$F >1 & $F <10

[Skybar]

Instead of keyframing something, I sometimes use $F >1 & $F <10 if I would want something to be active between frames 1-10. In my opinion it's just faster and easier than putting down a keyframe for certain things, like activating a fluid emitter, it's also easier to change it later if I would want to.

However, and this is where I have no clue. Say I would want the emitter to be active between frame 1-10, and then also 20-30. How do I do that? Is there a sign for OR, or something?

Like this: $F >1 & $F <10 OR $F >20 & $F <30

I've tried lots of variations with brackets and the &-sign in the middle (since that is the only thing I know of), but it obviously doesn't work since it all evaluates to 1-10 AND 20-30; and a frame can't be between both at the same time, making it impossible.

Does anyone know?

[graham]

OR is double bars (||)

($F > 1 && $F < 10) || ($F > 20 && $F < 30)

[Skybar]

Thank you!

Also, what is the difference between & and &&? Is it preferred to use &&?

[graham]

A singular & isn't a valid operator, you need to use 2 of them.

http://www.sidefx.com/docs/houdini12.5/expressions/_operators

[Skybar]

Oh I see, I actually thought it worked for me using only one before, but now when I try it doesn't.. Just my mind fooling myself I guess, my bad.

Thank you again, Graham!

[WesleyE]

An exmplenation about why it 'may' have worked before:

The singular AND (&) is a bitwise operator rather than an logical operator. The bitwise AND operation will compare the two and return every bit that are set in both variables, so for example:

if: 

a = 0011001
b = 1010001
c = a & b
1011001 = c
[/CODE]

The logical AND (&&) operator chains two comparrisons together.