asp.net - DataGrid summing values incorrectly -

i summing value of column in datagrid updated every time datagrid updated. say, user selects value in datagrid1 adds data datagrid. part working wonderfully. need sum 1 of columns gives me total. code came with, fires under gridview1.selectedindexchanged event.

        each gridviewrow in gridview2.rows               sum = convert.todouble(row.cells(3).text)             total = sum + total             lbltotal.text = total.tostring          next 

now problem comes this. if have rwo values, of say... 2.00, sum ok. it'll give me 4. if add item, item2, has value of 2.30 gives me total of 4.60. if first add 2.30 item , add 2 item gives me value of 4. heck going on , how can such simple math go wrong :p! missing something? rounding? need parse something?

full code ahead

 protected sub gridview1_selectedindexchanged(sender object, e eventargs) handles gridview1.selectedindexchanged       dim row = gridview1.selectedrow     if not row nothing andalso isnumeric(row.cells(3).text)         dim price double = cdbl(row.cells(3).text)         dim name string = cstr(row.cells(2).text)         lblcart.visible = true         dim infototal string = "$" & "    " & precio & "      " & nombre           dim total double          if gridview2.rows.count = 0             '  dt = new datatable()             dt.columns.add(new datacolumn("name", gettype(system.string)))             dt.columns.add(new datacolumn("price", gettype(system.string)))         else             dt = directcast(session("datatable"), datatable)         end if          dim sum double         dim dr1 datarow = dt.newrow()         dr1(0) = name.tostring         dr1(1) = cdbl(price.tostring)         dt.rows.add(dr1)         gridview2.datasource = dt         gridview2.databind()         session("datatable") = dt          each gridviewrow in gridview2.rows             sum = cdbl(row.cells(3).text)             total += sum         next          lbltotal.text = total.tostring         listbox1.items.add(cstr(infototal))      end if   end sub 

it sounds missing additional code in there adding value twice - please post full code. below accomplishes doing (ever slightly) less code - also, no point updating label until for has finished.

for each gridviewrow in gridview2.rows                 sum = cdbl(row.cells(3).text)                 total += sum             next  lbltotal.text = total.tostring