Variable outside or inside block??

[BlackStone]

Is it better to declare a variable outside of a loop, or does it not matter (performance wise)??

 

int start = 0;
int end = size - 1;            

while (start <= end)
{
   // Put it here or outside the block??
   int middle = (start + end) / 2;
   ....
}

[PlausiblyDamp]

Performance wise it should make very little difference, from a code point of view though if the variable is only used within the block then declaring it within the block makes the code's intention that bit clearer and allows the compiler to enforce the variable scope.

[Tygur]

I would say that any change in performance is negligable, if it's even there. The variable will still live until the procedure ends no matter where you declare it. It doesn't die once you leave the block, and it'll still have the same value if you reenter it.

[BlackStone]

I thought that space is made on the stack for the variable each time the block is entered. So, basically the variable just has scope in the block, but the variable is created once the procedure is called (Is that right)?

[Tygur]

I don't know when the variable is created. I suppose it's possible that it might not be created until the block is entered. That's kind of difficult to test. But the variable does live after you leave the block.

 

Here's Microsoft's documentation on the matter:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vbcn7/html/vaconvariablescope.asp