I'm not sure if I catch your meaning here... You can make a regular unix program (one using stdin, stdout, and stderr for example) by choosing "C++ Tool" from the new project options.
If you mean you want to be able to do stdin and stdout on your Cocoa gui programs, the debug console does read from the keyboard. Just set a breakpoint, do a debug run, and type away. The debugger seems to do a really poor job with Obj-C, but I assume they just haven't gotten around to working on that yet.