation mark slash u s r slash bin slash perl'''  Press '''Enter'''.

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|'''dollar i equals to zero''' semicolon press '''Enter'''.

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|'''do''' space

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|open curly bracket '''Enter''' type:

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|'''print''' space double quote '''Value of i colon <space> dollar i backslash n'''  double quote complete semicolon

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|press '''Enter '''.

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|'''dollar i plus plus''' semicolon

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| press '''Enter '''.

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| close curly bracket.  

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|space '''while''' space open bracket '''dollar i less than or equal to four'''

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| close bracket semicolon.

| 06:10

| Here is the detail explanation of a '''do-while''' loop.  

| 06:13

| We have initialized the variable i to 0.  

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|First time, the '''do-while''' loop will print the output as  'Value of i colon 0' on the terminal without checking for condition.

|06:28

|'''$i++''' will increment the value of variable 'i' by one, each time loop gets executed.  

| 06:36

| Second time, the condition '$i' less than or equal to 4 will be checked.  

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| If the condition is '''True''', the loop will be executed again.  

|06:48

|In our case, second time the output displayed on terminal will be  'Value of i colon 1'.

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| The loop will get executed till the condition becomes '''False''' that is when variable 'i' becomes 5.  

| 07:05

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

|-

|Now, switch to terminal and type the following to check for any compilation or syntax error.

|'''perl hyphen c doWhileLoop dot pl'''

|  and press '''Enter.'''

| 07:23

|07:30

|As there is no compilation or syntax error, we will now execute the '''Perl''' script.  

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|Type: '''perl doWhileLoop dot pl'''

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|and press '''Enter'''.

| The following output will be displayed on the terminal.

| Now, let us see the actual difference between '''while''' and '''do-while''' loops.  

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| On the Terminal, type: 

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| '''gedit loop dot pl space ampersand'''

|-

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| This will open '''loop dot pl''' file in '''gedit. '''

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| Now type the piece of code shown.  

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|In the '''while''' loop condition, we are checking if the variable '''count''' is greater than zero.  

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|The condition is not true. So, the '''while''' loop code will not be executed even once.

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|In the '''do...while''' loop, we are first executing the code and then checking the condition.  

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|So, the code will be executed at least once.  

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|Then the condition whether the variable '''count''' is greater than zero, is checked.  

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|The condition is not '''True'''. So, the loop will exit.  

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|Now, press '''Ctrl+s''' to '''save''' the file.  

|09:05

|Now, switch to terminal and type the following to check for any compilation or syntax errors.  

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|'''perl hyphen c loop dot pl'''

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|and press '''Enter.'''

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|The following line will be displayed on the terminal.  

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|'''loop dot pl syntax OK'''

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|As there is no compilation or syntax error, let us execute the '''Perl''' script  

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|by typing '''perl loop dot pl'''

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|and press '''Enter.'''

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|The following output will be displayed on the terminal.  

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|09:46

|Here we can see, there is no output message displaying ''' 'I am in while loop' '''.

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|This message was what we printed inside the ''''while'''' loop.  

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|This implies that  

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|'''do-while''' loop executes at-least once before evaluating the condition

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|whereas '''while''' loop does not get executed even once when the condition specified is '''False'''.  

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|I hope the difference is clear to you now.  

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|That's all there is to '''while''' and '''do-while''' loops.  

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|Let us summarize.  

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|In this tutorial, we have learnt: 

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|'''while''' loop and '''do-while''' loop in '''Perl'''  

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|using sample programs.  

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|Here is an assignment for you -  

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|Print ''' 'Hello Perl' '''

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|till the count of variable reaches 10

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|by using '''while''' loop and '''do-while''' loops.

|10:41

|Watch the video available at the following link.

|10:45

|It summarizes the Spoken Tutorial project.

|10:49

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

| 10:53

|The Spoken Tutorial Project Team:

| 10:56

| Conducts workshops using spoken tutorials.

|11:00

| Gives certificates to those who pass an online test.

    

|11:04

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

|11:17

|11:24

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

| 11:36

| Hope you enjoyed this '''Perl''' tutorial.  

|11:40

|Thanks for joining.