Ruby/C2/Logical-and-other-Operators/English-timed

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Time Narration
00:02 Welcome to this Spoken Tutorial on Logical & Other Operators.
00:06 In this tutorial, we will learn:
00:09 Logical Operators
00:11 Parallel assignment and
00:13 Range Operators .
00:15 Here, we are using:
00:17 Ubuntu Linux version 12.04
00:20 Ruby 1.9.3
00:23 To follow this tutorial, you must know how to use Terminal and Text editor in Linux.
00:29 You must also be familiar with 'irb'.
00:33 If not, for relevant tutorials, please visit our website.
00:38 Logical operators are also known as Boolean operators
00:42 because they evaluate parts of an expression
00:45 and return a true or false value.
00:48 Logical Operators are-
00:51 double ampersand (&&) that is and
00:54 double pipe that is or
00:56 Exclamation mark (!) that is not.
01:00 '&&' (double ampersand) and and evaluate to true only if both the expressions are true.
01:07 Second expression is evaluated only if the first is true.
01:12 Difference in the two forms is precedence.
01:15 Symbolic and that is&&(double ampersand) has higher precedence.
01:20 Let's see some examples now.
01:22 We will use irb for this.
01:25 Open the terminal by pressing Ctrl, Alt and T keys simultaneously.
01:31 Type "irb" and press Enter to launch interactive Ruby.
01:36 Type: 3 greater than 2 space double ampersand space 4 less than 5.
01:47 Press Enter.
01:49 We get the output as "true".
01:53 Here, expression1 that is 3>2 is true.
01:59 Expression 2 that is 4<5 is also true.
02:03 Since both the expressions are true, we get output as true.
02:08 Now, press Up-Arrow key to get the previous command.
02:12 And replace the double ampersand symbol with the word "and".
02:17 Press Enter.
02:19 We get the same result.
02:22 Now, press up-arrow key again to get the previous command.
02:27 In expression1, replace greater-than sign with less-than,
02:32 press Enter
02:35 We get the output as "false".
02:38 This is because 3 < 2 is false.
02:43 Since the first expression is false, the second expression will not be evaluated.
02:49 So, we get the output as "false".
02:53 double pipe and or evaluate to true, if either expression is true.
02:59 Second expression is evaluated only if first is false.
03:04 Difference in the two forms is precedence.
03:07 Symbolic or i.e double pipe has higher precedence.
03:11 Now, let's try some examples.
03:15 Type: 10 greater than 6 space double pipe space 12 less than 7
03:23 Press Enter.
03:26 We get output as "true".
03:29 Here expression 1, that is 10>6, is true.
03:35 Since the first expression is true, second expression will not be evaluated.
03:40 So, we get the output as true.
03:42 Now, press the Up-Arrow key to get the previous command.
03:46 In expression 1 replace greater than sign with less than sign
03:52 and replace pipe symbol with the word or.
03:57 Press Enter.
04:00 Here, expression1 that is 10<6 is false.
04:05 Expression 2 that is 12<7 is also false.
04:10 Since both the expressions are false, we get output as "false".
04:15 '!' (exclamation mark ) and not operators return the opposite value of the expression.
04:20 If the expression is true, exclamation mark operator will return a false value.
04:27 It will return true if the expression is false.
04:30 Difference in the two forms is precedence.
04:33 Symbolic not, that is '!', has higher precedence.
04:37 Let's try out the "not" operator.
04:40 First, type: 10 double equal to 10
04:45 Press Enter .
04:47 We get the output as "true".
04:50 To invert the result of above expression,
04:53 let's add the "not" operator before the expression.
04:57 Type: exclamation mark within brackets 10 double equal to 10 .
05:04 Press Enter.
05:06 We get the output as "false".
05:10 Press Ctrl+L simultaneously to clear the irb console.
05:15 Next, let us learn about parallel assignment.
05:20 Multiple variables can be initialized with a single line of Ruby code, through parallel assignment.
05:26 Let's switch to the terminal.
05:29 Let's declare three variables 'a', 'b', 'c' using parallel assignment.
05:36 Type: a comma b comma c equal to 10 comma 20 comma 30
05:45 and press Enter.
05:47 Here, 10 will be assigned to variable 'a',
05:52 20 will be assigned to variable 'b'
05:54 30 will be assigned to variable 'c'.
05:56 The right-hand side acts as an array.
06:01 If we list multiple variables on the left hand side then the array is unpacked and assigned into the respective variables.
06:10 We will learn about arrays in detail, in the upcoming tutorials.
06:14 For now, let's check whether the assignment is done properly.
06:20 Type 'a' and press Enter.
06:23 Value 10, stored in variable 'a', is displayed.
06:28 Type 'b' and press Enter.
06:31 We get 20.
06:33 Type 'c' and press Enter.
06:37 30 is displayed.
06:40 Parallel assignment is also useful for swapping the values stored in two variables.
06:45 Let us swap the values of variables 'a' and 'b'.
06:50 Type: puts space within double quotes a equal to hash within curly brackets a comma within double quotes b equal to hash within curly brackets b
07:11 Press Enter.
07:13 We get the output as a=10
07:16 b=20.
07:20 Now, let's swap 'a' and 'b'.
07:23 To do so, type:
07:25 a comma b equal to b comma a
07:31 Press Enter.
07:33 Press Up-Arrow key twice to get the puts command and press Enter.
07:39 We get the output as-
07:41 a=20
07:44 b=10 .
07:47 We will now learn about range in Ruby.
07:50 The values in a range can be numbers, characters, strings or objects.
07:58 Ranges are used to express a sequence.
08:02 Sequence range is used to create a range of successive values.
08:06 It consists of a start value, range of values and an end value.
08:13 (..) two dot operator creates inclusive range.
08:16 (...) three dot operator creates an exclusive range.
08:20 Ranges are used to identify whether a value falls within a particular range too.
08:26 We do this using (===) the equality operator.
08:30 Let us try out some examples on ranges.
08:33 Let's switch to terminal.
08:36 Type: within brackets 1 two dots 10 then dot to underscore a
08:46 Two dot operator creates inclusive range.
08:50 Inclusive operator includes both, begin and end values, in a range.
08:57 Here to_a method is used to convert a range to a list.
09:03 Press Enter.
09:05 Here, you can see the values 1 and 10 are included in the range.
09:11 Now, we will see an exclusive range operator.
09:16 Type: within brackets 1 three dots 10 then dot to underscore a.
09:27 Three dot operator creates an exclusive range.
09:31 Exclusive range operator excludes the end value from the sequence.
09:37 Press Enter.
09:39 Here, the end value 10 is not included in the range.
09:45 Now, let's check whether 5 lies in the range of 1 to 10.
09:50 Type: within brackets 1 two dots 10 three times equal to and then 5.
10:00 Press Enter.
10:02 Equality operator is used to check whether a value lies in the range.
10:07 We get the output as "true" since 5 lies in the range 1 to 10.
10:14 This brings us to the end of this Spoken Tutorial.
10:17 In this tutorial, we have learnt:
10:20 Logical operator i.e double ampersand, double pipe and exclamation mark operators.
10:27 Parallel assignment Ex: a, b, c = 10, 20, 30
10:34 Range Operator- Inclusive operator (..) and Exclusive operator(...).
10:39 As an assignment,
10:41 declare two variables using parallel assignment and
10:45 check whether their sum lies between 20 and 50.
10:49 Watch the video available at the following link.
10:52 It summarizes the Spoken Tutorial project.
10:56 If you do not have good bandwidth, you can download and watch it.
11:00 The Spoken Tutorial project team:
11:03 Conducts workshops using spoken tutorials.
11:05 Gives certificates to those who pass an online test.
11:09 For more details, please write to:contact@spoken-tutorial.org
11:15 Spoken Tutorial project is a part of the Talk to a Teacher project.
11:19 It is supported by the National Mission on Education through ICT, MHRD, Government of India.
11:25 More information on this mission is available at: spoken hyphen tutorial dot org slash NMEICT hyphen Intro.
11:34 This script has been contributed by the spoken tutorial team, IIT Bombay.
11:38 And this is Shalini Nair, signing off. Thank you.

Contributors and Content Editors

PoojaMoolya, Pratik kamble, Ranjana, Sandhya.np14