Common Compiler Errors for CS 2040 (with fixes)

These are currently unorganized, but the error messages are in bold text.

• The compiler complaints that a particular class is an incomplete type:
  This means you have declared a class but not defined it in the implementation. For example,

          class X;
          class Y { X *stuff; ... };
  

  and then writing

          stuff->do_something();
  

  in a .cpp file. The fix is to include the file that defines X:

          #include "x.h"
          ...
          stuff->do_something();
  

  Without that include directive, the compiler cannot determine if do_something() is a legal operation.