Q: My program's prompts and intermediate output don't always show up on the screen, especially when I pipe the output through another program.
A: It's best to use an explicit fflush(stdout) whenever output should definitely be visible (and especially if the text does not end with \n). [footnote] Several mechanisms attempt to perform the fflush for you, at the ``right time,'' but they tend to apply only when stdout is an interactive terminal. (See also question 12.24.)
References:
ISO Sec. 7.9.5.2
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