32bit & 64bit programming

If u make a program that can run on a 32-bit OS, in most case, all u
have to do is rebuild it for 64-bit environment.

u can compile a 64-bit program on 32-bit environment. All u have to do
is get the compiler and Libraries for 64-bit program.

Some of the 32-bit programs cannot run corrently on 64-bit OS, so u
have to rebuild(recomile) it for running on 64-bit OS.

Good luck, anyway.