[.net] [C#]Simple variable scope problem

When you put int i; outside the for loop, whether it is above or below it it is still declared in the scope outside the for which causes problems with the i nested within the scope of the for loop.

The solution would be to use:

int i;for (i = 0; i < steps; i++) { // Note removal of 'int'    // use i}// use i

Coming from Java I found this behavior quite puzzling too at first, but apparently it's by design as per section 8.5.1 of the C# language spec. According to the specifcation, the variable i exists in the entire enclosing scope in which it is defined, including child scopes.

Effectively this means that...

void SomeFunction(){  int i = 0;  for(int i = 0; i < 1; i++) {}}

...and...

void SomeFunction(){  for(int i = 0; i < 1; i++) {}  int i = 0;}

...are kinda equivalent in that they are illegal/incorrect redefinitions of the same variable. That the former case is incorrect should not be surprising, since you can't redeclare int i in the for loop. The C# spec however dictates that int i the latter snippet exists in the entire scope of SomeFunction(), so it's pretty much incorrect for the same reason as the first snippet is.

This decission was made to prevent unintended re-use of existing variables, as described here on MSDN. For some speculation, I'd guess that this decission also might make optimization easier on the C# compiler, since variables in a scope and its child scopes will be uniquely named, so the compiler can move around local scoped instructions and local child scopes as it sees fit.

gonzo - I believe this is a choice they made on purpose to disallow bad programming habits,
in this case using same name to different variables in the same function. Even if possible for the compiler to understand what you mean, it is a bad habit as it makes code less readable to humans and/or may cause hard to find bugs.

Thank you for solution and explanation!

I tried removing int from the for loop before, but it didn't work. I took a closer look at the code and I had another for loop hidden in a #region. Now it works correctly and I've learnt something new [smile]