I am developing an application in which I need to find the apps which are already installed in iPhone device such as Skype, facebook. I need to check it. Please give me code
Tapbots does something similar but only with their own apps. They probably keep track of device UDIDs on a server of theirs by communicating with the server using each app, so they are able to show which of their apps are installed on a given device.
As mentioned, this only works for apps you make though, as you'll be the one programming such functionality into your apps. You cannot check the existence of apps made by others.
There are also no public APIs that allow you to disable other apps. And besides, as the others say, apps are all sandboxed to themselves.
By the way... if you're trying to disable those apps because they compete with yours... forget it. The legal implications that can and will follow are not pretty.