Scan a string from a specified starting position for the 
   end of a number.  

   None. 

   VARIABLE  I/O  DESCRIPTION 
   --------  ---  -------------------------------------------------- 
   string     I   Any character string.
   first      I   First character to scan from in string.
   last       O   Last character that is part of a number.
   nchar      O   Number of characters in the number. 

   string      is any character string. 

   first       is the location in the string to beginning scanning 
               for a number.  It is assumed that the 
               number begins at first.  

               The normal range of first is 0 : strlen(string)-1.

   last        is the last character at or after first such that the
               substring ranging from string[first] through
               string[last] is a number.  If there is no such
               substring, last will be returned with the value first-1.

               If a number is found, last will be in the
               range is 0 : strlen(string)-1.


   nchar       is the number of characters in the number that
               begins at index first and ends at last.  If there is no
               such string nchar will be given the value 0.

   None. 

   This routine allows you to scan forward in a string to locate a
   number that begins on the input character first.   Note that all
   decimal numbers are included in the list of numbers. The main
   difference between decimal numbers and numbers is that numbers may
   have an exponential expression attached (i.e. the exponent character
   'e','E','d' or 'D' followed by an signed integer).

   1) Suppose you believe that a string has the form 

         X%Y%Z 

      where X, Y, and Z are numbers of some unknown length and
      % stands for any character that cannot occur in a number.
      You could use this routine to locate the numbers in the
      string as shown below.  We'll keep track of the beginning and
      ending of the numbers in the integer arrays b and e.


         #include <string.h>
         #include "SpiceUsr.h"

               .
               .
               .

         first = 0;
         i     = 0;
         len   = strlen(string);

         while ( first < len-1 )
         {
            lx4num_c ( string, first, &last, &nchar );

            if ( nchar > 0 )
            {
               i++;

               b[i]  = first;
               e[i]  = last;
               first = last  +  2;
            }
            else
            {
               first++;  
            }
         }

   None. 

   1) If first is beyond either end of the string, then 
      last will be returned with the value first-1 and nchar 
      will be returned with the value 0. 

   2) If string[first] is not part of a number then last 
      will be returned with the value first-1 and nchar will be 
      returned with the value 0. 

   3) If the input string pointer is null, the error SPICE(NULLPOINTER)
      will be signaled.

   4) If the input string has length zero, last will be set to first-1
      and nchar will be set to zero.  This case is not considered an
      error.

   None. 

   N.J. Bachman    (JPL)
   W.L. Taber      (JPL) 

   None. 

   -CSPICE Version 1.0.0, 18-AUG-2002 (NJB) (WLT)

   Scan a string for a number.