Intro to Ruby

Question 1

What type of language is Ruby?

Answer 1

High-Level: looks more like english; closer to human language than computer language

Interpreted: An interpreter produces results while the program is executing, as opposed to a compiled language that is translated to machine code prior to running / Interpreted slower than Compiled

Object-Oriented: encapsulation, abstraction, polymorphism, inheritance

Question 2

Data Types in Ruby

Answer 2

Arrays, Booleans, Hashes, Numbers, Strings, Symbols

Question 3

Array

Answer 3

A collection of objects. Can be strings, numbers, other arrays, etc.

Created by enclosing objects in square brackets
[“x”, “y”, “z”]

Indexing starts with zero

Question 4

Is Ruby case sensitive?

Answer 4

Yes

Question 5

Variable

Answer 5

Variables are ‘named’ storage locations for values.

We DECLARE variables and ASSIGN them values by using the assignment operator: =

Question 6

Ruby Arithmetic Operators

Answer 6

Addition: +
Subtraction: -
Multiplication: *
Division: /
Exponentiation: **
Modulo: %  (gives remainders of division)

Question 7

‘print’ and ‘puts’ commands

Answer 7

The ‘print’ command simply prints to the screen. Successive ‘print’ commands will print on same line.

The ‘puts’ command (short for put string) is similar but it will go to a new line after the value is printed.

Question 8

Classes, Objects and Methods

Answer 8

Classes are high-level TYPES/CATEGORIES of things (e.g. Houses)

Objects are things that are specific INSTANCES of types (e.g. a specific House -> BJ House)

Methods act on objects. They’re an Expression that returns a value (e.g. Paint Blue the BJ House)

Question 9

Methods

Answer 9

Methods implement the functionality of your program.

Methods are expressions or messages sent to the object that cause it to respond in a manner specific to the method instruction; instead of “calling a method”, Rubyists say “send a message” to the object

http: //ruby-for-beginners.rubymonstas.org/objects.html (best site)
http: //ruby-for-beginners.rubymonstas.org/writing_methods/definition.html

Question 10

Predicate Methods

Answer 10

methods that end with a ?.

they Result in (return) true or false, (return Boolean). Ex.:

5.odd?
=> true

5.between(11, 20)
=> false

Question 11

Bang Methods

Answer 11

methods that end with an !. They MODIFY the object they are called on. For example:

my_name = "Billy Jenkins"
puts my_name.upcase
    => BILLY JENKINS    (then..)
puts my_name
    => Billy Jenkins (same as original assignment)

However,
puts my_name.upcase!
    => BILLY JENKINS      (then..)
puts my_name
    => BILLY JENKINS

Question 12

Methods and Variables

Answer 12

Just as Variables are used to assign a name to an object, a Method is a way of assigning a name to a small executable piece of code

Variables name THINGS, Methods name BEHAVIOR

Question 13

Structure of a Method

Answer 13

def gimme_bacon()
puts “Bacon plz.”
end

The def keyword is Ruby syntax that we want to DEFine a method
next, gimme_bacon is the Method NAME
next, the Method’s arguments in ( )
next, ‘puts “Bacon plz.” is the Method BODY
next, end marks the END of the Method

def add_two(number)
number + 2
end

https://ruby-doc.com/core/doc/syntax/methods_rdoc.html

Question 14

.length

Answer 14

return value is the number of characters in a string

https://ruby-doc.org/core-2.2.0/String.html

Question 15

.reverse

Answer 15

return value is the backwards (reverse) version of the string object

Question 16

.upcase

Answer 16

return value is the string is all UPPERCASE

Question 17

.downcase

Answer 17

return value is the string is all lowercase

Question 18

Single-Line Comments

Answer 18

use the # symbol
#this is a single line comment

Question 19

Multi-Line Comments

Answer 19

use =begin and =end
=begin
this is a 
multi-line comment
=end

** =begin and =end need to be on their own lines

Question 20

Variable Naming Convention

Answer 20

should start with lowercase letter

word should be separated by an underscore

e.g., my_first_bicycle_model

Question 21

Chaining Methods

Answer 21

object.method1.method2.method3
Example
name = “Bill Jenkins”
puts name.downcase.reverse.upcase

return value => SNIKNEJ LLIB

Question 22

.gets

Answer 22

Ruby methods that obtains information from the user

can be stored in a variable

Question 23

How to print a variable inside of a string

Answer 23

Must be inside quotes
Must use # and { }
e.g. my_name = “Billy Jenkins”
print “My name is #{my_name}.”

Question 24

.capitalize

Answer 24

capitalizes the first letter of the string

Question 25

if / elsif / else

Answer 25

the if and elsif statement test whether an expression evaluates to true or false; if true, it executes the following line of code. if false, it moves on to the next elsif or else

• must finish if/elsif statements with “end”

Question 26

unless

Answer 26

The unless statement is best for checking if something is false, rather than true. For example:

print “How are you feeling? “
user_state = gets.chomp

unless user_state == "Hungry"
  puts "I'm writing Ruby programs!"
else
  puts "Time to eat!"
end

Question 27

==

Answer 27

The double equal sign is always used to test whether to values are equal

A single equal sign (=) is used for assignment, not evaluation

Question 28

!=

Answer 28

Not equal

Question 29

Comparators (or Relational Operators)

Answer 29

==, !=, , <=, >=

Question 30

Logical Operators (or Boolean Operators)

Answer 30

&& (and), | | (or), and ! (not)

&& - both must be true to evaluate to true
| | - one must be true to evaluate to true
! - changes true to false and false to true

Question 31

.include? method

Answer 31

Returns true if String or String Variable contains the given string or character.

user_input = “Yes, please.”
if user_input.include? “s” (would evaluate to true)

Question 32

.gsub! method

Answer 32

Global SUBstitution method every instance of the first argument with the contents of the second argument

The syntax looks like this:
string_to_change.gsub!(/s/, “th”)

https://ruby-doc.org/core-2.2.0/String.html