Ruby Monstas

What is a loop

A loop repeats code until we tell it to stop

http://gph.is/1vnWBtS

A simple loop

We can declare a loop with loop do ... end

counter = 0

loop do
  puts "#{counter} seconds since the loop started"
  sleep(1) # waits for 1 second
  counter = counter + 1
end

0 seconds since the loop started
1 seconds since the loop started
2 seconds since the loop started
3 seconds since the loop started
...

Problem: This runs forever

Stopping the loop

We use the keyword break to stop a loop

counter = 0

loop do
  puts "#{counter} seconds since the loop started"
  sleep(1)
  counter = counter + 1

  if counter == 2
    break # "breaks" the loop
  end
end

puts "Now we're here..."

0 seconds since the loop started
1 seconds since the loop started
Now we're here...

Main rule

Every loop should have a break!

...else we have an infinite loop!

Summary

loop do
  # the lines between "loop do" and "end"
  # get repeated until we
  # break it

  if condition
    break
  end         # this "end" belongs to the if-statement
end           # this "end" belongs to loop do

Additional Resources

Loops and Iterators

What questions do you have?