Pop Quiz what is wrong with this code?

[Kagamin]

On Monday, 22 June 2020 at 13:24:32 UTC, Steven Schveighoffer 
wrote:
> But the OP rejected the idea of using ptrdiff_t (or did he?), 
> which would solve that problem.
>
> It's really hard to tell what the problem is without more 
> definition or explanation.

OP is precise:

On Saturday, 20 June 2020 at 16:00:40 UTC, Danni Coy wrote:
> more specifically I didn't want them to be unsigned

The discussion was just derailed.