ohh yeah I have noticed that you can calculate string and integer.. that is very strange, but I think they must somehow throw an error so that developer can be aware of calculating string and int. I think problem will start if you somehow retrieve data from database with different datatype and do calculations, somehow you wont see any error message about that then now you have to go throw the code trying to figure about why the output you get is not what you expected because you mistakely calculate string and int. So it needs more attention when you do calculations or build a huge application. anyway thanks for that.