[jagged-chisel]

We're not talking about scope. The scope is already decided. "Vars at the top of the block" doesn't mean "take those extra vars out of the while{} scope and elevate them to the next enclosing scope."

You've taken my "scratch space" too literally. Very few people need to count bytes for local vars. I'm talking about future maintainers reading and understanding code. Grouping the current block's variables at the top says nothing about how the compiler might organize the resulting code and storage. But it does inform future readers of the code.

[nybble41]

The scope of a variable is from where it is declared to the end of the block. Moving a variable to the top of the enclosing block means that it can be referenced from more places in the code, which increases its scope.

Warnings about uninitialized variables help, but don't catch everything. For example, you don't usually get a warning for passing the address of an uninitialized variable to an external function (since it might be an output parameter), but that would be undefined behavior if the function expects the variable to be initialized. Initializing variables at the point where they are declared ensures that they can't be referenced at all in an uninitialized state.

Rust has a slightly more nuanced (and IMHO superior) system: non-mutable ("const") variables can be assigned exactly once, possibly but not necessarily at the point where they are declared, and all variables must be initialized before use, including passing references to other functions. This permits more flexibility in how the code is arranged while simultaneously offering stronger guarantees against undefined or otherwise erroneous behavior.