Difference between revisions of "Ruby/C3/while-and-until-Looping-Statements/English-timed"
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Revision as of 23:06, 6 January 2016
| Time | Narration |
| 00:01 | Welcome to the tutorial on while and until loops in Ruby. |
| 00:06 | In this tutorial, we will learn to use- |
| 00:09 | * 'while' loop |
| 00:10 | * 'until' loop |
| 00:11 | * redo and |
| 00:12 | * break. |
| 00:13 | We are using: |
| 00:14 | * Ubuntu version 12.04 |
| 00:17 | * Ruby 1.9.3 |
| 00:20 | To follow this tutorial, you must have Internet connection. |
| 00:25 | You must also have knowledge of Linux commands, Terminal and Text-editor. |
| 00:29 | If not, for relevant tutorials, please visit our website. |
| 00:34 | Before we begin, recall that we had created ttt directory earlier. |
| 00:38 | Let's go to that directory. |
| 00:41 | Then to ruby hyphen tutorial and looping hyphen statements directories. |
| 00:46 | Now that we are in that folder, let’s move ahead. |
| 00:50 | The syntax of the while loop in Ruby is as follows: |
| 00:54 | while “boolean expression” |
| 00:56 | ruby code |
| 00:57 | end |
| 00:58 | Let us look at an example. |
| 01:01 | Create a new file in gedit as shown in the basic level Ruby tutorials. |
| 01:05 | Name it while hyphen loop dot rb. |
| 01:09 | I have a working example of the 'while' loop. |
| 01:13 | Now, let us switch to the terminal and type: gedit space while hyphen loop dot rb space & (ampersand) |
| 01:24 | You can pause the tutorial, type the code as we go through it. |
| 01:28 | I have declared a while loop in this example. |
| 01:32 | First, I declared a local variable 'i' and initialized it with value 0. |
| 01:38 | Then I declare a 'while' loop. |
| 01:41 | This loop will execute as long as the variable 'i' is greater than -10. |
| 01:46 | The puts method, declared within the while loop, will display the output. |
| 01:51 | After the output is displayed, we decrement the value of 'i' by 1. |
| 01:56 | 'i' will adopt this decremented value before the next iteration. |
| 02:01 | The variable 'i' gets decremented in every iteration. |
| 02:04 | This goes on till 'i' reaches the value -10. |
| 02:09 | At this point, the 'while' condition fails. |
| 02:12 | It subsequently breaks out of the loop and stops printing the output. |
| 02:16 | Now, let us switch to the terminal and type: ruby space while hyphen loop dot rb and see the output. |
| 02:30 | The output will consist of a list of numbers 0 through -9. |
| 02:35 | You should now be able to write your own while loop in Ruby. |
| 02:40 | Let's look at the until loop next. |
| 02:43 | The syntax for the until loop in Ruby is - |
| 02:45 | until “boolean expression” |
| 02:47 | ruby code |
| 02:48 | end |
| 02:50 | Let us look at an example. |
| 02:52 | Now,let us switch to the terminal and type: gedit space until hyphen loop dot rb space & (ampersand) |
| 03:03 | You can pause the tutorial and type the code as we go through it. |
| 03:07 | I have declared an until loop in this example. |
| 03:12 | We had declared a local variable 'i' and initialized it to 0. |
| 03:16 | Then we declare an until loop. |
| 03:18 | This loop will execute as long as the variable 'i' is greater than -10. |
| 03:23 | The 'puts' method will display the output. |
| 03:27 | After the output is displayed, value of 'i' is decremented by 1. |
| 03:32 | 'i' will adopt this decremented value before the next iteration. |
| 03:36 | The variable 'i' gets decremented during every iteration. |
| 03:40 | This goes on till 'i' reaches the value -11. |
| 03:43 | At this point, the 'until' condition fails. |
| 03:46 | Subsequently, it breaks out of the loop and stops printing the output. |
| 03:51 | Now, switch to the terminal and type: ruby space until hyphen loop dot rb and see the output. |
| 04:03 | The output will consist of a list of numbers 0 through -10. |
| 04:08 | You should now be able to write your own until loop in Ruby. |
| 04:13 | Let's now move on to the redo construct. |
| 04:16 | The syntax for redo in Ruby is as follows: |
| 04:20 | a collection of objects. each do item |
| 04:25 | a conditional statement |
| 04:27 | ruby code |
| 04:28 | redo |
| 04:29 | end conditional |
| 04:30 | end loop |
| 04:32 | I have a working example of the redo loop. |
| 04:35 | Now, let us switch to the terminal and type: gedit space redo hyphen loop dot rb space &(ampersand ) |
| 04:48 | You can pause the tutorial and type the code as we go through it. |
| 04:52 | I have declared an each loop in this example. |
| 04:55 | We have declared an each loop to iterate through numbers 10 to 20. |
| 05:00 | Then, we define an if conditional statement. |
| 05:04 | The loop will execute for every number between 10 to 20. |
| 05:08 | It will enter the inner conditional if conditional block only if the value of 'i' is equal to 20. |
| 05:15 | The 'puts' method, declared within the each loop, displays the output. |
| 05:20 | Once the program enters the 'if' conditional block, it will first print the output. |
| 05:24 | Then it will execute redo. |
| 05:28 | redo will execute the iteration of the most internal loop. |
| 05:31 | It will do so, without checking the loop condition. |
| 05:34 | Our condition being if i == 20, |
| 05:38 | the result will be an infinite loop, since the value of 'i' will not change from 20. |
| 05:43 | Let's switch to the terminal and type:
ruby space redo hyphen loop dot rb |
| 05:52 | and see the output. |
| 05:53 | The output will consist of an infinite loop that never ends. |
| 05:58 | Press Ctrl + C to terminate the infinite loop. |
| 06:03 | Now, let us look at the break statement. |
| 06:06 | The syntax for the break statement in Ruby is - |
| 06:10 | a looping statement |
| 06:12 | a conditional statement |
| 06:13 | break |
| 06:14 | end conditional |
| 06:16 | ruby code |
| 06:17 | end loop |
| 06:18 | Let us look at an example. |
| 06:21 | Now, let us switch to the terminal and type:
gedit space break hyphen loop dot rb space ampersand. |
| 06:33 | You can pause the tutorial and type the code as we go through this example. |
| 06:38 | I have declared an each loop in this example. |
| 06:41 | It is similar to the one we used earlier. |
| 06:43 | The 'puts' method here, will display the output for numbers 11 to 19. |
| 06:49 | Once the value becomes 20, the program enters the conditional 'if' block. |
| 06:54 | At this point, it will encounter the break statement and breaks out of the loop. |
| 06:59 | Now, open the terminal and type: |
| 07:02 | ruby space break hyphen loop dot rb |
| 07:05 | and see the output. |
| 07:08 | The output will consist of numbers 10 through 19. |
| 07:13 | Now, you should be able to create your own break construct. |
| 07:17 | This brings us to the end of this Spoken Tutorial. |
| 07:20 | Let's summarize. |
| 07:22 | In this tutorial, we have learnt to use: |
| 07:24 | * while loop |
| 07:25 | * until construct |
| 07:26 | * redo |
| 07:27 | * break construct. |
| 07:29 | As an assignment- |
| 07:31 | Consider a range of numbers 100 to 115(inclusive), represented as Fahrenheit. |
| 07:38 | Write a Ruby program using |
| 07:40 | the appropriate loop construct |
| 07:42 | that uses the Fahrenheit to Celsius conversion formula |
| 07:46 | against the given range of numbers. |
| 07:49 | To display the output: “The temperature has reached a certain degree Celsius and has become unbearable” |
| 07:55 | when the temperature in Celsius is above 32 degree Celsius. |
| 08:00 | Watch the video available at the following link. |
| 08:03 | It summarizes the Spoken Tutorial project. |
| 08:07 | If you do not have good bandwidth, you can download and watch it. |
| 08:10 | The Spoken Tutorial project team: |
| 08:13 | * Conducts workshops using spoken tutorials. |
| 08:15 | * Gives certificates to those who pass an online test. |
| 08:19 | For more details, please write to contact@spoken-tutorial.org |
| 08:25 | Spoken Tutorial project is a part of the Talk to a Teacher project. |
| 08:29 | It is supported by the National Mission on Education through ICT, MHRD, Government of India. |
| 08:35 | More information on this mission is available at spoken hyphen tutorial dot org slash NMEICT hyphen Intro. |
| 08:44 | This is Anjana Nair, signing off. Thank you. |
