Branching units split the control flow based on a value.


The common branch unit uses a boolean condition. You can think of them as an if the condition is true, do something, else, do something else.


You can also branch depending on the value of an enum, a string or an integer. These units are called Switch units, like they are in scripting. 

To switch on an enum, you first need to decide the type of the enum. This will make the branch output ports appear: 

To switch on a string or number, you first need to create each branch option in the graph inspector:

The unit will then be updated with each output port:

For strings, you can optionally choose to ignore the case of the selector.

Note that a Default port is always added. It is the path that the control flow should take if the input selector does not correspond to any other option.


Select units are the opposite of switch units. They allow you to select a single value from a set of options based on a selector.

Because they're so similar, we're not going to cover each of them, but here's an example of a Select On Integer unit that chooses a color based on a player number:

Note that predictive debugging here warns you that there will be a crash if playerNo is not within 1, 2, 3, or 4, because we haven't connected the Default port. If we're sure that it never will be for example 5 or 6, we can safely ignore this warning.


Loops allow you to repeat logic for a certain number of iterations before moving on.

The logic to be repeated is called the body of the loop. After the loop is over, the exit port is called.

Note that the body of every loop is called synchronously, not over the course of multiple frames. Coroutine-like behaviours are instead achieved by listening to the update event manually.

While Loop

While is the simplest form of loop. It will repeat its body while its condition remains true, or in other words, until it becomes false.

For example, this graph generates a new random name until the result isn't contained in the names application variable:

Be careful not to create an infinite loop! If the condition is always true, the editor will hang. Because loop bodies are synchronous, not parallel, there are few uses for while loops in Bolt. 

For Each Loop

For Each iterates over every element of a collection. It outputs the current index and item that is being looped over.

For example, this graph will output 3 messages to the console:

  • I like cats
  • I like dogs
  • I like birds

To access the key and value from dictionaries in the loop, check the Dictionary box:

For Loop

For is a numeric loop. It requires 3 integers: a start index, an end index, and a step. The loop will start at the first index, then move towards the last index via increments of the step. It outputs the current index.

For example, this graph will count to ten by skipping odd numbers because of its step. In other words, its output will be 0, 2, 4, 6, then 8.

The for loop can also be very useful when combined to the Get List Item and Count Items units.

For example, this graph is very similar to the last, in that it will output I like {animal}s to the console. However, instead of using the for each unit that outputs each item, we get each item manually by its index in the list. This allows us to specify a different increment (in this case 2) and skip some items. Therefore, this graph will only output 2 messages:

  • I like cats
  • I like birds

Break Loop

You can tell a loop to finish early by using the Break Loop unit. As soon as this unit is entered, the exit port of the loop will be called, no matter how many more iterations remained.

For example, even though this for loop is supposed to count to 10, it will stop at 5 because of the break. Therefore, its output will be 0, 1, 2, 3, then 4.

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having a difficult time with "while" loop. Can you provide another (much simpler?) example?

Hi Ikol! The while loop is useful in some cases, but often it doesn't do what we think when we think of "while". If you want to execute the same code each frame while some condition is true, just connect a Branch unit to the Update event. There is also Wait While and Wait Until units that allows to delay execution until a condition becomes true or false.

It all depends: what are you trying to do?

oh, so that's why. whew, thanks a bunch Lazlo. I thought I was going insane. trying to make a progress bar for a clicker game (there's enough of it, I know), and I kept getting stuck on an infinite loop.

Can you confirm that the For loop will never iterate the 'Last' index, but only up to Last-1 ? It's a bit confused in the text above as it twice mentions 'count to 10' , but in fact will only ever get to 9 ? 

Yes, for loops are inclusive for start, exclusive for end.