Ruby Basics

Question 1

literal

Answer 1

Any notation that lets you represent a fixed value

‘Hello, world!’ // string literal
375 // integer literal
3.141528 // float literal
true // boolean literal
{ ‘a’ => 1, ‘b’ => 2 } // hash literal
[ 1, 2, 3 ] // array literal
:sym // symbol literal
nil // nil literal

Question 2

string

Answer 2

list of characters in a specific sequence
written with either single or double quotes
if using single quotes, then single quotes within the text are indicated with escaping: ‘The man said, 'Hi there !' ‘
double quotes allow string interpolation

Question 3

:symbol

Answer 3

indicated with leading “:”
Used to reference something like a string, but don’t intend to print to screen or change.
Referred to as immutable, although that’s not technically correct

Question 4

numbers

Answer 4

Integer (whole numbers)

Float (with decimals)

Question 5

nil

Answer 5

indicates “nothing”

can check for nil with .nil?

Question 6

modulo, remainder, divmod

Answer 6

Return either modulus or an array containing the quotient and modulus
num.divmod(numeric) → [quotient, modulus]
num % divisor → remainder
num.remainder(numeric) → remainder

a	b	a % b (modulo)	a.remainder(b)	a.divmod(b)
17	5	2	2	[3, 2]
17	-5	-3	2	[-4, -3]
-17	5	3	-2	[-4, 3]
-17	-5	-2	-2	[3, -2]

Question 6

modulo, remainder, divmod

Answer 6

Return either modulus or an array containing the quotient and modulus
num.divmod(numeric) → [quotient, modulus]
num % divisor → remainder
num.remainder(numeric) → remainder

a b a % b (modulo) a.remainder(b) a.divmod(b)
17 5 2 2 [3, 2]
17 -5 -3 2 [-4, -3]
-17 5 3 -2 [-4, 3]
-17 -5 -2 -2 [3, -2]

Question 7

string.to_i

Answer 7

converts string to integer

Question 8

expressions and return

Answer 8

an expression always returns a value in Ruby, even if that value is nil or an error

Question 9

Variable Scope

Answer 9

Defined by where the variable is initialized or created. In Ruby, variable scope is defined by a method definition or by a block.
Inner scope can access variables initialized in an outer scope, but not vice versa.

When is a {} or do end piece of code not create a new scope?
When that code is part of the Ruby language, rather than a method.
Example: for I in arr {something} is not changing scope.
5.times { |x| something } is a method (times), and thus changes scope.

Question 10

Variable Types

Answer 10

Constants     All letters capitalized.  Can be changed, but Ruby will warn at run time.  Scope is global
Global          $var.  Are available throughout app, and override all scope boundaries.  Not typically used in Ruby. 
Class            @@var.  Available in a class and each instances. Not created within the class instance, but in the class.
Instance        @var.  Available in current instance of parent class.  Some can cross scope boundaries.
Local             Most common variable, lower case with _ separating words, not starting with symbol.

Question 11

method variables

Answer 11

Variables do not enter a method unless passed in, and do not leave unless returned.

Question 12

p
print
puts

Answer 12

print sends output with no additional spaces or line returns
puts sends output with a line return at the end
p sends output in the form the programmer wants to see it, e.g. with brackets, quotes etc., to help with validating that the output is in the form expected.

Question 13

call stack

Answer 13

call stack is the point in time: the methods, blocks, procs, and lambdas currently running
limited to 10,000 stack entries, will return “SystemStackError” if exceeded.

Question 14

Conditionals keywords and operators

Answer 14

If, else, elsif, end, and unless keywords

, <=, >=, ==, !=, &&, ||

Question 15

conditional syntax

Answer 15

if conditional
  action
elsif conditional
  action
else conditional
  action
end

if conditional then action end

action if conditional

Question 16

conditional operators and different data types

Answer 16

<=, , >= are not able to compare different types, e.g. ‘4’ and 4
== and != can compare strings and numbers

Question 17

comparison operator order of precedence

Answer 17

1. <=, , >=
2. ==, !=
3. &&
4. ||

Question 18

Ternary operator

Answer 18

conditional ? action if true : action if false

Question 19

case statement syntax

Answer 19

case 
when 
  action
when 
  action
else
  action
end

case
when condition
  action
when condition
  action
else
  action
end

Question 20

loop method

Answer 20

Simplest loop
loop do
action
end

-or-

loop { action }

Question 21

While loops

Answer 21

while condition
action
end

NOT a method, so no separate scope within the loop

Question 22

Until Loop

Answer 22

Until condition
action
end

NOT a method, so no new scope created within the loop.

Question 23

do / while loops

Answer 23

loop do
  action
  if condition
    break
  end
end

-eg-

loop do
  puts "Do you want to do that again?"
  answer = gets.chomp
  if answer != 'Y'
    break
  end
end

Question 24

for loops

Answer 24

No new scope when running

for x in y do
action
end

-e.g.-

x = [1, 2, 3, 4, 5]

for i in x.reverse do
puts i
end

puts “Done!”

Question 25

.each method

Answer 25

iterates over each element in a

Question 26

=~

Answer 26

Pattern matching or regex operator

use: “basketball” +~ /b/ will return 0 because the first b is in the 0 position