Issue on function in plsql

I have the below function I am trying to write but when I execute plsql with debugger it says the below error

at line

Begin

         SELECT TO_CHAR(ordered_date,'MON')

          into odate

          FROM oe_order_headers_all

          where header_id =p_header_id

execution has terminated at line

'  Begin

      if avg_ord_qty > fmon then  ....'

Could anyone help to solve the issue

I need to compare the average sales of the last 3 month with the forecast.  Which ever highest shld be compared with (onhand qty+pending qty-requested qty of actual order) COMAPRED QTY

If average sales or forecast < Compared qty it should return 1 else it return 0