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

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