Ruby On Rails

Question 0

Ask name & print “Hello, _____!”

Answer 0

print “What’s your name ?”
name = gets.chomp
p “Hello, #{name}!”

Question 1

\t

\s

Answer 1

tab in Ruby. ie. “Bob\tDoe” prints
“Bob Doe”

space in Ruby ie. “Bob\sDoe” prints
“Bob Doe”

Question 2

.split

Answer 2

divides string into substrings, returning an array of these substrings. ie:
“ now’s the time”.split #=> [“now’s”, “the”, “time”]
“ now’s the time”.split(‘ ‘) #=> [“now’s”, “the”, “time”]
“ now’s the time”.split(/ /) #=> [””, “now’s”, “”, “the”, “time”]
“1, 2.34,56, 7”.split(%r{,\s}) #=> [“1”, “2.34”, “56”, “7”]
“hello”.split(//) #=> [“h”, “e”, “l”, “l”, “o”]
“hello”.split(//, 3) #=> [“h”, “e”, “llo”]
“hi mom”.split(%r{\s}) #=> [“h”, “i”, “m”, “o”, “m”]

“mellow yellow”.split(“ello”) #=> [“m”, “w y”, “w”]
“1,2,,3,4,,”.split(‘,’) #=> [“1”, “2”, “”, “3”, “4”]
“1,2,,3,4,,”.split(‘,’, 4) #=> [“1”, “2”, “”, “3,4,,”]
“1,2,,3,4,,”.split(‘,’, -4) #=> [“1”, “2”, “”, “3”, “4”, “”, “”]

Question 3

«HERE
(HERE document)
Great for adding large sets of text.

Answer 3

Ie. words = <<HERE
     Now is the time
     for all people
     to come together.
HERE

print words
Now is the time
for all people
to come together.

Question 4

.include?

Answer 4

Does something include?
Ie. letters = ‘a’..’z’
letters.include?(‘h’)
=> true

Question 5

.squeeze

Answer 5

Removes trailing spaces.
Ie. name = “Jane “
name.squeeze returns “Jane “

Question 6

.each

Answer 6

Will return each piece of data within object called.
Ie. range = (0..4)
range.each {|n| puts n}
0
1
2
3
4

Question 7

.to_a

Answer 7

Turns data into an array.
Ie. digits = 0..3
num_array = digits.to_a
=> [0, 1, 2, 3]

Question 8

$ variables

Answer 8

$ makes variable global

Ie. $salary = 40000

Question 9

hash = {}

Answer 9

Holds keys with values
Ie. nums = {
'Dave' => '1234',
'Bill' => '2345'
}
nums['Dave']
=> "1234"
OR new way is
Dave: 1234,
Bill: 2345
Nums[:Dave]
=> 1234

Question 10

Constants

Answer 10

Variable in all uppercase:

PI = 3.14

Question 11

.to_s

Answer 11

Converts data to string
Ie. age = Integer(gets)
puts “Being “ + age.to_s + “ feels just like “ + (age-1).to_s + “!”

Question 12

.rand

Answer 12

Randomizer
Ie. nums = []
i = 0
while i < 5
nums[i] = .rand(101)
i += 1
End

Question 13

Parallel assignment

Answer 13

a, b = b, a

This will swap the values of the variables. Nice to use with data sorting w/o introducing new variable.

Question 14

defined?

Answer 14

Defines data:
Ie. a = 1
defined? a
=> “local-variable”

Question 15

.step

Answer 15

Use to “step” values. Ie. if step = 5, values will be incremented by 5.

0.step(15,5) {|i| print i, “ “ }
=> 0 5 10 15

Question 16

case (when)

Answer 16

Useful "when" there's lots of data. Otherwise if/else statement is better.
Ie:
puts("Enter a grade: ")
grade = gets
grade = Integer(grade)
case grade
   when 90..100
      letterGrade = "A"
   when 80..89
      letterGrade = "B"
   when 70..79
      letterGrade = "C"
   when 60..69
      letterGrade = "D"
   else 
      letterGrade = "F"
end
puts("The letter grade is " + letterGrade)

Question 17

break

use cautiously

Answer 17

Ends program if activated and/or will go to next line program after final end if there is one.
Ie:
if data/input == 0 then
     break
end
#next line

Question 18

redo

Answer 18

Restarts program if activated.
Ie:
if data/input == 0 then
     redo
end

Question 19

next

Answer 19

Jumps to next iteration of the most internal loop. Terminates execution of a block if called within a block (with yield or call returning nil).

for i in 0..5

if i < 2 then

  next    end    puts "Value of local variable is #{i}" end

Question 20

exit

Answer 20

Exits program. Ie:
elsif tries == 3
puts "Sorry answer is apple."
exit
else 
puts "Try again."

Question 21

require

Answer 21

Includes or “requires” the use of the named file:

require ‘./tempconvert’

puts ftoc(212)
puts ctof(0)

Question 22

rescue

Answer 22

Provides solution to an exception “error.” Ie. if you try and divide by zero.
Needs “begin”, “rescue” & “end”

begin
   print("Enter numerator: ")
   num = Integer(gets)
   print("Enter denominator: ")
   denom = Integer(gets)
   ratio = num / denom
   print(ratio)
rescue
   print $! #this stores the exception
   puts
   print("Enter a denominator other than 0: ")
   denom = Integer(gets)
   ratio = num / denom
   print(ratio)
end

Question 23

Debug

Answer 23

(In terminal)

ruby -r debug file.rb

Question 24

variable

Answer 24

storage location/s that hold data used by program

Question 25

.slice

Answer 25

If passed a single index, returns a substring of one character at that index. If passed a start index and a length, returns a substring containing length characters starting at the index. If passed a range, its beginning and end are interpreted as offsets delimiting the substring to be returned. ie:
a = "hello there"
a[1]                   #=> "e"
a[2, 3]                #=> "llo"
a[2..3]                #=> "ll"
a[-3, 2]               #=> "er"
a[/[aeiou](.)\1/, 0]   #=> "ell"
a[/(?[aeiou])(?[^aeiou])/, "non_vowel"] #=> "l"

Question 26

.count

Answer 26

used to count characters. ie:
a = "hello world"
a.count "lo"                   #=> 5
a.count "lo", "o"              #=> 2
"hello^world".count "\\^aeiou" #=> 4

c = “hello world\r\n”
c.count “\” #=> 2

Question 27

.sub

Answer 27

substitutes ONLY the first occurrence of the pattern specified, whereas gsub is “global”. (see gsub card for examples)

Question 28

.gsub

Answer 28

global substitution method. ie:
“hello”.gsub(/[aeiou]/, ‘’) #=> “hll”
“hello”.gsub(/([aeiou])/, ‘’) #=> “hll”
“hello”.gsub(/./) {|s| s.ord.to_s + ‘ ‘} #=> “104 101 108 108 111 “
“hello”.gsub(/(?[aeiou])/, ‘{\k}’) #=> “h{e}ll{o}”
‘hello’.gsub(/[eo]/, ‘e’ => 3, ‘o’ => ‘’) #=> “h3ll*”

“Super guper bag”.gsub “g”, “d” # => “Super duper bad”
“Ruby is 13%”.gsub( ‘%’ ) {|c| c.ord.to_s + ‘ ‘ } # => “Ruby is 1337”

Question 29

.replace

Answer 29

Replaces the contents and taintedness of str with the corresponding values in other_str.

s = “hello” #=> “hello”
s.replace “world” #=> “world”

Question 30

.scan (array or block)

Answer 30

Array:
a = “cruel world”
a.scan(/\w+/) #=> [“cruel”, “world”]
a.scan(/…/) #=> [“cru”, “el “, “wor”]
a.scan(/(…)/) #=> [[“cru”], [“el “], [“wor”]]

Block:
a = "cruel world"
a.scan(/\w+/) {|w| print "<> " }
print "\n"
=> <> <>
a.scan(/(.)(.)/) {|x,y| print y, x }
print "\n"
=> rceu lowlr

Question 31

.strip

Answer 31

strips whitespace. ie:
“ hello “.strip #=> “hello”
“\tgoodbye\r\n”.strip #=> “goodbye”

Question 32

.floor

Answer 32

The .floor method rounds a float (a number with a decimal) down to the nearest integer.

Question 33

.upto

Answer 33

iterates thru successive values, returning those values. ie:
3.upto(10) {|x| print x, “ “} => 3 4 5 6 7 8 9 10
“9”.upto(“11”).to_a #=> [“9”, “10”, “11”]

Question 34

• ( *args) or splat argument

Answer 34

• tells Ruby that there could be more than 1 argument. ie:
  #in this example *args takes 3 arguments:
  def what_up(greeting, *args)
  args.each { |bro| puts “#{greeting}, #{bro}?” }
  end
  what_up(“What up”, “Justin”, “Ben”, “Kevin”)

=> What up, Justin?
What up, Ben?
What up, Kevin?

Question 35

proc (procedure)

Answer 35

http://ruby-doc.org/core-2.0/Proc.html

Question 36

yield

Answer 36

used to "invoke" a block. useful for passing arguments within a method. ie:
def double(number)
    yield(4)           => 8
    yield(8)           => 16
    yield(12)          => 24
    yield(number) => 12
end
double(6) { |n| puts "#{n * 2}"  }

Question 37

:: (scope resolution operator)

Answer 37

Tells Ruby where to look for a specific bit of code. If we say Math::PI, Ruby knows to look inside the Math module to get that PI, not any other PI.

Question 38

Domain

Answer 38

A domain is a field of study that defines a set of common requirements, terminology, and functionality for any software program constructed to solve a problem in the area of computer programming, known as domain engineering.

Question 39

inject

Answer 39

Combines all elements of enum by applying a binary operation, specified by a block or a symbol that names a method or operator.
# Same using a block and inject
(1..3).inject { |sum, n| sum + n }            #=> 6

# Same using a block
(5..10).inject(1) { |product, n| product * n } #=> 151200

Question 40

map

Answer 40

The map method can be used to create a new array based on the original array, but with the values modified by the supplied block:
arr = [1, 2, 3, 4, 5]
arr.map { |a| 2*a } #=> [2, 4, 6, 8, 10]
arr #=> [1, 2, 3, 4, 5]
#use of “!” is destructive
arr.map! { |a| a**2 } #=> [1, 4, 9, 16, 25]
arr #=> [1, 4, 9, 16, 25]

Question 41

CRUD

Answer 41

Create, Retrieve, Update, Delete