Vanilla

Question 1

what native class method can you call to convert the object to a float?

Answer 1

.to_f

Question 2

what type of quotes can be used for string interpolation ?

Answer 2

only double quotes, normally double or single can be used to create a string

Question 3

describe and name all the methods to add and remove elements to the beginning and end of an Array

Answer 3

push/pop will add/remove from the end of an Array

shift/unshift will remove/add from the beginning of an Array

Question 4

what Array method can we use to remove duplicates?

Answer 4

Array.uniq

Question 5

what native class method can you call to convert the object to a string?

Answer 5

to_s

e.g. [1] pry(main)> 40.to_s => “40” [2] pry(main)> 40 => 40

Question 6

how do we create or use a range in Ruby?

Answer 6

(1..5) or (1…5) create a range that can be iterated over in a for loop with the items 1 to 5 inclusive and 1 to 4 inclusive respectively

we can also create an array out of them by doing (1..5).to_a

Question 7

can you access a variable created in a while loop from outside that loop?

Answer 7

no, it must be declared before going into the while loop if you want to do so. otherwise it is confined to the scope of that while loop

Question 8

how create blocks of comments?

Answer 8

=begin

kjsanfafdjsankfnkdjkjndfsa

=end

Question 9

how can we create a method that mutates a variable? (modifies in place)

Answer 9

with the .replace method. this will only work on string and arrays though, integers for example are too primative to be worked with in this way as they don’t store state (note the bang! isn’t required, but probably good practice

e.g.

def lev_pop!(array)
new_array = []
removed = array[-1]
array.each_with_index {
|element, i|
if i != array.length - 1
new_array.push(element)
end
}
array.replace(new_array)
return removed
end

array = (“a”..”f”).to_a
popped_elements = lev_pop!(array)
popped_array = array
p popped_elements
p popped_array

terminal:
“f”
[“a”, “b”, “c”, “d”, “e”]

Question 10

how to remove letters from a String?

Answer 10

String.slice, the argument is the index for the letter (if it was an array), can use ranges and negatives as well. it will return what was removed. slice! will also modify the String in place, leaving the “left over” letters

[248] pry(main)> test = “string”
=> “string”
[249] pry(main)> test.slice(0)
=> “s”
[250] pry(main)> test.slice(1)
=> “t”
[251] pry(main)> test.slice(1..3)
=> “tri”
[252] pry(main)> test.slice(-1)
=> “g”
[253] pry(main)> test.slice(-2..-1)
=> “ng”

Question 11

what is a class constructor and how do we use it?

Answer 11

a class contructor is used to instantiate a class into and object.

when we (or Ruby) define the class, there is a constructor method that must be called initialize, initialize is a reserved word. in here we define attributes and any arguments required to instantiate.

in order to create an object of class Foobar, we write:
some\_object = Foobar.new()

Question 12

how does the <=> aka spaceship operator work?

also generally what can it be useful for?

Answer 12

a <=> b :=
if a < b then return -1

if a = b then return 0

if a > b then return 1

if a and b are not comparable then return nil

it is useful for sorting an array

Question 13

how do we print to terminal in ruby code

Answer 13

puts e.g. puts 1+1

Question 14

what are the rules of thumb for where to put exception handling?

Answer 14

rule of thumb for where to put exception handling:

• anywhere that requires user input where they can input something that your code cannot accept or support or do anything with
• anything that uses some sort of database where a value or the class of the value could potentially be something unsupported or left blank etc
• anything using APIs to return results and anything using those results
• anything attempting internet/network communication

Question 15

native type method to remove trailing and leading white space?

native type method to remove only trailing white space?

Answer 15

String.strip

and

String.chomp

Question 16

describe the gotchya when using ARGV and there is a gets in your script

Answer 16

gets must be changed to STDN.gets

Question 17

what is another name for instance variable?

Answer 17

attribute

Question 18

how do we make an instance variable and how does it work?

Answer 18

putting an @ infront of the variable and it is accessable instance wide (each of object of that calss has it’s own independent @variable

Question 19

how access an index of an array where you know the contents but not the index value?

Answer 19

four_letter_animals[four_letter_animals.index(“elephant”)]

Question 20

what is an easy way in ruby to create a break point ?

Answer 20

add the line binding.pry (must require ‘pry’) first

you can check what values a variable is at this break point by simply typing in it’s name

e.g.

require ‘pry’

x = 0
until x == 5
p x
x += 1
binding.pry
y = 0
end

Question 21

how does Array.pop work?

Answer 21

pop with remove the last (or more with an integer argument) element of an array in place.

it will also return all the popped elements in an array

Question 22

describe how we can use instance variables

Answer 22

an instance variable has class scope

it cannot be used as a paremeter for a method in the class, but it can be passed as an argument to the method

Question 23

can you string together ruby methods?

Answer 23

yes

e.g.

some_string.reverse.downcase

Question 24

what Array method can we use to concatonate an array of strings and create a single string?

Answer 24

.join

e.g.

array_of_strings.join

Question 25

what is the inverse of #reject?

Answer 25

#select

Question 26

what does the gets method stand for and do

Answer 26

GET String, waits for user input

Question 27

what is another name for attribute?

Answer 27

instance variable

Question 28

what is ARGV

Answer 28

it is an argument that can be given at runtime via the command line running the script.

it can be accessed with ARGV[0], ARGV[1], etc

e.g.

ruby some_script -t

where in some_script, there is a conditional somewhere that executes if ARGV[0] == “-t”

Question 29

in what scenario would we definetly want to use Array.each to iterate rather than for item in array?

Answer 29

when we want to also receive the iterations index

Question 30

in ruby what is truthy and what is falsey?

Answer 30

literallyt everything that is no false or nil is truthy, even the integer 0 is truthy

Question 31

what is a String class method that can replace all occurances of one string with another?

Answer 31

.gsub (as in Global Substitute)

e. g.
poem. gsub(“toast”, “honey”)

Question 32

what native class method can you call to convert the object to a array?

Question 33

what native class method can you call to convert the object to a integer?

Answer 33

to_i

Question 34

how do we run a command in the terminal using ruby

Answer 34

em { background-color: lightgray; padding: 10px; border-radius: 10px; }

put the command in a backtick e.g.

touch example.txt

or

touch #{var_name}.txt

Question 35

before doing anything with an any enumerable, what should be the first step?

Answer 35

go to the documentation for enumerable and then the type of enumerable, e.g. array, range, hash, etc and see if it can be done via one of those methods first.

Question 36

how do we allow an instance method to be chainable?

Answer 36

by using

return self

Question 37

what is the result of “some string”.to_i ?

Answer 37

0

Question 38

how can we pass in and use an operator in a method?

Answer 38

we can use symbols and the .send method

e.g.

def arithmetic(num0, num1, operator)

result = num0.to_f.send(operator, num1.to_f)

return result

end

p arithmetic(1, 2, :+)

p arithmetic(4, 2, “-“)

p arithmetic(6, 4, :*)

p arithmetic(7, 3, “/”)

Question 39

how do you do less than and greater then in a case statement?

Answer 39

you can’t, you have to use a range

e.g.

case distance
when (0…10)
puts “long way to go but you’re doing amazing!”
when (10…20)
puts “almost halfway now, killing it!”
when (20…30)
puts “now for the final push, keep going!”
when (30…40)
puts “sprint!!!!”
end

Question 40

ruby naming convention?

Answer 40

name_variables_with_snake_case

ClassesUseCapitalCamelCase

Question 41

what does the .each method return?

Answer 41

it returns the original array, it does not return a modified array or anything at all in the block statement

Question 42

how to print a block of text in ruby?

Answer 42

print “””
somet text
some more
blah blah bhlah
“””

Question 43

map_with_index doesn’t exist as a core method, so what is the easy work around?

Answer 43

map.with_index

Question 44

hash keys can be defined in what way to save memory?

Answer 44

using symbols, like so

some_hash = {

symb: value
}

reference_a_hash = some_hash[:symb]

as opposed to

some_hash = {

“string_key” => value

23 => value
}

reference_a_hash = some_hash[“string_key”]

reference_a_hash = some_hash[23]

Question 45

what do you call the equivalent of a dictionary in Ruby?

Answer 45

a Hash

Question 46

difference between String.chomp and String.strip?

Answer 46

chomp gets rid of whitespace at the end, strip gets rid of leading and trailing white space

Question 47

do ruby methods need a return statement?

Answer 47

no. they will automatically return the last statement in the method if no return is provided

Question 48

How do we represent infinity in ruby?

Answer 48

-Float::INFINITY

and

Float::INFINITY

Question 49

what class does every class created by Ruby or a user inherit from?

Answer 49

the Object class

Question 50

what is a deep copy and how can we avoid them if desired?

Answer 50

a deep copy is when one variable is assigned to another, and then modifying one of those variables also modifies the other.

most common example is with arrays

[114] pry(main)> a = (0…10).to_a
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[115] pry(main)> b = a
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[116] pry(main)> a.pop
=> 9
[117] pry(main)> a
=> [0, 1, 2, 3, 4, 5, 6, 7, 8]
[118] pry(main)> b
=> [0, 1, 2, 3, 4, 5, 6, 7, 8]

we can avoid this with the .dup method:

[119] pry(main)> a = (0…10).to_a
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[120] pry(main)> b = a.dup
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[121] pry(main)> b
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[122] pry(main)> a.pop
=> 9
[123] pry(main)> a
=> [0, 1, 2, 3, 4, 5, 6, 7, 8]
[124] pry(main)> b
=> [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[125] pry(main)>

Question 51

difference between p, puts, print

Answer 51

p and puts includes a new line character, print does not.

p prints the “quotes”, good for debugging so it is clear if something is a string or not (example an integer)

Question 52

how do we make a class variable and how does it work?

Answer 52

using @@ syntax

this variable is shared across all instances of the class, the value is the same across all sintances and changing the value in on instance changes it in all the others

Question 53

what is a Hash in ruby?

Answer 53

it is like a dictionary

Question 54

what do methods with a ! or an ? at the end do?

Answer 54

? simply indicates that a true or false will be returned

! indicates that this is a “dangerous method”, basically it will modify the object it is called on, instead of simply outputing a result of the method being called on the object

Question 55

when doing a begin and rescue, what is the difference between using p and puts for the error?

Answer 55

puts will just give the contents of the raise statement as defined by the script

p will give you the full error type and message generated by ruby

Question 56

what expression can you use as a shortcut for .push on an Array?

Answer 56

<<

Question 57

inside #{} what can be written?

Answer 57

any ruby code at all, it will be executed and whatever it returns is printed as a string where the #{} was

Question 58

what is the inverse of #select?

Answer 58

#reject

Question 59

How do you work with the Hash#each block?

Answer 59

meals = {
breakfast: “oats”,
lunch: “curry”,
dinner: “ramen”
}

meals.each do |key, value|
puts value
end

Question 60

how can you do an each over just a range of indexes?

Answer 60

just put a range in the index like so:

start_index = train_line.stops.find_index { |stop| stop[:name] == station_start }
finish_index = train_line.stops.find_index { |stop| stop[:name] == station_finish }
stops = []
train_line.stops[start_index..finish_index].each do |stop|
stops << stop[:name]
end

Question 61

what does This::Syntax mean?

e. g.
* robot = ToyRobot::Robot.new*

Answer 61

it the Syntax class from the This module

e.g.

*module ToyRobot
 class Robot
 attr\_reader :north, :east, :facing*

def initialize(north = 0, east = 0, facing = “north”)
@north = north
@east = east
@facing = facing
end

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