Fix warning about `printf`:

[Jarod42]

• warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type std::size_t.

[Eric-01]

Why not %zu instead? :)

[Jarod42]

Not familiar enough with printf format. I know that std::size_t might be of different size, warning suggests %ld as fix, so wrong for other size. Not sure neither if %zu is supported by all compiler...

[AJenbo]

Testing via GodBolt it seems it should be supported on: Clang 5, GCC 5, djgpp 5.5, icc 16, icx 2021, MSVC 19, nvc++ 22, FRC, TI CL430, Zapcc

It appears that it's more common for compilers to not support C++17 then %zu.