Ruby/C2/Control-Statements/English-timed
From Script | Spoken-Tutorial
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 , 'elsif' statement |
00:11 | 'else, 'case' statements. |
00:14 | Here we are using: 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. 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” , ruby code |
02:20 | else, 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.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 . 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 . when “value 2” ruby code |
06:31 | else ruby code . 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. In this tutorial, we have learnt to use: |
09:10 | if statement |
09:12 | else construct, if-elsif and |
09:15 | case statements. |
09:17 | As an assignment- 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. |