I want to upload a file into an document library having flag value. When we do upload a file flag value should be "Zero" and when we click save flag value should be updated as "one" using object model

you can use the sandbox feature bind to a documents library. pay more attention to the event "ItemUpdated". the event will be fired twice. the first time when uploaded, and the second time when saved.

public override void ItemUpdated(SPItemEventProperties properties)
{

}