# Iterationer och slingor

So far we’ve spent a lot of time looking at the different sounds you can make with `play` and `sample` blocks. We’ve also learned how to trigger these sounds through time using `sleep`.

As you’ve probably found out, there’s a lot of fun you can have with these basic building blocks. However, a whole new dimension of fun opens up when you start using the power of code to structure your music and compositions. In the next few sections we’ll explore some of these powerful new tools. First up is iteration and loops.

## Repetition

Have you written some code you’d like to repeat a few times? For example, you might have something like this:

    play 50
    sleep 0.5
    sample :elec_blup
    sleep 0.5
    play 62
    sleep 0.25

What if we wished to repeat this 3 times? Well, we could do something simple and just copy and paste it three times:

    play 50
    sleep 0.5
    sample :elec_blup
    sleep 0.5
    play 62
    sleep 0.25
    play 50
    sleep 0.5
    sample :elec_blup
    sleep 0.5
    play 62
    sleep 0.25
    play 50
    sleep 0.5
    sample :elec_blup
    sleep 0.5
    play 62
    sleep 0.25

Now that’s a lot of code! What happens if you want to change the sample to `:elec_plip`? You’re going to have to find all the places with the original `:elec_blup` and switch them over. More importantly, what if you wanted to repeat the original piece of code 50 times or 1000? Now that would be a lot of code, and a lot of lines of code to alter if you wanted to make a change.

## Iteration

In fact, repeating the code should be as easy as saying do this three times. Well, it pretty much is. Remember our old friend the code block? We can use it to mark the start and end of the code we’d like to repeat three times. We then use the special code `3.times`. So, instead of writing do this three times, we write `3.times do` - that’s not too hard. Just remember to write `end` at the end of the code you’d like to repeat:

    3.times do
      play 50
      sleep 0.5
      sample :elec_blup
      sleep 0.5
      play 62
      sleep 0.25
    end

Now isn’t that much neater than cutting and pasting! We can use this to create lots of nice repeating structures:

    4.times do
      play 50
      sleep 0.5
    end
    8.times do
      play 55, release: 0.2
      sleep 0.25
    end
    4.times do
      play 50
      sleep 0.5
    end

## Nesting Iterations

We can put iterations inside other iterations to create interesting patterns. For example:

    4.times do
      sample :drum_heavy_kick
      2.times do
        sample :elec_blip2, rate: 2
        sleep 0.25
      end
      sample :elec_snare
      4.times do
        sample :drum_tom_mid_soft
        sleep 0.125
      end
    end

## Looping

If you want something to repeat a lot of times, you might find yourself using really large numbers such as `1000.times do`. In this case, you’re probably better off asking Sonic Pi to repeat forever (at least until you press the stop button!). Let’s loop the amen break forever:

    loop do
      sample :loop_amen
      sleep sample_duration :loop_amen
    end

The important thing to know about loops is that they act like black holes for code. Once the code enters a loop it can never leave until you press stop - it will just go round and round the loop forever. This means if you have code after the loop you will never hear it. For example, the cymbal after this loop will never play:

    loop do
      play 50
      sleep 1
    end
    sample :drum_cymbal_open

Now, get structuring your code with iteration and loops!