Using Looping Cursors Update a Table

Create proc proc_UpdateGenSerial
As
Begin
	declare cur_GenSerial cursor 
	For select itemcode,icode from tbl_TableName
	Declare @itemcode int,@icode int,@oldicode  int,@newserialnum int
	set @newserialnum = 1
	open cur_GenSerial 
		fetch next from cur_GenSerial into  @itemcode,@icode
		while(@@FETCH_STATUS=0)
		Begin
			if @itemcode = 1
				Begin
					set	@oldicode = @icode
				End
			
			if(@oldicode = @icode)
				Begin
					Update	tbl_GenSerialNum
					Set		serialnum = @newserialnum
					Where	itemcode = @itemcode
					
					set @newserialnum = @newserialnum + 1
				End
			Else
				Begin
					set @newserialnum = 1
					
					Update	tbl_GenSerialNum
					Set		serialnum = @newserialnum
					Where	itemcode = @itemcode
					
					set @newserialnum = @newserialnum + 1
					set	@oldicode = @icode
				End
		fetch next from cur_GenSerial into  @itemcode,@icode
		End
	Close cur_GenSerial 
	Deallocate cur_GenSerial 
End