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 (!) 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 us 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 expression 1 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 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	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 summarises the Spoken Tutorial project.
10:56	If you do not have good bandwidth, you can download and watch it.
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11:19	It is supported by the National Mission on Education through ICT, MHRD, Government of India.
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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