This function prompts a user for keyboard input.

   None.

   Variable  I/O  Description
   --------  ---  --------------------------------------------------
   prmptStr   I   The prompt string to display when asking for input.
   lenout     I   Minimum number of characters for response plus one.
   buffer     O   The string containing the response typed by a user.

   The routine also returns a pointer to the output buffer.

   prmptStr   A character string displayed from the current cursor
              position which describes the requested input.  The prompt
              string should be relatively short, i.e., 50 or fewer
              characters, so a response may be typed on the line where
              the prompt appears.

              All characters (including trailing blanks) in prmptStr
              are considered significant and will be displayed.

   lenout     The integer number of characters plus one for the
              response string.

   buffer     The user supplied string which holds the response.  The
              string's memory is allocated in the calling routine.

   The routine returns a pointer to buffer as well as passing the
   pointer back via an argument.

   None.

   This is a utility that allows you to "easily" request information
   from a program user.  The calling program declares an array or
   allocate memory to contain the user's response to the prompt.

   Suppose you have an interactive program that computes state
   vectors by calling spkezr_c.  The program prompts the user for
   the inputs to spkezr_c.  After each prompt is written, the program
   leaves the cursor at the end of the string as shown here:

      Enter UTC epoch  > _

   (The underscore indicates the cursor position).

   The following program illustrates the aquisition of input
   values using prompt_c:

   #include <stdlib.h>
   #include <stdio.h>

   #include "SpiceUsr.h"

   #define   STRLEN    32

   void main()
      {
      SpiceChar    utc    [STRLEN];
      SpiceChar    obs    [STRLEN];
      SpiceChar    targ   [STRLEN];
      SpiceChar  * utc1;
      SpiceChar  * obs1;
      SpiceChar  * targ1;


      /. Call the routine as a subroutine. ./

      prompt_c ( "Enter UTC epoch             > ", STRLEN, utc  );
      prompt_c ( "Enter observer name         > ", STRLEN, obs  );
      prompt_c ( "Enter target name           > ", STRLEN, targ );


      /. Or call the routine as a function. ./

      utc1   = ( SpiceChar * ) malloc (STRLEN);
      obs1   = ( SpiceChar * ) malloc (STRLEN);
      targ1  = ( SpiceChar * ) malloc (STRLEN);


      utc1 = prompt_c ( "Enter UTC epoch        > ", STRLEN, utc1 );
      obs1 = prompt_c ( "Enter observer name    > ", STRLEN, obs1 );
      targ1= prompt_c ( "Enter target name      > ", STRLEN, targ1);


      /.
      Now do stuff with your strings.
      ./

        ...

      }

   None.

   1) If the output string has length less than two characters, it
      is too short to contain one character of output data plus a null
      terminator, so it cannot be passed to the underlying Fortran
      routine.  In this event, the the error SPICE(STRINGTOOSHORT) is
      signaled and a null pointer is returned.

   None.

   N.J. Bachman    (JPL)
   K.R. Gehringer  (JPL)
   W.L. Taber      (JPL)
   E.D. Wright     (JPL)

   None.

   -CSPICE Version 1.0.0, 25-JUN-1999 (EDW) (NJB)

   Prompt for keyboard input
   Prompt for input with a user supplied message