You have a created a perfect example of why namespaces can be useful. In particular you have a name clash with the function SortArray() becuase you have declared and defined a function called SortArray in intSort.h and intSort.cpp in addition to a function called SortArray outside of intSort.h but both are in your program. Therefore, the linker isn't sure which version of SortArray to use so it is calling it an unresolved external error. I suspect if you comment out the prototype for SortArray you have typed just above the declaration of the global constants, that this error will resolve.
BTW, your indentation is much better with this last post, congrats. However, it should be int main() not void main() and, if your compiler supports it, you should really consider using the updated versions of iostream, etc. and handle the namespace issue associated therewith in a manner you are comfortable with.
