"Larry Lard" wrote:

>
> Ben R. wrote:
> > In an article I was reading
> >
> (http://www.ftponline.com/vsm/2005_06/magazine/columns/desktopdeveloper/),
> >
> > I read the following:
> >
> > "The ending condition of a VB.NET for loop is evaluated only once,
> while the
> > C# for loop ending condition is evaluated on every iteration."
> >
> > Is this accurate? I don't understand how you could get away without
> > evaluating the ending condition at every iteration. Otherwise, how
> would you
> > know whether or not to exit?
>
> This is arguably accurate, but misleading. (What follows assumes
> knowledge of C#)
>
> The correct VB.NET construction to compare a C# for loop to is not a
> For ... Next loop. Let us review a C# for loop:
>
> for ( <initial statement> ; <loop continuation condition> ; <step
> statement> )
>    <statment block>
>
> [no nitpicks please :)]
>
> Note that the initial statement and step statement can be ANY statement
> you like. What this is equivalent to is a particular form of the VB.NET
> Do ... Loop loop:
>
> <initial statement>
> Do While <loop continuation condition>
>    <statment block>
>
>    <step statement>
> Loop
>
> Whereas a VB.NET For ... Next loop:
>
> For <index> = <start value> To <end value> Step <step value>
>    <statement block>
> Next
>
> is equivalent to this, *different*, Do ... Loop loop:
>
> <index = start value>
> <CONST end value = whatever>
> Do While <index <= end value>
>     <statement block>
>
>     <index += step value>
> Loop
>
> That CONST is effectively what the referenced article is talking about:
> With a VB.NET For ... Next loop, the end value is evaluated ONCE, and
> for the whole time the loop is looping, the loop continuation condition
> is 'index <= end value'. With a C# for() loop, the actual *expression*
> supplied as the loop continuation condition is evaluated EVERY TIME
> around.
>
> Example:
>
> VB.NET:
>
> Dim endvalue as integer = 10
> dim i as integer
>
> for i = 1 to endvalue
>     msgbox(i.tostring)
>     endvalue \= 2
> next
>
> 'Because endvalue is evaluated ONCE at the start of the loop,
> 'you will see TEN messageboxes
>
> C#:
>
> int ev=10;
> int i;
>
> for(i=1; i<=ev; i++)
> {
>     MessageBox.Show (i.ToString());
>     ev /=2;
> }
>
> // because "i<=ev" is evaluated EVERY TIME ROUND,
> // you will see only TWO message boxes
>
> Make sense?
>
> --
> Larry Lard
> Replies to group please
>
>