compiler question

Hello,

I recently started working with XCode. I was curious why programs compiled under xcode do not run when used in a unix environment. For example, when I wrote the Hello World program in Xcode and moved it to my linux machine it would not run. I had to gcc main.c before it would run. I thought the underlying architecture for OS X was unix so I expected ./HelloWorld to run.

Thank you for your help!

Unix does not equal Linux. Mac OS X is Unix, Linux is Unix-like. You'll find that despite similiarities, you'll have to recompile programs. Someone with more experience in deploying across OSes can be more clear on that one.

Is your linux machine a PC? If yes that's your main problem right there.
Even if not, like Van said not all *nixes are equal. Also some libraries are machine specific and need to be recompiled for that machine.