for i: Integer := 0 to 10 do
for i: Integer := 0 to 20 do
Console.Writeline(i)

The Prism feature with the for loop variables:

var x := -1;
var list := new List([1, 2, 3]);

1
2
3
-1

At the end, x will still be -1, because it is a different variable than the x inside the loop.

”
(Taken from the prism wiki)

Is this good readable code? I don’t think so. You’ll use the “x” variable but inside the “for” loop it’s a different “x” – same name, different behavior/content? The only thing I see is to use special variables only intended for use within for loops (like I,J,K,L) – which we do anyway.

Or why not using special prefixes (like in PHP, Perl, etc.) for those cases?

for $x in list do
Console.Writeline(x)
?

But if you need some variables for loops (like the allmighty ‘for i := 0 to…’), or only in scope of a loop, then it’s a lot cleaner to not declare it oustide of that scope.

Being able to access a variable that was valid in a loop and might or might not be available for access later is generally a bad idea. Declaring a variable that is used only in a loop directly in that loop makes the code cleaner and more maintainable.