Comment by 20k

You use the status of NDEBUG to control whether or not your asserts are run. I don't understand how this is complex

If you want to use asserts, you need to control the definition of NDEBUG. You either do this with your build system (common), or manually (slightly less common). This is literally <assert.h> 101

The preprocessor is widely used for a variety of things when its necessary, including #includes and #defines, because there's literally no other mechanism for this. Its bizarre to say that nobody controls the definition status of NDEBUG because people don't use the preprocessor