[mhartl]

The code

    printf("goodbye, Dennis");

would give

    $ ./goodbye
    goodbye, Dennis$ 

What you want is to add a newline ('\n') at the end:

    printf("goodbye, Dennis\n");

Now you get

    $ ./goodbye
    goodbye, Dennis
    $

That's why the canonical "hello, world" program contains the line

    printf("hello, world\n");