VMS Help CC, Run-time functions, gcvt  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Converts its value argument to a null-terminated string of ASCII
  digits and returns the address of the string.  The strings are
  stored in a memory location created by the function.

  Syntax:

       #include <stdlib.h>

       char *gcvt(double value, int ndigit, char *buf);