Your code won't work in this case :)

Bigstring = 'cattttccvtttt'


>The simplest way would be to loop through the big string and check if the current character is already in the result. If not, add it.
>

lpara tcBig
>c=""
>for i=1 to len(tcBig)
>   ch=subs(tcbig, i, 1)
>   if not ch$c
>      c=c+ch
>  endif
>endfor
>return c

update: wow mine code either... :)

my code just a bad copy of yours. I'm another Code Hood... :)