Large Memory Model Problems (DOS or XENIX)

• You are passing a 0 when you should be passing a NULLP or NULLFP. This causes problems with any memory model except the small memory model. In general, you should always use NULLP for null data pointers and NULLFP for null function pointers.
  
  
• You did not declare your functions that return pointers in the calling function. Also, if you use standard library functions that return pointers, you must declare these functions in the calling function or include the header files with the ANSI prototypes. If you do not declare functions, the C compiler assumes that the function returns an integer value, which in many cases is shorter than a pointer.