how to truncate an array

[Ray Andrews <rayandrews@xxxxxxxxxxx>]

This should be dead simple, but I can't figure out how  to do it. I have 
an array that can be
arbitrarily long, and I want to truncate it at 20 elements.

    setopt POSIX_STRINGS
    string[20]='\0'
    echo "string is now truncated: $string"

... I've tried every variation on the above theme that I can think of 
with no luck.
I know that zsh likes to not truncate strings on 'null' but 
'POSIX_STRINGS' is supposta
force that, no? There must be a simple way to do this. I guess I still 
have C on the brain
but it seems to me that it is God's will that a null terminates a string ...
>