Hello.

Suppose you're collecting data in an array called buffer and it contains "mississippi".
To find at which positions within the array there is an "i" you can use another array, e.g. search_result, and store those positions in it.

Something like this:

Code:
search_item="i"
cnt=0
for n=0 to 10
if buffer[n]=search_item then search_result[cnt]=n
cnt=cnt+1
next n

If you'd look, say, for an "s" then you could replace
search_item="i"
with
search_item="s"