annabellecat / kwk-l1-intro-to-loops-two-step-lab-kwk-students-l1-dfw-070918

Two Step and Repeat

This is a group lab, so make sure you are working in a group of 2-4 students

Have you ever seen a Two Step? It is not two steps! It is at least ten... maybe even twenty or thirty steps. And that's only if we stop dancing!

The trick to learning something like the Two Step along with most complex dances, is that a complicated dance is actually just made up of short, simple moves, repeating over and over, in a loop. Once you learn the simple moves, all you need to do is loop them together.

Let's learn some Two Step! We can use Ruby loops to help us out.

Part 1: The First Steps

In two_step_and_repeat.rb, Implement the first_steps method. This method should include a loop that outputs the following in your terminal endlessly, until you press ctrl+c.

puts "Right foot back"
sleep(0.5)
puts "Left foot back"
sleep(0.5)
puts "Right foot back"
sleep(0.5)
puts "Stop"
sleep(1)

If you haven't seen sleep(0.5) before, that's okay. This is a built in with Ruby and tells a program to stop for a moment. 0.5 is equal to one half second pause. The last sleep is set to pause for 1 second, giving us a moment to catch our breath before the loop starts over.

To see how this looks in your terminal, you can load up the two_step_and_repeat.rb file in IRB by entering the following in your terminal:

irb -r ./two_step_and_repeat.rb

Once you're in IRB, type in first_steps to start the loop. Use ctrl+c to get out and ctrl+d to close IRB. You'll have to run the line above each time your update your methods in order to see them in action.

Part 2: A Few More Steps

Wait... we're only going backwards! We need to at least turn. In the second Ruby method, we will expand our dance moves. Implement a_few_more_steps with a loop that includes all the steps from first_steps, but immediately after, outputs the following separated by sleep(0.5):

• "Right foot steps right and back"
• "Left foot crosses over right"
• "Right foot steps right"

Now we're moving... to the right! To finish this second set of moves, add one more puts, "Turn", followed by sleep(1).

Part 3: Just How Many Steps Do We Need To Take?

Our dance moves are great, but how many steps are we making in these endless loops? Well, it turns out, we can count in our loops using a variable. Inside how_many_steps?, implement the following:

• Create a variable called steps and set it equal to zero
• Just below this variable, write a loop that does four things:
  1. Increases the value of steps by 1
  2. Outputs the value of steps
  3. If the value of steps is divisible by 2 (remember how to use the %?), outputs 'Left', otherwise, it should output 'Right'
  4. Sleeps for 0.5 seconds

Make sure to take a look at the loop in your terminal to see if it is doing what you expect. This may require a number of.. steps.. so take your time and plan it out.

Part 4: Break Dancing

Okay, I think we need a break, and so do our loops. While infinite loops are cool, they aren't very useful because we have to tell them to stop looping. It is much better if our loops have some sort of conditional that, if true, exits the loop.

To do this, we can use the break command inside our loops. Using break stops everything in the loop block immediately. Anything below it will not be read:

# The following will only run until it hits 'break' on the first loop
loop do
  puts 'hello' # puts hello once
  break
  puts 'goodbye' # puts never fires
end

For this last method, we're going to be reusing some of our previous work, adding in a break to stop after a certain point.

1. Copy and paste your loop from the previous method into break_dance
2. At the bottom of the loop, add the following conditional: if steps is equal to 6, break.

If you've got the solution, this loop will display the following, then stop:

1
Right
2
Left
3
Right
4
Left
5
Right
6
Left

Summary

• Loops can be very useful for repeating steps in our code
• Loops will go on forever unless there is a way to tell them to stop
• We can write conditionals in our loops so that we can stop a loop once the conditional is found to be true

That's enough Two Step for now, but feel free to create your own loops, if you want! Try more complex patterns. For instance, you can try putting loops inside loops. Usually dances like the Two Step have a few beginning steps, followed by repetition of the same move two or three times, then a return to the beginning steps, repeating four or five times. This could be written as a loop that only fires three times inside a loop that fires five times.