Ada String Issue: String within Strings

[amuhtar@uoguelph.ca (Xcalibre)]

Just a little hello and little comment that I've enjoyed reading
through this newsgroup.

My problem is this:  I am Get_Line-ing from a file... what I want to
do is check that line of text for a particular phrase given (not just
a word).  I've tried using Index() and I get an Error that says...

extract.adb:73:66: array type required in indexed component

The code reads:
   Get_Line (f_From, LineItem, Index);
   while (not End_Of_File(f_From)) loop
      Found := 0;
      Found := Index (LineItem(1..Index), Catch);
      if Found > 0 then
	Put_Line(f_To, LineItem(1..Index));
      end if;
   end loop;	

where
LineItem, Catch : String(1..1024);
Found : Natural;

Is what I am doing the right idea or is there a different built in
function that will do what C does in comparing the text and returning
the location of where it starts?

Thanks in advance
Andrew