Ruby Loops and Iterators

Codecademy Cheatsheet

Ruby while Loop

Putting a block of code in a while loop in Ruby will cause the code to repeatedly run the code as long as its condition is true.

If the block of code doesn’t have a way for the condition to be changed to false, the while loop will continue forever and cause an error.

i = 1

while i <= 3 do
  puts "Message number #{i}"
  i = i + 1
end

# Output:
# Message number 1
# Message number 2
# Message number 3

The 'Until' Loop

Putting a block of code inside an until loop in Ruby will cause the code to run as long as its condition remains false. It’s only when the condition becomes true that the loop stops.

If the block of code doesn’t allow for a way for the condition to be changed to true then the loop will continue forever and it will cause an error.:

i = 0
until i == 6
  i = i + 1
end
puts i

Ruby Assignment Operators

Assignment operators in Ruby are used to assign or update values to variables. The most common assignment operator is = but others also exist, like +=, -=, *= and /=.

a = 1;
a += 3;
puts a; # Output: 4

b = 4;
b -= 2;
puts b; # Output: 2

num = 12;
num *= 2;
puts num; # Output: 24

num /= 4;
puts num; # Output: 6

Ruby for Loop

A block of code can be repeated a set amount of times with the for loop in Ruby.

for i in 1..3 do
  puts "Message number #{i}"
end

# Output
# Message number 1
# Message number 2
# Message number 3

Inclusive and Exclusive Ranges

for num in 1...10. What this says to Ruby is: “For the variable num in the range 1 to 10, do the following.” The following was to puts "#{num}", so as num took on the values of 1 to 9, one at a time, those values were printed to the console.

The reason this program counted to 9 and not 10 was that we used three dots in the range; this tells Ruby to exclude the final number in the count: for num in 1...10 means “go up to but don’t include 10.” If we use two dots, e.g. for num in 1..10, this tells Ruby to include the highest number (10) in the range.

Ruby loop

A loop method can be used to run a block of code repeatedly in Ruby. Either use curly braces ({}) or the do/end keyword combination to wrap the block of code that will be looped.

iterator
An iterator is just a Ruby method that repeatedly invokes a block of code. The code block is just the bit that contains the instructions to be repeated, and those instructions can be just about anything you like!

num = 1
loop do
  puts "We are in the loop!"
  num += 1
  break if num > 3
end

puts "We have exited the loop!"

# Output
# We are in the loop!
# We are in the loop!
# We are in the loop!
# We have exited the loop!

The break keyword is our Get Out of Jail Free card: it breaks a loop as soon as its condition is met.

Next!
In Ruby, the next keyword is used within a loop to pass over certain elements and skip to the following iteration. It is useful for omitting elements that you do not wish to have iterated. next is followed by an if statement which defines which elements are to be skipped.

for i in 1..5
  next if i % 2 == 0
  print i
end

i = 20
loop do
  i -= 1
  next if i % 2 == 1
  print "#{i}"
  break if i <= 0
end

array

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

Ruby each Method

To iterate over an array in Ruby, use the .eachmethod. It is preferred over a for loop as it is guaranteed to iterate through each element of an array.

object.each { |item| 
  # Do something 
}

You can also use the do keyword instead of {}:

object.each do |item| 
  # Do something 
end

data = [3, 6, 9, 12]

data.each do |num|
  puts "The number is: #{num}"
end

# Output:
# The number is: 3
# The number is: 6
# The number is: 9
# The number is: 12

The .times Iterator
The .times method is like a super compact for loop: it can perform a task on each item in an object a specified number of times.

For example, if we wanted to print out "Chunky bacon!" ten times, we might type

10.times { print "Chunky bacon!" }

Examples:

i = 1
while i <= 50
  print i
  i -= 1
end

i = 1
until i == 50 do
print i
i += 1
end

for i in 1..50
print i 
i += 1
end

m = 0
loop do 
m += 1
print "Ruby!"
break if m >= 30
end

puts "Text to search through: "
text = gets.chomp
puts "Word to redact: "
redact = gets.chomp

words = text.split(" ")

words.each do |word|
  if word != redact
    print word + " "
  else
    print "REDACTED "
  end
end