Ruby: Symbol Review

Question 1

\

Answer 1

Escape sequence for string: Escapes the “" character.

Question 2

'

Answer 2

Escape sequence for single-quoted string. Escape the single quote character.

Question 3

"

Answer 3

Escape sequence for double-quoted string. Escape the double quote character.

Question 4

\n

Answer 4

Escape sequence for double-quoted string. Starts a new line.

Question 5

\s

Answer 5

Escape sequence for double-quoted string. Adds a space.

Question 6

\t

Answer 6

Escape sequence for double-quoted string. Adds a tabbed space (~5 spaces)

Question 7

\b

Answer 7

Escape sequence for double-quoted string. Deletes a space (backspace function). In IRB, only works with puts.

Question 8

\a

Answer 8

Escape sequence. Sends an alert to the user. The alert may be dependent on the user’s computer - it may flash, be an audio alert, etc.

Question 9

\f

Answer 9

Escape sequence. Begins a new line at the same point as the previous line ended.

example: puts “Hello\fWorld”

Hello
World
=> nil

Question 10

\v

Answer 10

Escape sequence. Begins a new line at the same point as the previous line ended.

example: puts “Hello\fWorld”

Hello
World
=> nil

Question 11

..

Answer 11

The two dot construction for a Ruby Range means INCLUSIVE of the final character.

Example:
(1..10)
=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Question 12

…

Answer 12

The three dot construction for a Ruby Range means EXCLUSIVE of the final character.

Example:
(1…10)
=> [1, 2, 3, 4, 5, 6, 7, 8, 9]

Question 13

||

Answer 13

Called Logical OR Operator. If any of the two operands are non zero then then condition becomes true. Same as ‘or’ operator.

Example:

(a || b) is true.

Question 14

&&

Answer 14

Called Logical AND operator. If both the operands are non zero then then condition becomes true. Same as ‘and’ operator.

Example:

(a && b) is true.

Question 15

not

Answer 15

Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true then Logical NOT operator will make false.

Example:

not(a && b) is false.

Question 16

!

Answer 16

Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true then Logical NOT operator will make false.

Example:

!(a && b) is false.

Question 17

or

Answer 17

Called Logical OR Operator. If any of the two operands are non zero then then condition becomes true. Same as ‘||’ operator.

Example:

(a or b) is true.

Question 18

and

Answer 18

Called Logical AND operator. If both the operands are true then then condition becomes true. Same as ‘&&’ operator.

Example:

(a and b) is true.

Question 19

+

Answer 19

Addition - Adds values on either side of the operator.

Example:

a + b will give 30

Question 20

-

Answer 20

Subtraction - Subtracts right hand operand from left hand operand.

Example:

a - b will give -10

Question 21

*

Answer 21

Multiplication - Multiplies values on either side of the operator.

Example:

a * b will give 200

Question 22

/

Answer 22

Division - Divides left hand operand by right hand operand.

Example:

10 / 5 will give 2

Question 23

%

Answer 23

Modulus - Divides left hand operand by right hand operand and returns remainder.

Example:

10 % 4 will give 2

Question 24

**

Answer 24

Exponent - Performs exponential (power) calculation on operators.

Example:

6**3 will give 6 to the power 3

Question 25

==

Answer 25

Checks if the value of two operands are equal or not, if yes then condition becomes true.

Example:

(a == b) is not true.

Question 26

!=

Answer 26

Checks if the value of two operands are equal or not, if values are not equal then condition becomes true.

Example:

(a != b) is true.

Question 27

>

Answer 27

Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true.

Example:

(8 > 10) is not true.

Question 28

<

Answer 28

Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true.

Example:

(8 < 10) is true.

Question 29

> =

Answer 29

Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true.

Example:

(8 >= 10) is not true.

Question 30

<=

Answer 30

Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true.

Example:

(8 <= 10) is true.

Answer 31

Combined comparison operator. Returns 0 if first operand equals second, 1 if first operand is greater than the second and -1 if first operand is less than the second.

The spaceship operator is used to make comparisons. The results are given relative to zero.
Asking, which side do I belong to? LEFT OR RIGHT?

Example:

1 2 will give -1

Because 1 is LESS than 2, it is -1.

2 1 will give 1

Because 2 is GREATER than 1, it is 1.

Question 32

===

Answer 32

Used to test equality within a when clause of a case statement.

Example:

(1…10) === 5 returns true.

[Does any number in the range == 5?] true

Question 33

.eql?

Answer 33

True if the receiver and argument have both the same type and equal values.

Example:

1 == 1.0 returns true, but 1.eql?(1.0) is false.

Question 34

equal?

Answer 34

True if the receiver and argument have the same object id.

Example:

a = 2
a.equal?(2)

true

Question 35

=

Answer 35

Simple assignment operator, Assigns values from right side operands to left side operand.

Example:

c = a + b will assign value of a + b into c

Question 36

+=

Answer 36

Add AND assignment operator, It adds right operand to the left operand and assign the result to left operand.

Example:

c += a is equivalent to c = c + a

Question 37

-=

Answer 37

Subtract AND assignment operator, It subtracts right operand from the left operand and assign the result to left operand.

Example:

c -= a is equivalent to c = c - a

Question 38

*=

Answer 38

Multiply AND assignment operator, It multiplies right operand with the left operand and assign the result to left operand.

Example:

c *= a is equivalent to c = c * a

Question 39

/=

Answer 39

Divide AND assignment operator, It divides left operand with the right operand and assign the result to left operand.

Example:

c /= a is equivalent to c = c / a

Question 40

%=

Answer 40

Modulus AND assignment operator, It takes modulus using two operands and assign the result to left operand.

Example:

c %= a is equivalent to c = c % a

Further Explanation:

a = 10
a % 4
=> 2

if you all the variable “a” again, it will be still be 10, because it wasn’t assigned.

However, if you use:
a %= 4
=> 2

Then a has been set to 2.

Question 41

**=

Answer 41

Exponent AND assignment operator, Performs exponential (power) calculation on operators and assign value to the left operand.

Example:

c **= a is equivalent to c = c ** a

Question 42

defined?

Answer 42

defined? is a special operator that takes the form of a method call to determine whether or not the passed expression is defined. It returns a description string of the expression, or nil if the expression isn’t defined.

Example:

foo = 42
defined? foo # => “local-variable”
defined? $_ # => “global-variable”
defined? bar # => nil (undefined)
defined? method_call # True if a method is defined
defined? puts # => “method”
defined? puts(bar) # => nil (bar is not defined here)
defined? unpack # => nil (not defined here)

Question 43

? :

Answer 43

Ternary Operator; conditional.

If Condition is true ? Then value X : Otherwise value Y

if a == b ? “a”:”b”

Question 44

alias

Answer 44

Alias renames and duplicates (gives an alias to), but not replaces, a method name.

Example:

class User

def full_name
puts “Johnnie Walker”
end

alias name full_name
end

User.new.name #=>Johnnie Walker

Question 45

[ ]

Answer 45

Symbol for an array.

Question 46

::

Answer 46

The :: symbol is used to access variables that belong to a module.

For example:

module ExampleModule
tangerine = "orange-like fruit"

then on another sheet we require that.

require ‘.examplemodule’

ExampleModule::tangerine
^ to call variable

Question 47

Add-on modifiers (with if statements)

Answer 47

Ruby Statement modifiers let you tack conditional statements onto the end of a normal statement:

Examples:

mon, day, year = $1, $2, $3 if date =~ /(\d\d)-(\d\d)-(\d\d)/

puts “a = #{a}” if $DEBUG
print total unless total.zero?

Question 48

Toggle-style (adding modifiers after the ‘end’)

Answer 48

Example:

if artist == “John Coltrane” artist = “‘Trane”
end unless use_nicknames == “no”

Question 49

Case Expressions

Answer 49

2 types of case: the first, similar to a series of if statements, the second, you specify a target at the top of the case:

Example 1:

case
when song.name == "Misty"
puts "Not again!" when song.duration > 120
puts "Too long!" when Time.now.hour > 21
puts "It's too late" else
      song.play
    end

Example 2:

case command
    when "debug"
      dump_debug_info
      dump_symbols
    when /p\s+(\w+)/
dump_variable($1) when "quit", "exit"
exit else
print "Illegal command: #{command}" end

Question 50

Case Statements Using Then syntax

Answer 50

kind = case year
when 1850..1889 then "Blues"
when 1890..1909 then "Ragtime"
when 1910..1929 then "New Orleans Jazz"
when 1930..1939 then  "Swing"
when 1940..1950 then "Bebop"
else "Jazz"
end