Library /sys$common/syshlp/dbg$help.hlb DEBUG, Built in Symbols, %PARCNT  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Specifies the number of actual parameters to the current command
    procedure. Use %PARCNT in command procedures that can take a
    variable number of actual parameters. You can use %PARCNT only
    inside command procedures; it is not defined when commands are
    entered from the terminal.

    For example, suppose the command procedure ABC is executed with
    the command @ABC 111,222,333. Inside ABC, %PARCNT then has the
    value 3 because there are three parameters on this particular
    call to ABC.

    Example:

    EVALUATE %PARCNT
    FOR I = 1 TO %PARCNT DO (DECLARE X:VALUE; EVALUATE X)