The Free On-line Dictionary of Computing (30 December 2018):

printf

    The standard function in the C programming
   language library for printing formatted output.

   The first argument is a format string which may contain
   ordinary characters which are just printed and "conversion
   specifications" - sequences beginning with '%' such as %6d
   which describe how the other arguments should be printed, in
   this case as a six-character decimal integer padded on the
   right with spaces.

   Possible conversion specifications are d, i or u (decimal
   integer), o (octal), x, X or p (hexadecimal), f
   (floating-point), e or E (mantissa and exponent,
   e.g. 1.23E-22), g or G (f or e format as appropriate to the
   value printed), c (a single character), s (a string), %
   (i.e. %% - print a % character).  d, i, f, e, g are signed,
   the rest are unsigned.

   The variant fprintf prints to a given output stream and
   sprintf stores what would be printed in a string variable.

   Unix manual page: printf(3).

   (1996-12-08)