CEikFloatingPointEditor控件的问题

我写的最简单的+,-计算器，导航键向上加向下减，但是不知道哪里的问题，运行时只能写数字，却不能运算，不知为何？请大家帮助一下
TKeyResponse CHelloworldContainer::OfferKeyEventL( 
const TKeyEvent& aKeyEvent, 
TEventCode aType )
{

   if ( aType != EEventKey ) // Is not key event?
        {
        return EKeyWasNotConsumed;
        }
   TReal dt;
   CAknNumericEdwin::TValidationStatus ageStatus;

    switch ( aKeyEvent.iCode )
        {
        case EKeyDownArrow: 
          aOpe ='-';
         ageStatus =iFloatingPointEditor1->GetValueAsReal(dt);
         if(ageStatus==CAknNumericEdwin::EValueValid)aElem1=dt;
         return EKeyWasConsumed;
         break;
        
        case EKeyUpArrow:
         aOpe ='+';
        
         ageStatus =iFloatingPointEditor1->GetValueAsReal(dt);
         if(ageStatus==CAknNumericEdwin::EValueValid)aElem1=dt;
         return EKeyWasConsumed;
            break;
        case   EKeyEnter:
         ageStatus =iFloatingPointEditor1->GetValueAsReal(dt);
         if(ageStatus==CAknNumericEdwin::EValueValid)
         {
         aElem2=dt;
         TReal res;
         if (aOpe=='-')
         res = aElem1-aElem2;
         else if (aOpe=='+')
         res = aElem1+aElem2;
         iFloatingPointEditor1->SetValueL(&res);
         }

         return EKeyWasConsumed;
         break;
        
        default:
        if(iFloatingPointEditor1)
     {
     return iFloatingPointEditor1->OfferKeyEventL(aKeyEvent, aType );
     }
         else
                {
                return EKeyWasNotConsumed;
                }
        }
    return EKeyWasConsumed;
}

补充：移动开发 ,  Symbian