View source for Ruby/C2/Logical-and-other-Operators/English-timed

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|| '''Time'''
|| '''Narration'''

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|  00:02
| Welcome to this '''Spoken Tutorial''' on '''Logical & Other Operators. '''

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| 00:06
| In this tutorial, we will learn: 

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| 00:09
|* '''Logical Operators '''

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| 00:11
|*'''Parallel assignment''' and 

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|* '''Range Operators '''.

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|  00:15
|Here, we are using: 

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|* '''Ubuntu Linux''' version '''12.04''' 

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|  00:20
|* ''' Ruby 1.9.3  '''

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| 00:23
|To follow this tutorial, you must know how to use ''' Terminal''' and '''Text editor''' in '''Linux'''. 

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| 00:29
|You must also be familiar with ''''irb''''. 
  
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| If not, for relevant tutorials, please visit our website. 

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| 00:38
|'''Logical operators''' are also known as ''' Boolean operators'''

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|  00:42
|  because they evaluate parts of an expression 

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| 00:45
|and return a ''' true''' or ''' false''' value. 

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| 00:48
|'''Logical Operators''' are- 

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| 00:51
|*  double ampersand (&&) that is '''and''' 

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| 00:54
|*  double '''pipe'''  that is '''or''' 

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|*  Exclamation mark (!) that is '''not'''. 

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|*  '&&' (double ampersand) and '''and''' evaluate to '''true''' only if both the expressions are '''true.''' 

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| 01:07
|Second expression is evaluated only if the first is '''true.''' 

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| 01:12
| Difference in the two forms is precedence.

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|Symbolic '''and'''  that is'''&&(double ampersand)''' has higher precedence. 

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| 01:20
|Let's see some examples now. 

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| 01:22
|We will use '''irb''' for this. 

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|  01:25
|  Open the ''' terminal''' by pressing '''Ctrl, Alt''' and '''T''' keys simultaneously. 

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|  01:31
|Type "irb" and press '''Enter''' to launch '''interactive Ruby'''.

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|  01:36
| Type: ''' 3 greater than 2 space double ampersand space 4 less than 5'''. 

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| Press ''' Enter'''.

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| We get the output as "true".

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|Here, expression1 that is 3>2 is '''true'''. 

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| 01:59
|Expression 2 that is 4<5 is also '''true.''' 

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|02:03
|Since both the expressions are '''true''', we get output as '''true.''' 

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| 02:08
|Now, press '''Up-Arrow''' key to get the previous command. 

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|02:12
| And replace the double ampersand symbol with the word "and". 

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|  Press '''Enter'''.

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|  02:19
|We get the same result.  

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|  02:22
| Now, press up-arrow key again to get the previous command. 

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|  02:27
| In  expression1, replace greater-than sign with less-than,

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|press ''' Enter '''

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|  02:35
| We get the output as "false".

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| 02:38
|This is because  3 < 2 is '''false.'''

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| Since the first expression is '''false''', the second expression will not be evaluated.  

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| 02:49
| So, we get the output as "false". 

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| 02:53
| '''double pipe''' and '''or''' evaluate to '''true''', if either '''expression''' is '''true.''' 

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| 02:59
|Second expression is evaluated only if first is '''false.''' 

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| 03:04
|Difference in the two forms is '''precedence.''' 

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| 03:07
|Symbolic '''or''' i.e '''double pipe''' has higher '''precedence.''' 

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|  03:11
|  Now, let's try some examples.  

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|Type: '''10 greater than 6 space double pipe space 12 less than 7'''

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| Press  '''Enter.''' 

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|We get output as "true".

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|Here expression 1, that is '''10>6''', is '''true'''.

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| 03:35
| Since the first expression is '''true''', second expression will not be evaluated. 

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| 03:40
|So, we get the output as '''true. '''

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|  03:42
|  Now, press the '''Up-Arrow''' key to get the previous command. 

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|  03:46
|  In '''expression 1''' replace '''greater than''' sign with '''less than''' sign

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|  and replace '''pipe''' symbol with the word '''or.''' 

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|  Press '''Enter.''' 

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|Here, '''expression1''' that is 10<6 is '''false. '''

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|  04:05
| '''Expression 2''' that is 12<7 is also '''false. '''

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|  04:10
|  Since both the expressions are '''false''', we get output as "false". 

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|'!' (exclamation mark ) and '''not''' operators return the opposite value of the expression. 

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|  If the expression is '''true''', exclamation mark operator will return a '''false''' value. 

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| 04:27
|It will return '''true''' if the expression is '''false'''. 

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|  04:30
| Difference in the two forms is '''precedence.'''

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| 04:33
| Symbolic '''not''', that is '!', has higher '''precedence.''' 

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|   04:37
| Let's try out the "not" operator. 

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| 04:40
|First, type: '''10 double equal to 10'''

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|  Press '''Enter '''.

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|We get the output as "true".

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|To '''invert''' the result of above expression, 

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|  04:53
| let's add the "not" operator before the expression. 

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|Type: exclamation mark within brackets '''10 double equal to 10 '''.

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| Press '''Enter. '''

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|We get the output as "false".

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| Press '''Ctrl+L''' simultaneously to clear the '''irb''' console. 

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| 05:15
|Next, let us learn about '''parallel assignment.'''

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|Multiple variables can be initialized with a single line of '''Ruby''' code, through '''parallel assignment. '''

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| Let's switch to the '''terminal.'''

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|Let's declare three variables 'a', 'b', 'c' using '''parallel assignment. '''

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| Type: '''a comma b comma c equal to 10 comma 20 comma 30'''

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| and press '''Enter. '''

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|Here, 10 will be assigned to variable 'a',

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|20 will be assigned to variable 'b'

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|30 will be assigned to variable 'c'.

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|The right-hand side acts as an '''array'''. 

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|If we list multiple variables on the left hand side then the array is unpacked and assigned into the respective variables. 

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|We will learn about '''arrays''' in detail, in the upcoming tutorials. 

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| For now, let's check whether the assignment is done properly. 

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| Type 'a' and press '''Enter.'''

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|Value 10, stored in variable 'a', is displayed. 

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|Type 'b' and press '''Enter.'''

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|We get 20. 

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| Type 'c' and press '''Enter.'''

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|30 is displayed. 

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|  '''Parallel assignment''' is also useful for swapping the values stored in two variables. 

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| 06:45
|Let us swap the values of variables 'a' and 'b'.

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|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''' 

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| Press '''Enter. '''

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| We get the output as '''a=10'''

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| 07:16
|'''b=20.'''

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|Now, let's swap 'a' and 'b'.

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| 07:23
|To do so, type: 

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|'''a comma b equal to b comma a '''

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|Press '''Enter.''' 

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| Press '''Up-Arrow''' key twice to get the '''puts''' command and press '''Enter.'''

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|  07:39
|  We get the output as- 

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|'''a=20 '''

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| 07:44
| '''b=10 '''.

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| 07:47
| We will now learn about '''range''' in '''Ruby.'''

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|The values in a '''range''' can be numbers, characters, '''string'''s or '''object'''s. 

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| 07:58
|'''Ranges''' are used to express a '''sequence. '''

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|'''Sequence range''' is used to create a range of successive values. 

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|It consists of a start value, range of values and an end value. 

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|'''(..) two dot operator''' creates ''' inclusive range. '''

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|'''(...) three dot operator''' creates an '''exclusive range. '''

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|'''Ranges''' are used to identify whether a value falls within a particular range too. 

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|We do this using (===) the '''equality''' operator.  

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| 08:30
|Let us try out some examples on '''ranges.'''

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| 08:33
|Let's switch to '''terminal. '''

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|Type: within brackets ''' 1 two dots 10''' then '''dot to underscore a''' 

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|'''Two dot''' operator creates '''inclusive range. '''

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|'''Inclusive operator''' includes both, begin and end values, in a range. 

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|Here '''to_a''' '''method''' is used to convert a '''range''' to a list. 

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|Press '''Enter. '''

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|Here, you can see the values 1 and 10 are included in the range. 

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|Now, we will see an '''exclusive range''' operator. 

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|Type:  within brackets '''1 three dots 10''' then '''dot to underscore a'''. 

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| 09:27
|'''Three dot''' operator creates an '''exclusive range. '''

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|'''Exclusive range''' operator excludes the end value from the sequence. 

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|Press '''Enter. '''

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| 09:39
|Here, the end value 10 is not included in the range. 

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| 09:45
|Now, let's check whether 5 lies in the range of 1 to 10. 

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| 09:50
|Type: within brackets '''1 two dots 10 three times equal to''' and then '''5'''. 

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| 10:00
|Press '''Enter. '''

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| 10:02
|Equality operator is used to check whether a value lies in the range. 

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| 10:07
|We get the output as "true" since 5 lies in the range 1 to 10. 

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| 10:14
|This brings us to the end of this Spoken Tutorial. 

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| 10:17
|In this tutorial, we have learnt: 

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| 10:20
|* '''Logical operator''' i.e double ampersand, double '''pipe''' and exclamation mark operators. 

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| 10:27
|* '''Parallel assignment''' Ex: a, b, c = 10, 20, 30 

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| 10:34
|* '''Range Operator- Inclusive operator '''(..) and '''Exclusive operator(...)'''.

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| 10:39
|As an assignment, 

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| 10:41
|declare two variables using '''parallel assignment''' and 

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| 10:45
|check whether their sum lies between 20 and 50. 

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|  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.

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| 11:34
|This script has been contributed by the spoken tutorial team, '''IIT Bombay'''. 

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| 11:38
|And this is Shalini Nair, signing off.  Thank you. 

|}