Function            strcomma - convert a string to xx,xxx,xxx format

  Syntax              char *strcomma(char *source);

  Prototype in        stringhk.h

  Remarks             strcomma converts a string of numbers into the
                      comma delimited format (xx,xxx,xxx). The number is
                      terminated by a non-digit (any character other than
                      0-9.) A leading sign will be copied before
                      converting the number.

  Return value        returns a pointer to the storage location
                      containing the comma formatted string, or NULL if
                      space could not be allocated. The returned string
                      is NOT the same as the string passed to the
                      function. This function does NOT write over the
                      string passed to it.

  See also            strtocomma()

  Example             #include <stringhk.h>
                      #include <stdio.h>            /* for the printf */

                      main()
                      {
                           char sint[15], *comma;

                           strcpy(sint,"12839.44");
                           comma = strcomma(sint);
                           printf("%s -> %s\n",sint,comma);
                      }

  Program output      12839.44 -> 12,839.44