Okay, so you write your own string library. Now you'd like to do the same thing for resizable arrays, so you write a resizable array li… oops, you can't, because C doesn't have parametric types.
He didn't say "write your own library". He said "use" one (your own if you prefer). Or are you going to suggest there are no good string handling libraries for C?
It doesn't matter. My point is that it's not possible, not for you and not for anyone else, to implement a type-safe generic resizable array library in C.