Android Tutorial For vs. While

While usually interchangeable, we should all be aware of one very important difference between these two cycles.
The For...Next cycle caches the "goal", the Do...Loop does not.

Happy coding!

 

[thedesolatesoul]

I dont know if that is a B4A or Java compiler optimization, but did you try returning a different value from the function? (For e.g. return a random number?)
In a for loop, the termination condition has to be evaluated on every iteration, i.e. is i < OneHundredThousand(i), but since the function returns a static value it is possible the compiler optimized it.

 

[wonder]

There's no difference returning a random number.

Please note that, I'm not pointing this situation as a bug, but rather as a feature of the language.

 

[thedesolatesoul]

I know.
Just to clarify this 'feature' is inherent to B4X, this is not a Java feature.
During translation from (for e.g.) B4J to Java, the bounds are cached.
Personally, I think this is an incorrect design decision. The decision to cache the bounds should be left to the developer, not the language.

Imagine:

Sub AppStart (Args() As String)
    Dim i = 1 As Int
    For i = 1 To OneHundredThousand(i)
    Next
    Log("for loop completed " & i)
End Sub

Sub OneHundredThousand(i As Int) As Int
    Dim s As Char
    If i > 1 Then s = "s"
    Log("This function was called " & i & " time" & s)
    Return i+5
End Sub

 

[MaFu]

For the most languages the upper bound is evaluated only on loop start, this is the normal behaviour of the for loop. If a bounds recalculation is needed then a while should be used.

 

[thedesolatesoul]

For the most languages the upper bound is evaluated only on loop start, this is the normal behaviour of the for loop. If a bounds recalculation is needed then a while should be used.

Can you add some more substance to your post?
Why is it normal behaviour?

 

[MaFu]

Maybe it was a hasty conclusion. I name it "normal" only in relation to "most languages". But also many languages use the other way and evaluate on every loop cycle.

You think it's an incorrect design decision because java evaluates on each cycle. But B4X is Basic and in Basic the evaluation is only done at loop start. Therefore it is correct implemented.
Only my opinion.

 

[thedesolatesoul]

Maybe it was a hasty conclusion. I name it "normal" only in relation to "most languages". But also many languages use the other way and evaluate on every loop cycle.

You think it's an incorrect design decision because java evaluates on each cycle. But B4X is Basic and in Basic the evaluation is only done at loop start. Therefore it is correct implemented.
Only my opinion.

The way you wrote it sounded like a fact, which is why I questioned you. I think the keyword in your post is 'opinion'.
I'm still disappointed you didnt name many languages, atleast I would have learnt something. Do you have some source or link, atleast I'd like to see which 'Basic' you are talking about?

 

[Erel]

VB .Net and VB6 also evaluate the limits before the first iteration: https://msdn.microsoft.com/en-us/library/5z06z1kb.aspx