Replace CHAR with VARCHAR2

How can I replace CHAR with VARCHAR2 in all tables in a schema?

Note: I'm content with a query that returns the ALTER TABLE statements so I can save the script and run it again.

From stackoverflow

• select 'ALTER TABLE "' || owner || '"."' || table_name
  || '" MODIFY ("' || column_name
  || '" VARCHAR2(' || data_length || '));'
  from all_tab_columns
  where data_type = 'CHAR'
  and owner = :schemaname
  and exists (
      select 1
      from all_tables t
      where tc.owner = t.owner
      and tc.table_name = t.table_name
  );
  

  Aaron Digulla : I've extended the original answer to omit tables which are in the recycle bin. See http://stackoverflow.com/questions/2446053/what-are-the-bin-tables-in-oracles-all-tab-columns-table