Incrementing a number in a loop in plpgsql

I couldn't find this immediately from the examples. I want to increment a variable in a loop, in a function.

For instance:

DECLARE
   iterator float4;
BEGIN
   iterator = 1;

    while iterator < 999
       .....
      iterator ++;
END;

How would this be done?

I was looking at this document about flow control:
http://www.postgresql.org/docs/8.4/static/plpgsql-control-structures.html

And none of them seem to be relevant for me, unless these are absolutely the only ways to simulate incrementing a variable.