include/opt: Improve code readability

include/opt: Improve code readability

There are several functions in the opt module where local variables
are not declared in the most narrow block possible, statements are
needlessly spread over multiple lines, and values used only once
are assigned to variables; all of which impeding readability.

This commit modifies the opt module to remove cases of assign-once-
read-once variables, remove integer increments on separate lines,
make the "scope" of variables narrower, and declare variables
with a type, where possible.