[matthavener]

Why?

[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");

[Lukeas14]

"\n" is a linebreak which would guarantee the text is printed and place whatever output came afterwards on the next line.

[derefr]

Isn't the output stream at least guaranteed to be flushed once on completion of the program, though?

[djcapelis]

Yes, it flushes completely outputting all characters. None of which contain a newline.

Flushing doesn't automatically add newlines for you in C. It flushes the buffers you gave it, it doesn't make new stuff up to print out along with your buffers.

[derefr]

(Right, I didn't mean to suggest it added a newline; just that adding a newline flushes the buffer, which was one half of the problem with missing a newline—but that if this is the only line of the program, this half of the problem is obviated.)

[getsat]

Adding a newline doesn't flush anything. You'd want to call fflush() to do that.

[bremac]

printf prints to standard output, which is line-buffered by default when reading from a tty on UNIX variants. This can lead to strange problems for those who try to use it to track which parts of a program are being executed, as demonstrated by the following program with an infinite loop:

  #include <stdio.h>
  int main(int c, char **v) {
    printf("Hello\nJello");
    while(1) ;
    return 0;
  }