Rookie problem with variables

BlitzPlus Forums/BlitzPlus Programming/Rookie problem with variables

koekebakker

(Posted 2004) [#1]

Since the help of B+ is pretty worse I can't find
a solution to this problem.
How can i exchange a variablele to the main loop of my
program and a function

Function test(a,b)

Print b
a=52

End Function

; main loop

b=44
test(a,b)
Print a

While Not KeyHit(1)
Wend

End

----------------------------------
it returns

44
0

I don't get it.

Warren

(Posted 2004) [#2]

Because variables are local to the function they are in. If you pass a variable into a function, you aren't modifying the original - you're modifying the copy that was made for the function when it was called. Types are an exception to this rule, but that's another show...

To do what you want, either declare "a" and "b" as global vars at the top of your program, or return "a" from the function and capture that return value in your main loop.

koekebakker

(Posted 2004) [#3]

Actully WarrenM a and b must be both variable so they cant'
be globals

How can I return a variable out of a function into the main loop?
I cannot make a global of it inside a function.
Why?!?!? Is it that hard to program such "feature" in B+ ?
I can't see the bennefits of locking a variable in a function

Anyway. see my goal below.

When i click my mouse the function checkmousepos() is called

In the function checkmousepos() is a calculation going on
that returns the values tileborderx and tilebordery to the
main loop. IN the mainloop the values tileborderx and
tilebordery are used to draw a rectangle.

Any clear advice?
You was talking about capturing. Can you give me an example
of that?

Thank you

Warren

(Posted 2004) [#4]

Capturing:

a = test(a,b)

Then change "test" to read:

Function test(a,b)

Print b
a=52

return a

End Function

Variable scoping is a very common (and necessary) thing in programming languages. If this is your first attempt at coding something, I understand your confusion. But in time you'll see that the reasons for it are very sound.

If you want to be able to access a variable from anywhere in your program, declare it global at the top of your file.

global MyVar

Now, everyone can talk about MyVar and they'll be talking about the same variable.

Blitz has the added confusion inherent to most BASIC dialects ... if you use a variable name that it hasn't seen in the current scope, it creates it for you automatically. This leads to all sort of fun programming errors related to scope confusion and name mismatches.

But if you want to use BASIC, that's the trade off you have to accept.

koekebakker

(Posted 2004) [#5]

Great... but is it possible to return more then one
varaibele out of a function since after a return the
remaning content of the function will be ignored?

I'll stop nagging after that :)

Warren

(Posted 2004) [#6]

No, you can't return multiple variables unless you wrap them in a Type. And if you're going to do that, just pass in the Type to the function since you ARE modifying the actual variable when it comes to Types.

koekebakker

(Posted 2004) [#7]

That is no problem. I have the tick to do as much as
possible in functions now I own Visual Blitz. With the
expand/collapse option) my code looks very clean.
But I found out that a good organized mainloop is just as
effective and more flexible.