[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.