How to get -123 instead of 123?

Setup, Configuration and Use Beginners
1

Hi,
i get an item with a number in it. But this number is positive, i want to have it negative.

How can i do this?

I have a rule file, which extracts the value from a string.

val solarpowerStr = solar_lines.get(4).split('#').get(1)
stromzaehler1_leistung.postUpdate(solarpowerStr)

I tested the following, but with no luck, i got many errors:

Test 1:
val solarpowerStr1 = solarpowerStr * -1
stromzaehler1_leistung1.postUpdate(solarpowerStr1)

Test 2:
stromzaehler1_leistung1.postUpdate(solarpowerStr * -1)

Can someone help me?

2

stromzaehler1_leistung1.postUpdate( “-” + solarpowerStr )

1 Like
3

That works, thank you!

Why is my rule not working? How can i do some math? Is this not the right notation, if i want to calculate a value?

4

Your variable starts out as string, can’t do maths on that. You’d need to type cast it as a number to work with it.

My suggestion was to add a string “-” to the front of yours - the result is still a string, but if your stromzaehler1_leistung1 is a Number Item, the postUpdate will do an automatic conversion)

5

Can you tell me how I can change the string to a number within the rule so that I can do math with it?

6
7

This works:

var hausverbrauch_aktuell = (Double::parseDouble(consumptionStr)) + (Double::parseDouble(solarpowerStr))

But i have another question:

When i declare my variable in my rule before the first “if”

for example:

var Number Test

Can i store a string in it and it will automatically be parsed to a number like i do with the following code? And what´s the difference between var and val?

item.postUpdate(Test)

Also i got some errors inside my rule. When i store a value to a variable inside a “if”, then i can´t use it after the “if”.

How can i use the variable after the “if”?

Example:

rule "example"
     when xxx
     then
     val Test = 0
     if xxx {
          val Test = 1
          item_1.postUpdate(Test)
     }
     item_2.postUpdate(Test)
end

Now i get item_1 = 1 and item_2 = 0.

What do i have to do, so that i can change a variable inside an “if” and use the variable with the new value outside the “if” too?

8

This might help

If you want to change Test, use var not val. Unless you want to create a new version of Test, don’t use var or val again. If you want Test to be consistent both inside and outside a {} block, use var or val to declare it outside the block.

9

Thank you for the link. So i think i always can use var, because the variables are changed through the rule and not set before.

If i declare:

var number Test

And after that i put a string in it, will this be parsed to a number or will the variable change to a string? When i put a string to a number-item, it will get parsed to a number, but what about variables???

And if i declare a variable once at the beginning of a rule, i can use the name of the variable later without “var” before the name?

Like this:

var test = 1
test = 2 + 5
test = 3 + 5

And not this way:

var test = 1
var test = 2 + 5
var test = 3 + 5
10

It’s very easy to try these things out