Difference between revisions of "BASH/C2/Conditional-Loops/English-timed"

|'''Time'''

|'''Narration'''

| Dear friends, welcome to the '''spoken tutorial''' on '''loops''' in '''BASH'''.

|  In this tutorial, we will learn:

|'''for loop'''  

|'''while loop'''<br/> with a few examples.

| To record this tutorial, I am using:

|'''Ubuntu Linux''' 12.04 '''Operating System '''

|'''GNU BASH''' version 4.1.10

| Please note, '''GNU bash''' version 4 or above is recommended to practice this tutorial.

| 00:34  

|  Let us start with an introduction to ''' loops'''.

| 00:37  

| '''Loops''' are used to '''execute''' a group of '''statements''' repeatedly.

| 00:43

| 00:45

| 00:49

| 00:51

| and this is the end of '''for loop'''.

| 00:55

| 00:58

| 01:03

| 01:06

| and end of '''for loop'''.

| 01:09

| Let us see an example of '''for loop''' using the first syntax.

| 01:14

| 01:20  

|  Note that our filename is '''for.sh'''.

| 01:25  

| 01:28

|  The variable '''number''' will store the '''value''' given by user.  

|  01:34

|  01:37

| Now, we initialize the '''variable''' '''sum''' as zero.

|  01:42  

| 01:45  

| First, we initialize 'i' to 1.

| 01:48  

| Then we check whether 'i' is less than or equal to '''number'''.

| 01:54

|  Now here, we calculate the '''sum''' as '''sum plus i'''

|  02:00

| 02:03   

|  After this, we increment the '''value''' of 'i' by 1.

| 02:08

|  And then we check the '''condition''' till this '''condition''' is '''False'''.

|  02:14

|  02:19

|  Let us '''execute''' the program and observe what happens.

| 02:24   

|  On the '''terminal''', type - '''chmod +x for.sh'''

| 02:31   

|  02:36   

|  I will enter '''5''' as the '''input''' number.

|  02:40   

| The '''sum''' that is calculated for each value of 'i' is displayed.

|  02:46   

| After that, the last line of the '''output''' is displayed:

|  02:50

| '''"Sum of first n numbers is 15"'''.

|  02:54

| Now, let us see the flow of the program.

|  02:57

| Let me resize the '''windows'''.

|  03:00

|  First, we have value of 'i' as 1.

|  03:04  

|  Then we check whether '''1''' is less than or equal to ''' 5.'''

|  03:10

| Since the condition is '''True,''' we calculate the '''sum''' as '''0 + 1.'''

|  03:16

| Now we have the '''sum '''as '''1.'''

|  03:20

| 03:24  

|  Next, 'i' is incremented by '''1''' and the new value of 'i' is '''2.'''

| 03:31  

| Then we check whether ''' 2 ''' is less than or equal to ''' 5.'''

|  03:36  

| The '''condition''' is '''True''' and now '''sum''' will be ''' 1 + 2 ''' i.e ''' 3.'''

| 03:44

|    'i' is then incremented by '''1''' and then the new value of 'i' is '''3.'''

| 03:51

| 03:55  

|  The '''script''' will continue to add the next value of 'i' to the previous value in ''' sum.'''

| 04:02  

| This will continue till '''<nowiki>i<=5</nowiki>''' is '''False.'''

| 04:09  

| 04:14   

| 04:20   

| I have written the '''code''' in this file and named it as '''for-loop.sh'''.

| 04:27   

| 04:32  

| This is the '''shebang line.'''

| 04:35  

|  Then we have '''for''' loop.

| 04:37  

| ''' 'ls' ''' '''command''' lists the directory content.

| 04:41  

| 04:46  

| This will list all the files present in your '''home directory'''.

|  04:51  

| 04:53

|  Let us '''execute''' the '''script''' on the '''terminal''' by typing -  

| 04:58

| 05:04

| Type: '''./for-loop.sh'''

| 05:09

| 05:14   

|  Now we will learn about ''' while loop.'''

| 05:18   

| 05:21  

end of '''while loop'''.

| 05:27

| This means that the '''while''' loop will execute as long as the '''condition''' is '''True.'''

|05:34

|Let us see an example of '''while loop.'''

|  05:37

| Here, I have named it as '''while.sh'''.

|  05:42

|05:49

| Let us go through the '''code'''.

|05:52

|05:59

|  Next, we declare variables 'i' and '''sum''' and initialize them to 0 (zero).

|06:06

|Now, this is the '''while''' '''condition'''.

| 06:08

| Here, we check whether 'i' is '''less than or equal''' to value of '''number''' given by the user.

|  Then we calculate the '''sum''' by adding value of 'i' to value of '''sum'''.

|  Next, we increment the value of 'i' with '''2'''.

|  06:28  

|  06:33  

| And the '''while loop''' is repeated till the value of 'i' exceeds the value of '''number.'''

|  06:40  

| 06:47  

| Let us '''execute''' the program.

| 06:50  

| 06:52  

| '''"Sum of even numbers within the given range is 56".'''

| 07:11  

|  Let me resize the '''window''' and explain the '''output'''.

|  First we check whether 'i' which is 0, is less than or equal to the '''number''' which is '''15'''.

|  The '''condition''' is '''True.''' Hence '''sum''' will be '0+0' i.e 0.

| Now 'i' will be incremented by '''2''' and the new value of 'i' is ''' 2.'''

| 07:37

|  The condition again is '''True;''' so we add '''0+2.'''

|  Again the value of 'i' will be incremented by '''2'''.

| So, now value of 'i' will be '''2+2''' i.e '''4.'''

|  And the next value of ''' sum ''' will be '''4+2''' i.e '''6.'''

|  In the same way, the '''script''' will continue to add '''2''' to the previous value of 'i', till it exceeds '''15'''.

| Let us summarize. In this tutorial, we learned two different syntax of '''for loop ''' and we also learned about the '''while loop.'''

| As an assignment -find the sum of the first "n" prime numbers.

|  Watch the video available at the link shown below.

| It summarizes the Spoken-Tutorial project.

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

|  The Spoken Tutorial Project team:

|Conducts workshops using spoken tutorials.

|Gives certificates to those who pass an online test.

|09:11  

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

| 09:14  

| It is supported by the National Mission on Education through ICT, MHRD, Government of India.

| More information on this mission is available at the link shown below.

|  This is Ashwini Patil from IIT Bombay, signing off.