The problem with C0 (it's "C-naught", not "C-not") is that it is a toy language used for the compilers class which has somehow made it down into the intro curriculum. It is not useful in the real world; absolutely no one outside of CMU uses it. It is useful only as a stepping stone for C -- at which point, why not just teach C, and keep to a "safer" subset for a while? A couple weeks "transition" to get used to malloc and gdb and NULL pointers and segmentation faults etc is not nearly enough.