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Question 1

Explain the following code:

arry[1..6]

Answer 1

Returns the 2nd through 7th elements of the ‘arry’ array

Question 2

What is the difference between [2..4] and [2…4]

Answer 2

Three periods is not inclusive of the last element; two periods is.

Question 3

Explain the following code:

arry[2..-1]

Answer 3

Returns the third through the last element of the array.

Question 4

T/F: Never modify an array while iterating through it.

Answer 4

T; You can get stuck in an infinite loop

Question 5

What is an advantage of Array#concat?

Answer 5

It modifies the first array by including references to the second array; very little memory cost.

Question 6

Explain Array#include? and Array#index

Answer 6

include? returns a Boolean for finding the argument, #index returns the index of the element as an integer or nil if it is not found.

Question 7

Explain the array methods:
#sort, #sort!, #shuffle, #sample

Answer 7

sort sorts an array, with the smallest element at index 0

Question 8

T/F: It doesn’t matter if arrays are heterogeneous (contain more than one type)

Answer 8

F; They can, but should be homogenous whenever possible.

Question 9

Y/N: Will the following code execute?

“this is my sentence”[5, 2]

Answer 9

Yes; when given arguments like [int, int], the first argument is the starting index of the substring and the second argument is the length of the substring. For this reason, the code returns “is”

Question 10

Explain the following string methods: #strip, #chomp, #gsub

Answer 10

strip removes leading and trailing whitespace

Question 11

When a hash is used with an enumerable, what gets passed to the block?

Answer 11

|key, value|

Question 12

When merging hashes with #merge, what will happens when a key is shared but each hash has a different value for the key?

Answer 12

The hash which is being merged (the argument) into the other hash takes precedence.

Question 13

What is a quick way to check if a hash has a key?

Answer 13

has_key?

Question 14

What is the difference between Enumerable#each and Enumerable#map (also known as Enumerable#collect)? When should you use them?

Answer 14

each returns the original UNMODIFIED array, while #map returns a new array with the computed values.

Use #each when you only want the method’s side-effects; use #map when you want to use the returned (computed) values.

Question 15

Explain Enumerable#inject

Answer 15

We pass inject an initial value and a block. The code block takes the current accumulator value and the next element in the Enumerable . The block is run, and the accumulator value is updated with the block’s result. When all elements have been processed, the accumulator value is returned.

nums = [1, 2, 3, 4, 5]
nums.inject(0) do |accum, element| # accum is initially set to 0, the method argument
accum + element
end

This code returns 15 (the sum of all the elements)

Question 16

Explain Enumerable#select and Enumerable#count

Answer 16

select returns an array consisting of elements from the enumerable for which the given code block returns true.

Question 17

What is the difference between Enumerable#include?, Enumerable#any?, Enumerable#all?, and Enumerable#none?

Answer 17

include? returns true if the argument is equal to any item in the collection.

The other 3 methods work similarly. #any? returns true if at least one element of the collection returns true given the code block, while #all? checks if all elements return true and #none? checks if all elements return false.

Question 18

What is the difference between Kernel#puts and Kernel#p ?

Answer 18

puts calls #to_s, whereas #p calls #inspect

Question 19

T/F: The following code returns true:

nil.nil?

Answer 19

T; this is the only case where this will happen.

Question 20

What methods can be used to check the type of an object?

Answer 20

class and #is_a?(datatype)

Question 21

What happens if you do not overload #== for a class you define?

Answer 21

It will always return false, unless you are comparing an object to itself.

Question 22

What is “technical debt”

Answer 22

Code can become unwieldy when there is a rush for a deadline, so you can take out technical debt by working with “smelly” code and refactoring at another time, although remember that this is a delicate balance; debt can catch up with you!

Question 23

How can we use the byebug debugger?

Answer 23

Add ‘require ‘byebug’’ to the top of your file, then insert the ‘debugger’ keyword where you want your breakpoint(s).

Question 24

How can we add a breakpoint within byebug?

Answer 24

$break linenum

Question 25

What is the byebug command to view the stack trace?

Answer 25

$wtf

Question 26

What is the difference between ‘next’ and ‘step’ in byebug?

Answer 26

‘next’ executes the line and advances to the next line, while ‘step’ steps into the code and follows its execution. Type ‘finish’ to get out of the step.

Question 27

What do ‘display’ and ‘where’ do in byebug?

Answer 27

‘display’ watches the value of the variable (given as an argument), and ‘where’ displays the call stack.

Question 28

Explain the following error messages:

NameError

Uninitialized Constant

NoMethodError

ArgumentError

TypeError

LoadError

SyntaxError

Answer 28

A NameError exception is thrown when you try to use a variable or method that hasn’t been defined.

“Uninitialized constant” means that Ruby is trying to find a class (or other constant), but didn’t find it.

NoMethodError is thrown when a method or variable that does not exist/ can’t be located is called

ArgumentError is for the wrong number of arguments

A TypeError may be thrown if you pass the wrong type of thing to a method.

A LoadError occurs when a file is attempted to be loaded into a program but cannot be found.

Writing ungrammatical Ruby code will net you a SyntaxError . This tells you that Ruby didn’t understand your code.

Question 29

The typical source file contains how roughly how many lines of code and how many classes?

Answer 29

1 class and less than 300 lines.

Question 30

When using the ‘require’ keyword with our own files, what must be added to the beginning of the filename?

Answer 30

’./’

Question 31

What is the difference between a library file and a script file?

Answer 31

Some Ruby source files contain definitions of classes and methods meant to be loaded by other Ruby code (called library files), while others are intended to be executed as a program (called script files).

Question 32

What is the guard to add conditional execution to a file?

Answer 32

if $PROGRAM_NAME == __FILE__
scriptactions
end