Need for to acquire one visa first

I want to stay in Delhi, India for three days before I go to Sri Lanka and after I visit Tibet. Do I have to get a visa? If I need one of it, does it already cover my next destination which is Sri Lanka, and may I just get a visa during my stay in Delhi?

There must be a separate visa for Sri Lanka and India. It is not possible to obtain them conjoined when you request it in one embassy or consulate. All visitors must acquire a visa before they arrive in India. However, if you are from Cambodia, Laos, Myanmar, Philippines, and Vietnam which are part of the ASEAN countries, you are allowed to acquire a visa upon your arrival in Delhi.
You can visit some helpful websites on the internet for you to get the details about getting a visa for visiting Sri Lanka.