Difference between revisions of "Ruby/C2/Control-Statements/English-timed"
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Revision as of 10:18, 23 December 2015
| Time | Narration |
| 00:01 | Welcome to the spoken tutorial on Control Statements in Ruby. |
| 00:06 | In this tutorial, we will learn to use: |
| 00:08 | * 'if' statement |
| 00:09 | * 'elsif' statement |
| 00:11 | * 'else |
| 00:12 | * 'case' statements. |
| 00:14 | Here we are using: |
| 00:15 | * Ubuntu version 12.04 |
| 00:18 | * Ruby 1.9.3. |
| 00:21 | To follow this tutorial, you must have Internet connection. |
| 00:24 | You must also have knowledge of Linux commands, Terminal and Text-editor. |
| 00:30 | 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 control hyphen statements. |
| 00:47 | Now that we are in that folder, let’s move ahead. |
| 00:52 | The syntax of the 'if' statement in Ruby is as follows: |
| 00:56 | if “condition” |
| 00:58 | ruby code |
| 00:59 | end |
| 01:01 | Let us look at an example. |
| 01:03 | Create a new file in gedit as shown in the basic level Ruby tutorials. |
| 01:08 | Name it if hyphen statement dot rb. |
| 01:12 | I have a working example of the if statement. |
| 01:15 | You can pause the tutorial and type the code as we go through it. |
| 01:19 | I have declared an if statement in this example. |
| 01:23 | First, I declare a local variable my_num and assign the value 2345 to it. |
| 01:31 | Then I declare an if statement. |
| 01:34 | The puts method declared within the if statement will display the output. |
| 01:39 | The if statement will check if the value of my_num is greater than 0. |
| 01:43 | If it is, it will print out the specified string. |
| 01:47 | Now, let us switch to the terminal and type: |
| 01:51 | ruby space if hyphen statement dot rb. |
| 01:57 | The output will display “The value of my_num is greater than 0”. |
| 02:02 | This output proves that the if condition returned true. |
| 02:07 | You should now be able to write your own 'if' statement in Ruby. |
| 02:12 | Let's look at the 'if-else' statement next. |
| 02:16 | The syntax for using else is: |
| 02:18 | if “condition” |
| 02:19 | ruby code |
| 02:20 | else |
| 02:21 | ruby code |
| 02:22 | end |
| 02:24 | Let us look at an example. |
| 02:26 | Create a new file in gedit as shown in the basic level Ruby tutorials. |
| 02:30 | Name it if hyphen else hyphen statement dot rb. |
| 02:37 | I have a working example of the 'if-else' statement. |
| 02:40 | You can pause the tutorial and type the code as we go through it. |
| 02:44 | I have declared an if-else statement in this example. |
| 02:48 | First I declare a local variable my_num and assign the value of -1 to it. |
| 02:55 | Then I declare an if statement. |
| 02:58 | The 'if' statement will check if the value of 'my_num' is greater than 0. |
| 03:03 | If it is, it will print out the specified string. |
| 03:06 | If not, it will go to the else statement. |
| 03:10 | And it will print out the string that is specified there. |
| 03:13 | Now, let us switch to the terminal and type: |
| 03:18 | ruby space if hyphen else hyphen statement dot rb |
| 03:26 | and see the output. |
| 03:27 | The output will display “The value of my_num is lesser than 0”. |
| 03:32 | This shows that the else statement was executed. |
| 03:35 | You should now be able to write your own if-else statement in Ruby. |
| 03:41 | Let's look at the if-elsif statement next. |
| 03:45 | The syntax for using elsif is: |
| 03:48 | if “condition” ruby code |
| 03:50 | elsif “condition” ruby code |
| 03:52 | else ruby code |
| 03:54 | end |
| 03:55 | Let us look at an example. |
| 03:58 | Create a new file in gedit as shown in the basic level Ruby tutorials. |
| 04:01 | Name it if hyphen elsif hyphen statement dot rb. |
| 04:07 | I have a working example of the if-elsif statement. |
| 04:10 | You can pause the tutorial and type the code as we go through it. |
| 04:14 | I have declared an if-elsif statement in this example. |
| 04:19 | Here also, I have declared a local variable my_num and assigned the value -1 to it. |
| 04:25 | Then I declare an if statement. |
| 04:28 | The if statement will check if the value of my_num is greater than 0. |
| 04:32 | If it is, it will print out the specified string. |
| 04:35 | If this is not true, it will go into the elsif section. |
| 04:39 | It will now check if the value of my_num is equal to -1. |
| 04:43 | If it is true, it will print out the string that is specified there. |
| 04:46 | If the value of my_num is neither greater than 0 nor equal to -1, it will go into the else section. |
| 04:54 | But, since the value of my_num = -1 it will not proceed to the else block. |
| 05:00 | And, it will exit the conditional statement. |
| 05:03 | Now, let us switch to the terminal and type: |
| 05:07 | ruby space if hyphen elsif hyphen statement dot rb |
| 05:15 | and see the output. |
| 05:17 | The output will display “The value of my_num is -1 and is lesser than 0”. |
| 05:23 | Let's go back to our file and change the value of my_num to 5. |
| 05:29 | Let's save the code and execute it on the terminal. |
| 05:35 | So, now it fulfills the if condition and the specified string is printed. |
| 05:42 | "The value of my_num is greater than 0". |
| 05:45 | Let's go back to our file and change the value of my_num to -5. |
| 05:50 | Let's save the code and execute it on the terminal. |
| 05:55 | In this case, it fulfills the else condition and the puts statement within the else block gets executed. |
| 06:03 | You should now be able to write your own if-elsif statement in Ruby. |
| 06:08 | Let us look at the 'case' statement next. |
| 06:12 | The 'case' statement is a control flow statement based on a particular selection. |
| 06:17 | Let us look at the syntax of the 'case' statement in order to understand this statement. |
| 06:22 | The syntax for using case is: |
| 06:24 | case variable |
| 06:26 | when “value 1” |
| 06:28 | ruby code |
| 06:29 | when “value 2” |
| 06:30 | ruby code |
| 06:31 | else |
| 06:32 | ruby code |
| 06:34 | end |
| 06:35 | Let us look at an example. |
| 06:37 | Create a new file in gedit as shown in the basic level Ruby tutorials. |
| 06:41 | Name it case hyphen statement dot rb. |
| 06:44 | I have a working example of the 'case' statement. |
| 06:48 | You can pause the tutorial and type the code as we go through it. |
| 06:52 | I have declared a case statement in this example. |
| 06:55 | Here, I have a print statement which will print a question on the terminal. |
| 07:01 | Then I call a gets which will accept a single line of data from the standard input. |
| 07:09 | Then I strip the input data of any new line characters using chomp. |
| 07:15 | I assign the result to a variable named domain. |
| 07:18 | Then I declare a case statement. |
| 07:22 | Within that, I declare a when statement . |
| 07:25 | This checks whether the specified string matches the value of domain. |
| 07:30 | First, it checks whether the value of domain is “UP”. |
| 07:34 | If it is so, it will print out “Uttar Pradesh” and exit the case statement. |
| 07:39 | If domain is not “UP”, it checks whether the value of domain is “MP”. |
| 07:44 | If it is so, it will print out “Madhya Pradesh” and so on. |
| 07:48 | It will continue checking the value of domain if no match was found so far. |
| 07:53 | At this point, it will encounter the else statement |
| 07:56 | as none of the above conditions were true. |
| 07:59 | It will subsequently execute the ruby code that follows the else declaration. |
| 08:03 | It will print “Unknown” as per our example. |
| 08:07 | Now, save the file. Switch to the terminal and type: |
| 08:11 | ruby space case hyphen statement dot rb. |
| 08:18 | “Enter the state you live in:” will be displayed on the terminal. |
| 08:22 | Type in “UP” and see the output. |
| 08:25 | The output will display “Uttar Pradesh”. |
| 08:28 | Next, execute the Ruby file again, like before. |
| 08:31 | This time, at the prompt, type: “KL” and see the output. |
| 08:36 | It will print “Kerala”. |
| 08:38 | Next, execute the file one more time. |
| 08:41 | This time, at the prompt, type: in “TN” and see the output. |
| 08:47 | It will print “Unknown”. |
| 08:50 | This is because none of the cases were satisfied. So, the default else statement is executed. |
| 08:58 | You should now be able to write your own case-statements in Ruby. |
| 09:03 | This brings us to the end of this Spoken Tutorial. |
| 09:07 | Let's summarize. |
| 09:08 | In this tutorial, we have learnt to use: |
| 09:10 | * if statement |
| 09:12 | * else construct |
| 09:13 | * if-elsif and |
| 09:15 | * case statements. |
| 09:17 | As an assignment- |
| 09:18 | Write a Ruby program |
| 09:20 | that prompts a user to enter a number, |
| 09:23 | then use the appropriate control-statement |
| 09:26 | to check if the number is a multiple of 2. |
| 09:29 | If it is, then print: “The number entered is a multiple of 2”. |
| 09:35 | If not, it should check- if it is a multiple of 3. |
| 09:38 | If it is, then print: “The number entered is a multiple of 3”. |
| 09:43 | If not, it should check if it is a multiple of 4. |
| 09:47 | If it is, then print: “The number entered is a multiple of 4”. |
| 09:51 | If not, it should print: “The number is not a multiple of 2, 3 or 4”. |
| 09:56 | Watch the video available at the following link. |
| 10:00 | It summarizes the Spoken Tutorial project. |
| 10:03 | If you do not have good bandwidth, you can download and watch it. |
| 10:07 | The Spoken Tutorial project team: |
| 10:09 | * Conducts workshops using spoken tutorials. |
| 10:13 | * Gives certificates to those who pass an online test. |
| 10:16 | For more details, please write to:
contact@spoken-tutorial.org |
| 10:21 | Spoken Tutorial project is a part of the Talk to a Teacher project. |
| 10:26 | It is supported by the National Mission on Education through ICT, MHRD, Government of India. |
| 10:32 | More information on this mission is available at:
spoken hyphen tutorial dot org slash NMEICT hyphen Intro. |
| 10:41 | This is Anjani Nair, signing off. Thanks for watching. |
