Fundamentals

Question 1

Variables

Answer 1

Plain, lowercase words consisting of letters, digits, and underscores.

Question 2

Numbers

Answer 2

Integers may contain underscores. So 12_000 ( twelve thousand) is valid. Floats may be written in decimal or scientific notation.

Question 3

String literals

Answer 3

Created by both single and double quotes.

Question 4

Symbols

Answer 4

words prefixed with a colon. Any valid variables is a valid symbol. They are like lightweight strings.

Question 5

Constants

Answer 5

Constants are invariable variables - they are Capitalized, and once set, cannot be changed.

Question 6

Method names

Answer 6

Generally appended via a dot ‘.’ to the end of a variable or constant. May contain bangs ‘!’ and question marks.

Question 7

Method arguments

Answer 7

follow a method name and are both surrounded by parens and delimited by commas.

Question 8

Class Methods

Answer 8

are appended – usually – to variables and constants. If so, they are appended via double colons, like so:

Door::new (:oak)

I.e., make a new oak Door.

Question 9

Global variables

Answer 9

Variables that begin with a $ are global.

Question 10

Instance variables

Answer 10

Variables that begin with an @ sign are instance variables – usually used to define the attributes of an object.

Question 11

Class variables

Answer 11

Variables that begin with TWO at signs – @@ – are class variables. They attribute to all the instances of the class.

Question 12

Blocks

Answer 12

Blocks are delimited by left and right curly braces. { }

The braces may be replaced by the keywords ‘do’ and ‘end’ for the left and right respectively.

Question 13

Block arguments

Answer 13

variables placed between pipe characters and delimited by commas are passed into the block. The block arguments are placed at the beginning (or top) of the block.

Question 14

Ranges

Answer 14

A range is denoted by two values enclosed by parens and separated by a two or three dot ellipsis. Ex:
(1..10) is the range one through nine.
(‘a’..’z’) is the range consisting of the lowercase letters.

NOTE: if two dots are used, the final value is inclusive.
if three dots are used, the final value is excluded.

Question 15

Array

Answer 15

An array is a list of things delimited by commas and wrapped in square brackets. It is ordered.

Question 16

Hashes

Answer 16

A hash is a dictionary surrounded by curly braces. The items are delimited by commas, and the relation is expressed with an Ascii arrow. Ex:

{ ‘this’ => ‘stuff’, ‘that’ => ‘other stuff’ }

Question 17

Regular expressions

Answer 17

In Ruby, regular expressions are wrapped in forward slashes. So /ruby/ is a regex that matches ‘ruby’, and /^\d{3}-\d{3}-\d{4}/ matches a phone number (note the enclosing forward slashes).

Question 18

Nil

Answer 18

is a value, but it is the empty value. It is NOT undefined. To say that a variable is undefined is to say Ruby has no cognition of the variable - to say it is Nil is to say it is empty.

variable = Nil
Empty, but not undefined.

Question 19

if

Answer 19

Two forms: it either wraps its code body like braces (if is the opening brace, ‘end’ is the closing brace) OR, if the code body is a single statement, may just be appended to the end as in
print “some stuff here” if stuff

Question 20

unless

Answer 20

Unless is like a negative if. It’s code is only executed if the expression evaluates Nil or false

Question 21

==

Answer 21

The double equal, like in most languages, checks identity. But it is actually a method. a == b is allowed as a shorthand for a.==( b )

Question 22

«

Answer 22

’<

Question 23

elsif

Answer 23

Ruby uses ‘elsif’ to mean javascripts ‘else if’ or Python’s ‘elif’. Remember all Ruby control statement blocks are ended by ‘end’.

Question 24

How do I check if a value is Nil?

Answer 24

The method ‘.nil?’ appended to the value to be checked.